draft-ietf-hip-mm-03.txt   draft-ietf-hip-mm-04.txt 
Network Working Group T. Henderson (editor) Network Working Group T. Henderson (editor)
Internet-Draft The Boeing Company Internet-Draft The Boeing Company
Expires: August 28, 2006 February 24, 2006 Expires: December 25, 2006 June 23, 2006
End-Host Mobility and Multihoming with the Host Identity Protocol End-Host Mobility and Multihoming with the Host Identity Protocol
draft-ietf-hip-mm-03 draft-ietf-hip-mm-04
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document defines mobility and multihoming extensions to the Host This document defines mobility and multihoming extensions to the Host
Identity Protocol (HIP). Specifically, this document defines a Identity Protocol (HIP). Specifically, this document defines a
general "LOCATOR" parameter for HIP messages that allows for a HIP general "LOCATOR" parameter for HIP messages that allows for a HIP
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the same LOCATOR parameter can also be used to support end-host the same LOCATOR parameter can also be used to support end-host
multihoming, detailed procedures are left for further study. multihoming, detailed procedures are left for further study.
Table of Contents Table of Contents
1. Introduction and Scope . . . . . . . . . . . . . . . . . . . . 4 1. Introduction and Scope . . . . . . . . . . . . . . . . . . . . 4
2. Terminology and Conventions . . . . . . . . . . . . . . . . . 6 2. Terminology and Conventions . . . . . . . . . . . . . . . . . 6
3. Protocol Model . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Protocol Model . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Operating Environment . . . . . . . . . . . . . . . . . . 7 3.1. Operating Environment . . . . . . . . . . . . . . . . . . 7
3.1.1. Locator . . . . . . . . . . . . . . . . . . . . . . . 9 3.1.1. Locator . . . . . . . . . . . . . . . . . . . . . . . 9
3.1.2. Mobility overview . . . . . . . . . . . . . . . . . . 10 3.1.2. Mobility overview . . . . . . . . . . . . . . . . . . 9
3.1.3. Multihoming overview . . . . . . . . . . . . . . . . . 10 3.1.3. Multihoming overview . . . . . . . . . . . . . . . . . 10
3.2. Protocol Overview . . . . . . . . . . . . . . . . . . . . 10 3.2. Protocol Overview . . . . . . . . . . . . . . . . . . . . 10
3.2.1. Mobility with single SA pair (no rekeying) . . . . . . 11 3.2.1. Mobility with single SA pair (no rekeying) . . . . . . 11
3.2.2. Host multihoming . . . . . . . . . . . . . . . . . . . 13 3.2.2. Mobility with single SA pair (mobile-initiated
3.2.3. Site multihoming . . . . . . . . . . . . . . . . . . . 15 rekey) . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.4. Dual host multihoming . . . . . . . . . . . . . . . . 15 3.2.3. Host multihoming . . . . . . . . . . . . . . . . . . . 13
3.2.5. Combined mobility and multihoming . . . . . . . . . . 16 3.2.4. Site multihoming . . . . . . . . . . . . . . . . . . . 14
3.2.6. Using LOCATORs across addressing realms . . . . . . . 16 3.2.5. Dual host multihoming . . . . . . . . . . . . . . . . 15
3.2.7. Network renumbering . . . . . . . . . . . . . . . . . 16 3.2.6. Combined mobility and multihoming . . . . . . . . . . 15
3.2.8. Initiating the protocol in R1 or I2 . . . . . . . . . 16 3.2.7. Using LOCATORs across addressing realms . . . . . . . 16
3.2.8. Network renumbering . . . . . . . . . . . . . . . . . 16
3.2.9. Initiating the protocol in R1 or I2 . . . . . . . . . 16
3.3. Other Considerations . . . . . . . . . . . . . . . . . . . 17 3.3. Other Considerations . . . . . . . . . . . . . . . . . . . 17
3.3.1. Address Verification . . . . . . . . . . . . . . . . . 17 3.3.1. Address Verification . . . . . . . . . . . . . . . . . 18
3.3.2. Credit-Based Authorization . . . . . . . . . . . . . . 18 3.3.2. Credit-Based Authorization . . . . . . . . . . . . . . 18
3.3.3. Preferred locator . . . . . . . . . . . . . . . . . . 19 3.3.3. Preferred locator . . . . . . . . . . . . . . . . . . 19
3.3.4. Interaction with Security Associations . . . . . . . . 20 3.3.4. Interaction with Security Associations . . . . . . . . 20
4. LOCATOR parameter format . . . . . . . . . . . . . . . . . . . 23 4. LOCATOR parameter format . . . . . . . . . . . . . . . . . . . 23
4.1. Traffic Type and Preferred Locator . . . . . . . . . . . . 24 4.1. Traffic Type and Preferred locator . . . . . . . . . . . . 24
4.2. Locator Type and Locator . . . . . . . . . . . . . . . . . 25 4.2. Locator Type and Locator . . . . . . . . . . . . . . . . . 25
4.3. UPDATE packet with included LOCATOR . . . . . . . . . . . 25 4.3. UPDATE packet with included LOCATOR . . . . . . . . . . . 25
5. Processing rules . . . . . . . . . . . . . . . . . . . . . . . 26 5. Processing rules . . . . . . . . . . . . . . . . . . . . . . . 26
5.1. Locator data structure and status . . . . . . . . . . . . 26 5.1. Locator data structure and status . . . . . . . . . . . . 26
5.2. Sending LOCATORs . . . . . . . . . . . . . . . . . . . . . 26 5.2. Sending LOCATORs . . . . . . . . . . . . . . . . . . . . . 27
5.3. Handling received LOCATORs . . . . . . . . . . . . . . . . 28 5.3. Handling received LOCATORs . . . . . . . . . . . . . . . . 29
5.4. Verifying address reachability . . . . . . . . . . . . . . 30 5.4. Verifying address reachability . . . . . . . . . . . . . . 30
5.5. Credit-Based Authorization . . . . . . . . . . . . . . . . 31 5.5. Changing the Preferred locator . . . . . . . . . . . . . . 31
5.5.1. Handling Payload Packets . . . . . . . . . . . . . . . 31 5.6. Credit-Based Authorization . . . . . . . . . . . . . . . . 32
5.5.2. Credit Aging . . . . . . . . . . . . . . . . . . . . . 33 5.6.1. Handling Payload Packets . . . . . . . . . . . . . . . 32
5.6. Changing the preferred locator . . . . . . . . . . . . . . 34 5.6.2. Credit Aging . . . . . . . . . . . . . . . . . . . . . 34
6. Security Considerations . . . . . . . . . . . . . . . . . . . 36 6. Security Considerations . . . . . . . . . . . . . . . . . . . 36
6.1. Impersonation attacks . . . . . . . . . . . . . . . . . . 36 6.1. Impersonation attacks . . . . . . . . . . . . . . . . . . 36
6.2. Denial of Service attacks . . . . . . . . . . . . . . . . 37 6.2. Denial of Service attacks . . . . . . . . . . . . . . . . 37
6.2.1. Flooding Attacks . . . . . . . . . . . . . . . . . . . 37 6.2.1. Flooding Attacks . . . . . . . . . . . . . . . . . . . 37
6.2.2. Memory/Computational exhaustion DoS attacks . . . . . 38 6.2.2. Memory/Computational exhaustion DoS attacks . . . . . 38
6.3. Mixed deployment environment . . . . . . . . . . . . . . . 38 6.3. Mixed deployment environment . . . . . . . . . . . . . . . 38
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40
8. Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 8. Authors and Acknowledgments . . . . . . . . . . . . . . . . . 41
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 42 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 42
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 43 9.1. Normative references . . . . . . . . . . . . . . . . . . . 42
10.1. Normative references . . . . . . . . . . . . . . . . . . . 43 9.2. Informative references . . . . . . . . . . . . . . . . . . 42
10.2. Informative references . . . . . . . . . . . . . . . . . . 43 Appendix A. Changes from previous versions . . . . . . . . . . . 43
Appendix A. Changes from previous versions . . . . . . . . . . . 44 A.1. From nikander-hip-mm-00 to nikander-hip-mm-01 . . . . . . 43
A.1. From nikander-hip-mm-00 to nikander-hip-mm-01 . . . . . . 44 A.2. From nikander-hip-mm-01 to nikander-hip-mm-02 . . . . . . 43
A.2. From nikander-hip-mm-01 to nikander-hip-mm-02 . . . . . . 44 A.3. From -02 to draft-ietf-hip-mm-00 . . . . . . . . . . . . . 43
A.3. From -02 to draft-ietf-hip-mm-00 . . . . . . . . . . . . . 44 A.4. From draft-ietf-hip-mm-00 to -01 . . . . . . . . . . . . . 44
A.4. From draft-ietf-hip-mm-00 to -01 . . . . . . . . . . . . . 45 A.5. From draft-ietf-hip-mm-01 to -02 . . . . . . . . . . . . . 44
A.5. From draft-ietf-hip-mm-01 to -02 . . . . . . . . . . . . . 45 A.6. From draft-ietf-hip-mm-02 to -03 . . . . . . . . . . . . . 44
A.6. From draft-ietf-hip-mm-02 to -03 . . . . . . . . . . . . . 45 A.7. From draft-ietf-hip-mm-03 to -04 . . . . . . . . . . . . . 45
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 47 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 46
Intellectual Property and Copyright Statements . . . . . . . . . . 48 Intellectual Property and Copyright Statements . . . . . . . . . . 47
1. Introduction and Scope 1. Introduction and Scope
The Host Identity Protocol [1] (HIP) supports an architecture that The Host Identity Protocol [1] (HIP) supports an architecture that
decouples the transport layer (TCP, UDP, etc.) from the decouples the transport layer (TCP, UDP, etc.) from the
internetworking layer (IPv4 and IPv6) by using public/private key internetworking layer (IPv4 and IPv6) by using public/private key
pairs, instead of IP addresses, as host identities. When a host uses pairs, instead of IP addresses, as host identities. When a host uses
HIP, the overlying protocol sublayers (e.g., transport layer sockets HIP, the overlying protocol sublayers (e.g., transport layer sockets
and ESP Security Associations) are instead bound to representations and ESP Security Associations) are instead bound to representations
of these host identities, and the IP addresses are only used for of these host identities, and the IP addresses are only used for
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change in preferred IP address used to reach a host. In change in preferred IP address used to reach a host. In
particular, message flows to enable successful host mobility, particular, message flows to enable successful host mobility,
including address verification methods, are defined herein. including address verification methods, are defined herein.
However, while the same LOCATOR parameter is intended to support However, while the same LOCATOR parameter is intended to support
host multihoming (parallel support of a number of addresses), and host multihoming (parallel support of a number of addresses), and
experimentation is encouraged, detailed elements of procedure for experimentation is encouraged, detailed elements of procedure for
host multihoming are left for further study. host multihoming are left for further study.
While HIP can potentially be used with transports other than the ESP While HIP can potentially be used with transports other than the ESP
transport format [5], this document largely assumes the use of ESP transport format [6], this document largely assumes the use of ESP
and leaves other transport for further study. and leaves other transport for further study.
There are a number of situations where the simple end-to-end There are a number of situations where the simple end-to-end
readdressing functionality is not sufficient. These include the readdressing functionality is not sufficient. These include the
initial reachability of a mobile host, location privacy, simultaneous initial reachability of a mobile host, location privacy, simultaneous
mobility of both hosts, and some modes of NAT traversal. In these mobility of both hosts, and some modes of NAT traversal. In these
situations there is a need for some helper functionality in the situations there is a need for some helper functionality in the
network, such as a HIP Rendezvous server [3]. Such functionality is network, such as a HIP Rendezvous server [3]. Such functionality is
out of scope of this document. We also do not consider localized out of scope of this document. We also do not consider localized
mobility management extensions; this document is concerned with end- mobility management extensions (i.e., mobility management techniques
to-end mobility. Finally, making underlying IP mobility transparent that do not involve directly signaling the correspondent node); this
to the transport layer has implications on the proper response of document is concerned with end-to-end mobility. Finally, making
transport congestion control, path MTU selection, and QoS. underlying IP mobility transparent to the transport layer has
Transport-layer mobility triggers, and the proper transport response implications on the proper response of transport congestion control,
to a HIP mobility or multihoming address change, are outside the path MTU selection, and QoS. Transport-layer mobility triggers, and
scope of this document. the proper transport response to a HIP mobility or multihoming
address change, are outside the scope of this document.
2. Terminology and Conventions 2. Terminology and Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [6]. document are to be interpreted as described in RFC2119 [7].
LOCATOR. The name of a HIP parameter containing zero or more Locator
fields. This parameter's name is distinguished from the Locator
fields embedded within it by the use of all capital letters.
Locator. A name that controls how the packet is routed through the Locator. A name that controls how the packet is routed through the
network and demultiplexed by the end host. It may include a network and demultiplexed by the end host. It may include a
concatenation of traditional network addresses such as an IPv6 concatenation of traditional network addresses such as an IPv6
address and end-to-end identifiers such as an ESP SPI. It may address and end-to-end identifiers such as an ESP SPI. It may
also include transport port numbers or IPv6 Flow Labels as also include transport port numbers or IPv6 Flow Labels as
demultiplexing context, or it may simply be a network address. demultiplexing context, or it may simply be a network address.
Address. A name that denotes a point-of-attachment to the network. Address. A name that denotes a point-of-attachment to the network.
The two most common examples are an IPv4 address and an IPv6 The two most common examples are an IPv4 address and an IPv6
address. The set of possible addresses is a subset of the set of address. The set of possible addresses is a subset of the set of
possible locators. possible locators.
Preferred locator. A locator on which a host prefers to receive data. Preferred locator. A locator on which a host prefers to receive data.
With respect to a given peer, a host always has one active With respect to a given peer, a host always has one active
preferred locator, unless there are no active locators. By Preferred locator, unless there are no active locators. By
default, the locators used in the HIP base exchange are the default, the locators used in the HIP base exchange are the
preferred locators. Preferred locators.
Credit Based Authorization. A host must verify a mobile or multi- Credit Based Authorization. A host must verify a mobile or multi-
homed peer's reachability at a new locator. Credit-Based homed peer's reachability at a new locator. Credit-Based
Authorization authorizes the peer to receive a certain amount of Authorization authorizes the peer to receive a certain amount of
data at the new locator before the result of such verification is data at the new locator before the result of such verification is
known. known.
3. Protocol Model 3. Protocol Model
This section is an overview; more detailed specification follows this
section.
3.1. Operating Environment 3.1. Operating Environment
The Host Identity Protocol (HIP) [2] is a key establishment and The Host Identity Protocol (HIP) [2] is a key establishment and
parameter negotiation protocol. Its primary applications are for parameter negotiation protocol. Its primary applications are for
authenticating host messages based on host identities, and authenticating host messages based on host identities, and
establishing security associations (SAs) for ESP transport format [5] establishing security associations (SAs) for ESP transport format [6]
and possibly other protocols in the future. and possibly other protocols in the future.
+--------------------+ +--------------------+ +--------------------+ +--------------------+
| | | | | | | |
| +------------+ | | +------------+ | | +------------+ | | +------------+ |
| | Key | | HIP | | Key | | | | Key | | HIP | | Key | |
| | Management | <-+-----------------------+-> | Management | | | | Management | <-+-----------------------+-> | Management | |
| | Process | | | | Process | | | | Process | | | | Process | |
| +------------+ | | +------------+ | | +------------+ | | +------------+ |
| ^ | | ^ | | ^ | | ^ |
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| +------------+ | | +------------+ | | +------------+ | | +------------+ |
| | | | | | | |
| | | | | | | |
| Initiator | | Responder | | Initiator | | Responder |
+--------------------+ +--------------------+ +--------------------+ +--------------------+
Figure 1: HIP deployment model Figure 1: HIP deployment model
The general deployment model for HIP is shown above, assuming The general deployment model for HIP is shown above, assuming
operation in an end-to-end fashion. This document specifies operation in an end-to-end fashion. This document specifies
extensions to the HIP protocol to enable end-host mobility and extensions to the HIP protocol to enable end-host mobility and basic
multihoming. In summary, these extensions to the HIP protocol can multihoming. In summary, these extensions to the HIP base protocol
carry new addressing information to the peer and can enable direct enable the signaling of new addressing information to the peer in HIP
authentication of the message via a signature or keyed hash message messages. The messages are authenticated via a signature or keyed
authentication code (HMAC) based on its host identity. This document hash message authentication code (HMAC) based on its host identity.
specifies the format of this new addressing (LOCATOR) parameter, the This document specifies the format of this new addressing (LOCATOR)
procedures for sending and processing this parameter to enable basic parameter, the procedures for sending and processing this parameter
host mobility, and procedures for a concurrent address verification to enable basic host mobility, and procedures for a concurrent
mechanism. address verification mechanism.
--------- ---------
| TCP | (sockets bound to HITs) | TCP | (sockets bound to HITs)
--------- ---------
| |
--------- ---------
----> | ESP | {HIT_s, HIT_d} <-> SPI ----> | ESP | {HIT_s, HIT_d} <-> SPI
| --------- | ---------
| | | |
---- --------- ---- ---------
| MH |-> | HIP | {HIT_s, HIT_d, SPI} <-> {IP_s, IP_d, SPI} | MH |-> | HIP | {HIT_s, HIT_d, SPI} <-> {IP_s, IP_d, SPI}
---- --------- ---- ---------
| |
--------- ---------
| IP | | IP |
--------- ---------
Figure 2: Architecture for HIP mobility and multihoming Figure 2: Architecture for HIP mobility and multihoming (MH)
Figure 2 depicts a layered architectural view of a HIP-enabled stack Figure 2 depicts a layered architectural view of a HIP-enabled stack
using ESP transport format. In HIP, upper-layer protocols (including using ESP transport format. In HIP, upper-layer protocols (including
TCP and ESP in this figure) are bound to HITs and not IP addresses. TCP and ESP in this figure) are bound to HITs and not IP addresses.
The HIP sublayer is responsible for maintaining the binding between The HIP sublayer is responsible for maintaining the binding between
HITs and IP addresses. The SPI (or other context tag if ESP is not HITs and IP addresses. The SPI is used to associate an incoming
used with HIP), and not necessarily the IP addresses, is used to packet with the right HITs. The block labeled "MH" is introduced
associate an incoming packet with the right HITs. The block labeled below.
"MH" is introduced below.
Consider first the case in which there is no mobility or multihoming, Consider first the case in which there is no mobility or multihoming,
as specified in the base protocol specification [2]. The HIP base as specified in the base protocol specification [2]. The HIP base
exchange establishes the HITs in use between the hosts, the SPIs to exchange establishes the HITs in use between the hosts, the SPIs to
use for ESP, and the IP addresses (used in the HIP signaling use for ESP, and the IP addresses (used in both the HIP signaling
packets). Note that there can only be one such binding in the packets and ESP data packets). Note that there can only be one such
outbound direction for any given packet, and the only selectors for set of bindings in the outbound direction for any given packet, and
the binding at the HIP layer are the fields exposed by ESP (the SPI the only fields used for the binding at the HIP layer are the fields
and HITs). For the inbound direction, the SPI is all that is exposed by ESP (the SPI and HITs). For the inbound direction, the
required to find the right host context. ESP rekeying events change SPI is all that is required to find the right host context. ESP
the mapping between the HIT pair and SPI, but do not change the IP rekeying events change the mapping between the HIT pair and SPI, but
addresses. do not change the IP addresses.
Consider next a mobility event, in which a host is still single-homed Consider next a mobility event, in which a host is still single-homed
but moves to another IP address. Two things must occur in this case. but moves to another IP address. Two things must occur in this case.
First, the peer must be notified of the address change using a HIP First, the peer must be notified of the address change using a HIP
UPDATE message. Second, each host must change its local bindings at UPDATE message. Second, each host must change its local bindings at
the HIP sublayer (new IP addresses). It may be that both the SPIs the HIP sublayer (new IP addresses). It may be that both the SPIs
and IP addresses are changed simultaneously in a single UPDATE; the and IP addresses are changed simultaneously in a single UPDATE; the
protocol described herein supports this. This document specifies the protocol described herein supports this. However, simultaneous
messaging and elements of procedure for such a mobility event. movement of both hosts, notification of transport layer protocols of
However, simultaneous movement of both hosts, notification of the path change, and procedures for possibly traversing middleboxes
transport layer protocols of the path change, and procedures for are not covered by this document.
possibly traversing middleboxes are not covered by this document.
Finally, consider the case when a host is multihomed (has more than Finally, consider the case when a host is multihomed (has more than
one globally routable address) and wants to make these multiple one globally routable address) and makes these multiple addresses
addresses available for use by the upper layer protocols, for fault available for use by the upper layer protocols, for fault tolerance.
tolerance. Examples include the use of (possibly multiple) IPv4 and Examples include the use of (possibly multiple) IPv4 and IPv6
IPv6 addresses on the same interface, or the use of multiple addresses on the same interface, or the use of multiple interfaces
interfaces attached to different service providers. Such host attached to different service providers. Such host multihoming
multihoming generally necessitates that a separate ESP SA is generally necessitates that a separate ESP SA is maintained for each
maintained for each interface in order to prevent packets that arrive interface in order to prevent packets that arrive over different
over different paths from falling outside of the ESP replay paths from falling outside of the ESP replay protection window.
protection window. Multihoming thus makes possible that the bindings Multihoming thus makes possible that the bindings shown on the right
shown on the right side of Figure 2 are one to many (in the outbound side of Figure 2 are one to many (in the outbound direction, one HIT
direction, one HIT pair to multiple SPIs, and possibly then to pair to multiple SPIs, and possibly then to multiple IP addresses).
multiple IP addresses). However, only one SPI and address can be However, only one SPI and address pair can be used for any given
used for any given packet, so the job of the "MH" block depicted packet, so the job of the "MH" block depicted above is to dynamically
above is to dynamically manipulate these bindings. Beyond locally manipulate these bindings. Beyond locally managing such multiple
managing such multiple bindings, the peer-to-peer HIP signaling bindings, the peer-to-peer HIP signaling protocol needs to be
protocol needs to be flexible enough to define the desired mappings flexible enough to define the desired mappings between HITs, SPIs,
between HITs, SPIs, and addresses, and needs to ensure that UPDATE and addresses, and needs to ensure that UPDATE messages are sent
messages are sent along the right network paths so that any HIP-aware along the right network paths so that any HIP-aware middleboxes can
middleboxes can observe the SPIs. This document does not specify the observe the SPIs. This document does not specify the "MH" block, nor
"MH" block, nor does it specify detailed elements of procedure for does it specify detailed elements of procedure for how to handle
how to handle various multihoming (perhaps combined with mobility) various multihoming (perhaps combined with mobility) scenarios. The
scenarios. However, this document does describe a basic multihoming "MH" block may apply to more general problems outside of HIP.
case (one host adds one address to its initial address and notifies However, this document does describe a basic multihoming case (one
the peer) and leave more complicated scenarios for experimentation host adds one address to its initial address and notifies the peer)
and future documents. and leave more complicated scenarios for experimentation and future
documents.
3.1.1. Locator 3.1.1. Locator
This document defines a generalization of an address called a This document defines a generalization of an address called a
"locator". A locator specifies a point-of-attachment to the network "locator". A locator specifies a point-of-attachment to the network
but may also include additional end-to-end tunneling or per-host but may also include additional end-to-end tunneling or per-host
demultiplexing context that affects how packets are handled below the demultiplexing context that affects how packets are handled below the
logical HIP sublayer of the stack. This generalization is useful logical HIP sublayer of the stack. This generalization is useful
because IP addresses alone may not be sufficient to describe how because IP addresses alone may not be sufficient to describe how
packets should be handled below HIP. For example, in a host packets should be handled below HIP. For example, in a host
multihoming context, certain IP addresses may need to be associated multihoming context, certain IP addresses may need to be associated
with certain ESP SPIs, to avoid violation of the ESP anti-replay with certain ESP SPIs, to avoid violation of the ESP anti-replay
window [4]. Addresses may also be affiliated with transport ports in window [4]. Addresses may also be affiliated with transport ports in
certain tunneling scenarios. Or locators may merely be traditional certain tunneling scenarios. Locators may simply be traditional
network addresses. In Section 4, a generalized HIP LOCATOR parameter network addresses. The format of the locators is defined in
is defined that can contain one or more locators (addresses). Section 4.
3.1.2. Mobility overview 3.1.2. Mobility overview
When a host moves to another address, it notifies its peer of the new When a host moves to another address, it notifies its peer of the new
address by sending a HIP UPDATE packet containing a LOCATOR address by sending a HIP UPDATE packet containing a LOCATOR
parameter. This UPDATE packet is acknowledged by the peer, and is parameter. This UPDATE packet is acknowledged by the peer, and is
protected by retransmission. The peer can authenticate the contents protected by retransmission. The peer can authenticate the contents
of the UPDATE packet based on the signature and keyed hash of the of the UPDATE packet based on the signature and keyed hash of the
packet. packet.
When using ESP Transport Format [5], the host may at the same time When using ESP Transport Format [6], the host may at the same time
decide to rekey its security association and possibly generate a new decide to rekey its security association and possibly generate a new
Diffie-Hellman key; all of these actions are triggered by including Diffie-Hellman key; all of these actions are triggered by including
additional parameters in the UPDATE packet, as defined in the base additional parameters in the UPDATE packet, as defined in the base
protocol specification [2] and ESP extension [5]. protocol specification [2] and ESP extension [6].
When using ESP (and possibly other transport modes in the future), When using ESP (and possibly other transport modes in the future),
the host is able to receive packets that are protected using a HIP the host is able to receive packets that are protected using a HIP
created ESP SA from any address. Thus, a host can change its IP created ESP SA from any address. Thus, a host can change its IP
address and continue to send packets to its peers without necessarily address and continue to send packets to its peers without necessarily
rekeying. However, the peers are not able to reply before they can rekeying. However, the peers are not able to send packets to these
reliably and securely update the set of addresses that they associate new addresses before they can reliably and securely update the set of
with the sending host. Furthermore, mobility may change the path addresses that they associate with the sending host. Furthermore,
characteristics in such a manner that reordering occurs and packets mobility may change the path characteristics in such a manner that
fall outside the ESP anti-replay window for the SA, thereby requiring reordering occurs and packets fall outside the ESP anti-replay window
rekeying. for the SA, thereby requiring rekeying.
3.1.3. Multihoming overview 3.1.3. Multihoming overview
A related operational configuration is host multihoming, in which a A related operational configuration is host multihoming, in which a
host has multiple locators simultaneously rather than sequentially as host has multiple locators simultaneously rather than sequentially as
in the case of mobility. By using the LOCATOR parameter defined in the case of mobility. By using the LOCATOR parameter defined
herein, a host can inform its peers of additional (multiple) locators herein, a host can inform its peers of additional (multiple) locators
at which it can be reached, and can declare a particular locator as a at which it can be reached, and can declare a particular locator as a
"preferred" locator. Although this document defines a mechanism for "preferred" locator. Although this document defines a basic
multihoming, it does not define detailed policies and procedures such mechanism for multihoming, it does not define detailed policies and
as which locators to choose when more than one pair is available, the procedures such as which locators to choose when more than one pair
operation of simultaneous mobility and multihoming, and the is available, the operation of simultaneous mobility and multihoming,
implications of multihoming on transport protocols and ESP anti- source address selection policies (beyond those specified in [5]),
replay windows. Additional definition of HIP-based multihoming is and the implications of multihoming on transport protocols and ESP
expected to be part of future documents. anti-replay windows. Additional definition of HIP-based multihoming
is expected to be part of future documents.
3.2. Protocol Overview 3.2. Protocol Overview
In this section we briefly introduce a number of usage scenarios for In this section we briefly introduce a number of usage scenarios for
HIP mobility and multihoming. These scenarios assume that HIP is HIP mobility and multihoming. These scenarios assume that HIP is
being used with the ESP transform [5], although other scenarios may being used with the ESP transform [6], although other scenarios may
be defined in the future. To understand these usage scenarios, the be defined in the future. To understand these usage scenarios, the
reader should be at least minimally familiar with the HIP protocol reader should be at least minimally familiar with the HIP protocol
specification [2]. However, for the (relatively) uninitiated reader specification [2]. However, for the (relatively) uninitiated reader
it is most important to keep in mind that in HIP the actual payload it is most important to keep in mind that in HIP the actual payload
traffic is protected with ESP, and that the ESP SPI acts as an index traffic is protected with ESP, and that the ESP SPI acts as an index
to the right host-to-host context. to the right host-to-host context. More specification detail on is
later found in Section 4 and Section 5.
Each of the scenarios below assumes that the HIP base exchange has The scenarios below assume that the two hosts have completed a single
completed, and the hosts each have a single outbound SA to the peer HIP base exchange with each other. Both of the hosts therefore have
host. Associated with this outbound SA is a single destination one incoming and one outgoing SA. Further, each SA uses the same
address of the peer host-- the source address used by the peer during pair of IP addresses; the ones used in the base exchange.
the base exchange.
The readdressing protocol is an asymmetric protocol where a mobile or The readdressing protocol is an asymmetric protocol where a mobile or
multihomed host informs a peer host about changes of IP addresses on multihomed host informs a peer host about changes of IP addresses on
affected SPIs. The readdressing exchange is designed to be affected SPIs. The readdressing exchange is designed to be
piggybacked on existing HIP exchanges. The main packets on which the piggybacked on existing HIP exchanges. The majority of the packets
LOCATOR parameters are expected to be carried are UPDATE packets. on which the LOCATOR parameters are expected to be carried are UPDATE
However, some implementations may want to experiment with sending packets. However, some implementations may want to experiment with
LOCATOR parameters also on other packets, such as R1, I2, and NOTIFY. sending LOCATOR parameters also on other packets, such as R1, I2, and
NOTIFY.
Hosts that use link-local addresses as source addresses in their HIP Hosts that use link-local addresses as source addresses in their HIP
handshakes may not be reachable by a mobile peer. Such hosts SHOULD handshakes may not be reachable by a mobile peer. Such hosts SHOULD
provide a globally routable address either in the initial handshake provide a globally routable address either in the initial handshake
or via the LOCATOR parameter. or via the LOCATOR parameter.
3.2.1. Mobility with single SA pair (no rekeying) 3.2.1. Mobility with single SA pair (no rekeying)
A mobile host must sometimes change an IP address bound to an A mobile host must sometimes change an IP address bound to an
interface. The change of an IP address might be needed due to a interface. The change of an IP address might be needed due to a
skipping to change at page 12, line 4 skipping to change at page 11, line 50
Mobile Host Peer Host Mobile Host Peer Host
UPDATE(ESP_INFO, LOCATOR, SEQ) UPDATE(ESP_INFO, LOCATOR, SEQ)
-----------------------------------> ----------------------------------->
UPDATE(ESP_INFO, SEQ, ACK, ECHO_REQUEST) UPDATE(ESP_INFO, SEQ, ACK, ECHO_REQUEST)
<----------------------------------- <-----------------------------------
UPDATE(ACK, ECHO_RESPONSE) UPDATE(ACK, ECHO_RESPONSE)
-----------------------------------> ----------------------------------->
Figure 3: Readdress without rekeying, but with address check Figure 3: Readdress without rekeying, but with address check
The steps of the packet processing are as follows:
1. The mobile host is disconnected from the peer host for a brief 1. The mobile host is disconnected from the peer host for a brief
period of time while it switches from one IP address to another. period of time while it switches from one IP address to another.
Upon obtaining a new IP address, the mobile host sends a LOCATOR Upon obtaining a new IP address, the mobile host sends a LOCATOR
parameter to the peer host in an UPDATE message. The UPDATE parameter to the peer host in an UPDATE message. The UPDATE
message also contains an ESP_INFO parameter with the "Old SPI" message also contains an ESP_INFO parameter containing the values
and "New SPI" parameters both set to the value of the pre- of the old and new SPIs for a security association. In this
existing incoming SPI; this ESP_INFO does not trigger a rekeying case, the "Old SPI" and "New SPI" parameters both are set to the
event but is instead included for possible parameter-inspecting value of the pre-existing incoming SPI; this ESP_INFO does not
middleboxes on the path. The LOCATOR parameter contains the new trigger a rekeying event but is instead included for possible
IP address (Locator Type of "1", defined below) and a locator parameter-inspecting middleboxes on the path. The LOCATOR
lifetime. The mobile host waits for this UPDATE to be parameter contains the new IP address (Locator Type of "1",
acknowledged, and retransmits if necessary, as specified in the defined below) and a locator lifetime. The mobile host waits for
base specification [2]. this UPDATE to be acknowledged, and retransmits if necessary, as
specified in the base specification [2].
2. The peer host receives the UPDATE, validates it, and updates any 2. The peer host receives the UPDATE, validates it, and updates any
local bindings between the HIP association and the mobile host's local bindings between the HIP association and the mobile host's
destination address. The peer host MUST perform an address destination address. The peer host MUST perform an address
verification by placing a nonce in the ECHO_REQUEST parameter of verification by placing a nonce in the ECHO_REQUEST parameter of
hte UPDATE message sent back to the mobile host. It also the UPDATE message sent back to the mobile host. It also
includes an ESP_INFO parameter with the "Old SPI" and "New SPI" includes an ESP_INFO parameter with the "Old SPI" and "New SPI"
parameters both set to the value of the pre-existing incoming parameters both set to the value of the pre-existing incoming
SPI, and sends this UPDATE (with piggybacked acknowledgment) to SPI, and sends this UPDATE (with piggybacked acknowledgment) to
the mobile host at its new address. The peer MAY use the new the mobile host at its new address. The peer MAY use the new
address immediately, but it MUST limit the amount of data it address immediately, but it MUST limit the amount of data it
sends to the address until address verification completes. sends to the address until address verification completes.
3. The mobile host completes the readdress by processing the UPDATE 3. The mobile host completes the readdress by processing the UPDATE
ACK and echoing the nonce in an ECHO_RESPONSE. Once the peer ACK and echoing the nonce in an ECHO_RESPONSE. Once the peer
host receives this ECHO_RESPONSE, it considers the new address to host receives this ECHO_RESPONSE, it considers the new address to
be verified and can put it into full use. be verified and can put it into full use.
While the peer host is verifying the new address, the new address is While the peer host is verifying the new address, the new address is
marked as UNVERIFIED in the interim, and the old address is marked as UNVERIFIED in the interim, and the old address is
DEPRECATED. Once the peer host has received a correct reply to its DEPRECATED. Once the peer host has received a correct reply to its
UPDATE challenge, it marks the new address as ACTIVE and removes the UPDATE challenge, it marks the new address as ACTIVE and removes the
old address. old address.
3.2.1.1. Mobility with single SA pair (mobile-initiated rekey) 3.2.2. Mobility with single SA pair (mobile-initiated rekey)
The mobile host may decide to rekey the SAs at the same time that it The mobile host may decide to rekey the SAs at the same time that it
is notifying the peer of the new address. In this case, the above is notifying the peer of the new address. In this case, the above
procedure described in Figure 3 is slightly modified. The UPDATE procedure described in Figure 3 is slightly modified. The UPDATE
message sent from the mobile host includes an ESP_INFO with the "Old message sent from the mobile host includes an ESP_INFO with the "Old
SPI" set to the previous SPI, the "New SPI" set to the desired new SPI" set to the previous SPI, the "New SPI" set to the desired new
SPI value for the incoming SA, and the Keymat Index desired. SPI value for the incoming SA, and the Keymat Index desired.
Optionally, the host may include a DIFFIE_HELLMAN parameter for a new Optionally, the host may include a DIFFIE_HELLMAN parameter for a new
Diffie-Hellman key. The peer completes the request for rekey as is Diffie-Hellman key. The peer completes the request for rekey as is
normally done for HIP rekeying, except that the new address is kept normally done for HIP rekeying, except that the new address is kept
skipping to change at page 13, line 18 skipping to change at page 13, line 19
UPDATE(ESP_INFO, LOCATOR, SEQ, [DIFFIE_HELLMAN]) UPDATE(ESP_INFO, LOCATOR, SEQ, [DIFFIE_HELLMAN])
-----------------------------------> ----------------------------------->
UPDATE(ESP_INFO, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST) UPDATE(ESP_INFO, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST)
<----------------------------------- <-----------------------------------
UPDATE(ACK, ECHO_RESPONSE) UPDATE(ACK, ECHO_RESPONSE)
-----------------------------------> ----------------------------------->
Figure 4: Readdress with mobile-initiated rekey Figure 4: Readdress with mobile-initiated rekey
3.2.1.2. Mobility with single SA pair (peer-initiated rekey) 3.2.3. Host multihoming
A second variation of this basic mobility scenario covers the case in
which the mobile host does not attempt to rekey the existing SAs, but
the peer host decides to do so. This typically results in a four
packet exchange, as shown in Figure 5. The initial UPDATE packet
from the mobile host is the same as in the scenario for which there
is no rekey (Figure 3). The peer may decide to rekey, however, in
which case the subsequent three packets follow the normal rekeying
procedure described in the ESP specification [5], with the addition
of the ECHO_REQUEST and ECHO_RESPONSE nonce for verification of the
new address.
Mobile Host Peer Host
UPDATE(ESP_INFO, LOCATOR, SEQ)
----------------------------------->
UPDATE(ESP_INFO, SEQ, ACK, [DIFFIE_HELLMAN], ECHO_REQUEST)
<-----------------------------------
UPDATE(ESP_INFO, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_RESPONSE)
----------------------------------->
UPDATE(ACK)
<-----------------------------------
Figure 5: Readdress with peer-initiated rekey
3.2.2. Host multihoming
A (mobile or stationary) host may sometimes have more than one A (mobile or stationary) host may sometimes have more than one
interface or global address. The host may notify the peer host of interface or global address. The host may notify the peer host of
the additional interface or address by using the LOCATOR parameter. the additional interface or address by using the LOCATOR parameter.
To avoid problems with the ESP anti-replay window, a host SHOULD use To avoid problems with the ESP anti-replay window, a host SHOULD use
a different SA for each interface or address used to receive packets a different SA for each interface or address used to receive packets
from the peer host. from the peer host.
When more than one locator is provided to the peer host, the host When more than one locator is provided to the peer host, the host
SHOULD indicate which locator is preferred. By default, the SHOULD indicate which locator is preferred. By default, the
skipping to change at page 14, line 24 skipping to change at page 13, line 47
created pairwise between hosts. When an ESP_INFO arrives to rekey a created pairwise between hosts. When an ESP_INFO arrives to rekey a
particular outbound SA, the corresponding inbound SA should be also particular outbound SA, the corresponding inbound SA should be also
rekeyed at that time. Although asymmetric SA configurations might be rekeyed at that time. Although asymmetric SA configurations might be
experimented with, their usage may constrain interoperability at this experimented with, their usage may constrain interoperability at this
time. However, it is recommended that implementations attempt to time. However, it is recommended that implementations attempt to
support peers that prefer to use non-paired SAs. It is expected that support peers that prefer to use non-paired SAs. It is expected that
this section and behavior will be modified in future revisions of this section and behavior will be modified in future revisions of
this protocol, once the issue and its implications are better this protocol, once the issue and its implications are better
understood. understood.
Consider the case between two single-homed hosts, in which one of the Consider the case between two hosts, one single-homed and one
host notifies the peer of an additional address. It is RECOMMENDED multihomed. The multihomed host may decide to inform the single-
that the host set up a new SA pair for use on this new address. To homed host about its other address. It is RECOMMENDED that the
multihomed host set up a new SA pair for use on this new address. To
do this, the multihomed host sends a LOCATOR with an ESP_INFO, do this, the multihomed host sends a LOCATOR with an ESP_INFO,
indicating the request for a new SA by setting the "Old SPI" value to indicating the request for a new SA by setting the "Old SPI" value to
zero, and the "New SPI" value to the newly created incoming SPI. A zero, and the "New SPI" value to the newly created incoming SPI. A
Locator Type of "1" is used to associate the new address with the new Locator Type of "1" is used to associate the new address with the new
SPI. The LOCATOR parameter also contains a second Type 1 locator: SPI. The LOCATOR parameter also contains a second Type 1 locator:
that of the original address and SPI. To simplify parameter that of the original address and SPI. To simplify parameter
processing and avoid explicit protocol extensions to remove locators, processing and avoid explicit protocol extensions to remove locators,
each LOCATOR parameter must list all locators in use on a connection each LOCATOR parameter MUST list all locators in use on a connection
(a complete listing of inbound locators and SPIs for the host). The (a complete listing of inbound locators and SPIs for the host). The
multihomed host transitions to state REKEYING, waiting for a ESP_INFO multihomed host waits for a ESP_INFO (new outbound SA) from the peer
(new outbound SA) from the peer and an ACK of its own UPDATE. As in and an ACK of its own UPDATE. As in the mobility case, the peer host
the mobility case, the peer host must perform an address verification must perform an address verification before actively using the new
before putting the new address into active use. Figure 6 illustrates address. Figure 5 illustrates this scenario.
the basic packet exchange.
Multi-homed Host Peer Host Multi-homed Host Peer Host
UPDATE(ESP_INFO, LOCATOR, SEQ, [DIFFIE_HELLMAN]) UPDATE(ESP_INFO, LOCATOR, SEQ, [DIFFIE_HELLMAN])
-----------------------------------> ----------------------------------->
UPDATE(ESP_INFO, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST) UPDATE(ESP_INFO, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST)
<----------------------------------- <-----------------------------------
UPDATE(ACK, ECHO_RESPONSE) UPDATE(ACK, ECHO_RESPONSE)
-----------------------------------> ----------------------------------->
Figure 6: Basic multihoming scenario Figure 5: Basic multihoming scenario
When processing inbound LOCATORs that establish new security
associations on an interface with multiple addresses, a host uses the
destination address of the UPDATE containing LOCATOR as the local
address to which the LOCATOR plus ESP_INFO is targeted. Hosts may
send UPDATEs with the same IP address in the LOCATOR to different
peer addresses-- this has the effect of creating multiple inbound SAs
implicitly affiliated with different peer source addresses.
3.2.3. Site multihoming In multihoming scenarios, it is important that hosts receiving
UPDATEs associate them correctly with the destination address used in
the packet carrying the UPDATE. When processing inbound LOCATORs
that establish new security associations on an interface with
multiple addresses, a host uses the destination address of the UPDATE
containing LOCATOR as the local address to which the LOCATOR plus
ESP_INFO is targeted. This is because hosts may send UPDATEs with
the same (locator) IP address to different peer addresses-- this has
the effect of creating multiple inbound SAs implicitly affiliated
with different peer source addresses.
3.2.4. Site multihoming
A host may have an interface that has multiple globally reachable IP A host may have an interface that has multiple globally reachable IP
addresses. Such a situation may be a result of the site having addresses. Such a situation may be a result of the site having
multiple upper Internet Service Providers, or just because the site multiple upper Internet Service Providers, or just because the site
provides all hosts with both IPv4 and IPv6 addresses. It is provides all hosts with both IPv4 and IPv6 addresses. It is
desirable that the host can stay reachable with all or any subset of desirable that the host can stay reachable with all or any subset of
the currently available globally routable addresses, independent on the currently available globally routable addresses, independent on
how they are provided. how they are provided.
This case is handled the same as if there were different IP This case is handled the same as if there were different IP
addresses, described above in Section 3.2.2. Note that a single addresses, described above in Section 3.2.3. Note that a single
interface may experience site multihoming while the host itself may interface may experience site multihoming while the host itself may
have multiple interfaces. have multiple interfaces.
Note that a host may be multi-homed and mobile simultaneously, and Note that a host may be multi-homed and mobile simultaneously, and
that a multi-homed host may want to protect the location of some of that a multi-homed host may want to protect the location of some of
its interfaces while revealing the real IP address of some others. its interfaces while revealing the real IP address of some others.
This document does not presently specify additional site multihoming This document does not presently specify additional site multihoming
extensions to HIP; further alignment with the IETF shim6 working extensions to HIP; further alignment with the IETF shim6 working
group may be considered in the future. group may be considered in the future.
3.2.4. Dual host multihoming 3.2.5. Dual host multihoming
Consider the case in which both hosts would like to add an additional Consider the case in which both hosts would like to add an additional
address after the base exchange completes. In Figure 7, consider address after the base exchange completes. In Figure 6, consider
that host1 wants to add address addr1b. It would send an UPDATE with that host1, which used address addr1a in the base exchange to set up
LOCATOR to host2 located at addr2a, and a new set of SPIs would be SPI1a and SPI2a, wants to add address addr1b. It would send an
added between hosts 1 and 2 (call them SPI1b and SPI2b). Next, UPDATE with LOCATOR (containing the address addr1b) to host2, using
consider host2 deciding to add addr2b to the relationship. host2 now destination address addr2a, and a new set of SPIs would be added
has a choice to which of host1's addresses to initiate an UPDATE. It between hosts 1 and 2 (call them SPI1b and SPI2b-- not shown in the
may choose to initiate an UPDATE to addr1a, addr1b, or both. If it figure). Next, consider host2 deciding to add addr2b to the
chooses to send to both, then a full mesh (four SA pairs) of SAs relationship. Host2 must select one of host1's addresses towards
would exist between the two hosts. This is the most general case; it which to initiate an UPDATE. It may choose to initiate an UPDATE to
often may be the case that hosts primarily establish new SAs only addr1a, addr1b, or both. If it chooses to send to both, then a full
with the peer's preferred locator. The readdressing protocol is mesh (four SA pairs) of SAs would exist between the two hosts. This
flexible enough to accommodate this choice. is the most general case; it often may be the case that hosts
primarily establish new SAs only with the peer's Preferred locator.
The readdressing protocol is flexible enough to accommodate this
choice.
-<- SPI1a -- -- SPI2a ->- -<- SPI1a -- -- SPI2a ->-
host1 < > addr1a <---> addr2a < > host2 host1 < > addr1a <---> addr2a < > host2
->- SPI2a -- -- SPI1a -<- ->- SPI2a -- -- SPI1a -<-
addr1b <---> addr2a (second SA pair) addr1b <---> addr2a (second SA pair)
addr1a <---> addr2b (third SA pair) addr1a <---> addr2b (third SA pair)
addr1b <---> addr2b (fourth SA pair) addr1b <---> addr2b (fourth SA pair)
Figure 7: Dual multihoming case in which each host uses LOCATOR to Figure 6: Dual multihoming case in which each host uses LOCATOR to
add a second address add a second address
3.2.5. Combined mobility and multihoming 3.2.6. Combined mobility and multihoming
It looks likely that in the future many mobile hosts will be It looks likely that in the future many mobile hosts will be
simultaneously mobile and multi-homed, i.e., have multiple mobile simultaneously mobile and multi-homed, i.e., have multiple mobile
interfaces. Furthermore, if the interfaces use different access interfaces. Furthermore, if the interfaces use different access
technologies, it is fairly likely that one of the interfaces may technologies, it is fairly likely that one of the interfaces may
appear stable (retain its current IP address) while some other(s) may appear stable (retain its current IP address) while some other(s) may
experience mobility (undergo IP address change). experience mobility (undergo IP address change).
The use of LOCATOR plus ESP_INFO should be flexible enough to handle The use of LOCATOR plus ESP_INFO should be flexible enough to handle
most such scenarios, although more complicated scenarios have not most such scenarios, although more complicated scenarios have not
been studied so far. been studied so far.
3.2.6. Using LOCATORs across addressing realms 3.2.7. Using LOCATORs across addressing realms
It is possible for HIP associations to migrate to a state in which It is possible for HIP associations to migrate to a state in which
both parties are only using locators in different addressing realms. both parties are only using locators in different addressing realms.
For example, the two hosts may initiate the HIP association when both For example, the two hosts may initiate the HIP association when both
are using IPv6 locators, then one host may loose its IPv6 are using IPv6 locators, then one host may loose its IPv6
connectivity and obtain an IPv4 address. In such a case, some type connectivity and obtain an IPv4 address. In such a case, some type
of mechanism for interworking between the different realms must be of mechanism for interworking between the different realms must be
employed; such techniques are outside the scope of the present text. employed; such techniques are outside the scope of the present text.
If no mechanism exists, then the UPDATE message carrying the new The basic problem in this example is that the host readdressing to
LOCATOR will likely not reach the destination anyway, and the HIP IPv4 does not know a corresponding IPv4 address of the peer. This
state may time out. may be handled (experimentally) by possibly configuring this address
information manually or in the DNS, or the hosts exchange both IPv4
and IPv6 addresses in the locator.
3.2.7. Network renumbering 3.2.8. Network renumbering
It is expected that IPv6 networks will be renumbered much more often It is expected that IPv6 networks will be renumbered much more often
than most IPv4 networks are. From an end-host point of view, network than most IPv4 networks are. From an end-host point of view, network
renumbering is similar to mobility. renumbering is similar to mobility.
3.2.8. Initiating the protocol in R1 or I2 3.2.9. Initiating the protocol in R1 or I2
A Responder host MAY include one or more LOCATOR parameters in the R1 A Responder host MAY include a LOCATOR parameter in the R1 packet
packet that it sends to the Initiator. These parameters MUST be that it sends to the Initiator. This parameter MUST be protected by
protected by the R1 signature. If the R1 packet contains LOCATOR the R1 signature. If the R1 packet contains LOCATOR parameters with
parameters with a new preferred locator, the Initiator SHOULD a new Preferred locator, the Initiator SHOULD directly set the new
directly set the new preferred locator to status ACTIVE without Preferred locator to status ACTIVE without performing address
performing address verification first, and MUST send the I2 packet to verification first, and MUST send the I2 packet to the new Preferred
the new preferred locator. The I1 destination address and the new locator. The I1 destination address and the new Preferred locator
preferred locator may be identical. All new non-preferred locators may be identical. All new non-preferred locators must still undergo
must still undergo address verification. address verification once the base exchange completes.
Initiator Responder Initiator Responder
R1 with LOCATOR R1 with LOCATOR
<----------------------------------- <-----------------------------------
record additional addresses record additional addresses
change responder address change responder address
I2 sent to newly indicated preferred address I2 sent to newly indicated preferred address
-----------------------------------> ----------------------------------->
(process normally) (process normally)
R2 R2
<----------------------------------- <-----------------------------------
(process normally, later verification of non-preferred locators) (process normally, later verification of non-preferred locators)
Figure 8: LOCATOR inclusion in R1 Figure 7: LOCATOR inclusion in R1
An Initiator MAY include one or more LOCATOR parameters in the I2 An Initiator MAY include one or more LOCATOR parameters in the I2
packet, independent of whether there was a LOCATOR parameter in the packet, independent of whether there was a LOCATOR parameter in the
R1 or not. These parameters MUST be protected by the I2 signature. R1 or not. These parameters MUST be protected by the I2 signature.
Even if the I2 packet contains LOCATOR parameters, the Responder MUST Even if the I2 packet contains LOCATOR parameters, the Responder MUST
still send the R2 packet to the source address of the I2. The new still send the R2 packet to the source address of the I2. The new
preferred locator SHOULD be identical to the I2 source address. If Preferred locator SHOULD be identical to the I2 source address. If
the I2 packet contains LOCATOR parameters, all new locators must the I2 packet contains LOCATOR parameters, all new locators must
undergo address verification as usual. undergo address verification as usual, and the ESP traffic that
subsequently follows should use the Preferred locator.
Initiator Responder Initiator Responder
I2 with LOCATOR I2 with LOCATOR
-----------------------------------> ----------------------------------->
(process normally) (process normally)
record additional addresses record additional addresses
R2 sent to source address of I2 R2 sent to source address of I2
<----------------------------------- <-----------------------------------
(process normally) (process normally)
Figure 9: LOCATOR inclusion in I2 Figure 8: LOCATOR inclusion in I2
The I1 and I2 may be arriving from different source addresses if the
LOCATOR parameter is present in R1. In this case, implementations
using pre-created R1 indexed with IP addresses fail the puzzle
solution of I2 packets inadvertently. See, for example, the example
in Appendix A of [2]. As a solution, the responder's puzzle indexing
mechanism must be flexible enough to accomodate the situation when R1
includes a LOCATOR parameter.
3.3. Other Considerations 3.3. Other Considerations
3.3.1. Address Verification 3.3.1. Address Verification
When a HIP host receives a set of locators from another HIP host in a When a HIP host receives a set of locators from another HIP host in a
LOCATOR, it does not necessarily know whether the other host is LOCATOR, it does not necessarily know whether the other host is
actually reachable at the claimed addresses. In fact, a malicious actually reachable at the claimed addresses. In fact, a malicious
peer host may be intentionally giving bogus addresses in order to peer host may be intentionally giving bogus addresses in order to
cause a packet flood towards the target addresses [8]. Likewise, cause a packet flood towards the target addresses [9]. Likewise,
viral software may have compromised the peer host, programming it to viral software may have compromised the peer host, programming it to
redirect packets to the target addresses. Thus, the HIP host must redirect packets to the target addresses. Thus, the HIP host must
first check that the peer is reachable at the new address. first check that the peer is reachable at the new address.
An additional potential benefit of performing address verification is An additional potential benefit of performing address verification is
to allow middleboxes in the network along the new path to obtain the to allow middleboxes in the network along the new path to obtain the
peer host's inbound SPI. peer host's inbound SPI.
Address verification is implemented by the challenger sending some Address verification is implemented by the challenger sending some
piece of unguessable information to the new address, and waiting for piece of unguessable information to the new address, and waiting for
some acknowledgment from the responder that indicates reception of some acknowledgment from the responder that indicates reception of
the information at the new address. This may include exchange of a the information at the new address. This may include exchange of a
nonce, or generation of a new SPI and observing data arriving on the nonce, or generation of a new SPI and observing data arriving on the
new SPI. new SPI.
3.3.2. Credit-Based Authorization 3.3.2. Credit-Based Authorization
Credit-Based Authorization allows a host to securely use a new Credit-Based Authorization (CBA) allows a host to securely use a new
locator even though the peer's reachability at the address embedded locator even though the peer's reachability at the address embedded
in this locator has not yet been verified. This is accomplished in the locator has not yet been verified. This is accomplished based
based on the following three hypotheses: on the following three hypotheses:
1. A flooding attacker typically seeks to somehow multiply the 1. A flooding attacker typically seeks to somehow multiply the
packets it generates itself for the purpose of its attack because packets it generates for the purpose of its attack because
bandwidth is an ample resource for many attractive victims. bandwidth is an ample resource for many victims.
2. An attacker can always cause unamplified flooding by sending 2. An attacker can always cause unamplified flooding by sending
packets to its victim directly. packets to its victim directly.
3. Consequently, the additional effort required to set up a 3. Consequently, the additional effort required to set up a
redirection-based flooding attack would pay off for the attacker redirection-based flooding attack (without CBA and return
only if amplification could be obtained this way. routability checks) would pay off for the attacker only if
amplification could be obtained this way.
On this basis, rather than eliminating malicious packet redirection On this basis, rather than eliminating malicious packet redirection
in the first place, Credit-Based Authorization prevents any in the first place, Credit-Based Authorization prevents
amplification that can be reached through it. This is accomplished amplifications. This is accomplished by limiting the data a host can
by limiting the data a host can send to an unverified address of a send to an unverified address of a peer by the data recently received
peer by the data recently received from that peer. Redirection-based from that peer. Redirection-based flooding attacks thus become less
flooding attacks thus become less attractive than, e.g., pure direct attractive than, e.g., pure direct flooding, where the attacker
flooding, where the attacker itself sends bogus packets to the itself sends bogus packets to the victim.
victim.
Figure 10 illustrates Credit-Based Authorization: Host B measures the Figure 9 illustrates Credit-Based Authorization: Host B measures the
bytes recently received from peer A and, when A readdresses, sends amount of data recently received from peer A and, when A readdresses,
packets to A's new, unverified address as long as the sum of their sends packets to A's new, unverified address as long as the sum of
sizes does not exceed the measured, received data volume. When the packet sizes does not exceed the measured, received data volume.
insufficient credit is left, B stops sending further packets to A When insufficient credit is left, B stops sending further packets to
until A's address becomes ACTIVE. The address changes may be due to A until A's address becomes ACTIVE. The address changes may be due
mobility, due to multihoming, or due to any other reason. to mobility, due to multihoming, or due to any other reason. Not
shown in Figure 9 are the results of credit aging (Section 5.6.2), a
mechanism used to dampen possible time-shifting attacks.
+-------+ +-------+ +-------+ +-------+
| A | | B | | A | | B |
+-------+ +-------+ +-------+ +-------+
| | | |
address |------------------------->| credit += size(packet) address |------------------------------->| credit += size(packet)
ACTIVE | | ACTIVE | |
|------------------------->| credit += size(packet) |------------------------------->| credit += size(packet)
|<-------------------------| don't change credit |<-------------------------------| don't change credit
| | | |
+ address change | + address change |
address |<-------------------------| credit -= size(packet) + address verification starts |
UNVERIFIED |------------------------->| credit += size(packet) address |<-------------------------------| credit -= size(packet)
|<-------------------------| credit -= size(packet) UNVERIFIED |------------------------------->| credit += size(packet)
| | |<-------------------------------| credit -= size(packet)
|<-------------------------| credit -= size(packet)
| X credit < size(packet)=> drop!
| | | |
+ address change | |<-------------------------------| credit -= size(packet)
| X credit < size(packet)
| | => do not send packet!
+ address verification concludes |
address | | address | |
ACTIVE |<-------------------------| don't change credit ACTIVE |<-------------------------------| don't change credit
| | | |
Figure 10: Readdressing Scenario Figure 9: Readdressing Scenario
3.3.3. Preferred locator 3.3.3. Preferred locator
When a host has multiple locators, the peer host must decide upon When a host has multiple locators, the peer host must decide upon
which to use for outbound packets. It may be that a host would which to use for outbound packets. It may be that a host would
prefer to receive data on a particular inbound interface. HIP allows prefer to receive data on a particular inbound interface. HIP allows
a particular locator to be designated as a preferred locator, and a particular locator to be designated as a Preferred locator, and
communicated to the peer (see Section 4). communicated to the peer (see Section 4).
In general, when multiple locators are used for a session, there is In general, when multiple locators are used for a session, there is
the question of using multiple locators for failover only or for the question of using multiple locators for failover only or for
load-balancing. Due to the implications of load-balancing on the load-balancing. Due to the implications of load-balancing on the
transport layer that still need to be worked out, this draft assumes transport layer that still need to be worked out, this draft assumes
that multiple locators are used primarily for failover. An that multiple locators are used primarily for failover. An
implementation may use ICMP interactions, reachability checks, or implementation may use ICMP interactions, reachability checks, or
other means to detect the failure of a locator. other means to detect the failure of a locator.
3.3.4. Interaction with Security Associations 3.3.4. Interaction with Security Associations
This document specifies a new HIP protocol parameter, the LOCATOR This document specifies a new HIP protocol parameter, the LOCATOR
parameter (see Section 4), that allows the hosts to exchange parameter (see Section 4), that allows the hosts to exchange
information about their locator(s), and any changes in their information about their locator(s), and any changes in their
locator(s). The logical structure created with LOCATOR parameters locator(s). The logical structure created with LOCATOR parameters
has three levels: hosts, Security Associations (SAs) indexed by has three levels: hosts, Security Associations (SAs) indexed by
Security Parameter Indices (SPIs), and addresses. Security Parameter Indices (SPIs), and addresses.
The relation between these entities for an association negotiated as The relation between these levels for an association constructed as
defined in the base specification [2] and ESP transform [5] is defined in the base specification [2] and ESP transform [6] is
illustrated in Figure 11. illustrated in Figure 10.
-<- SPI1a -- -- SPI2a ->- -<- SPI1a -- -- SPI2a ->-
host1 < > addr1a <---> addr2a < > host2 host1 < > addr1a <---> addr2a < > host2
->- SPI2a -- -- SPI1a -<- ->- SPI2a -- -- SPI1a -<-
Figure 11: Relation between hosts, SPIs, and addresses (base Figure 10: Relation between hosts, SPIs, and addresses (base
specification) specification)
In Figure 11, host1 and host2 negotiate two unidirectional SAs, and In Figure 10, host1 and host2 negotiate two unidirectional SAs, and
each host selects the SPI value for its inbound SA. The addresses each host selects the SPI value for its inbound SA. The addresses
addr1a and addr2a are the source addresses that each host uses in the addr1a and addr2a are the source addresses that the hosts use in the
base HIP exchange. These are the "preferred" (and only) addresses base HIP exchange. These are the "preferred" (and only) addresses
conveyed to the peer for each SA; even though packets sent to any of conveyed to the peer for use on each SA. That is, although packets
the hosts' interfaces can arrive on an inbound SPI, when a host sends sent to any of the hosts' interfaces may be accepted on the inbound
packets to the peer on an outbound SPI, it knows of a single SA, the peer host in general knows of only the single destination
destination address associated with that outbound SPI (for host1, it address learned in the base exchange (e.g., for host1, it sends a
sends a packet on SPI2a to addr2a to reach host2), unless other packet on SPI2a to addr2a to reach host2), unless other mechanisms
mechanisms exist to learn of new addresses. exist to learn of new addresses.
In general, the bindings that exist in an implementation In general, the bindings that exist in an implementation
corresponding to this draft can be depicted as shown in Figure 12. corresponding to this draft can be depicted as shown in Figure 11.
In this figure, a host can have multiple inbound SPIs (and, not In this figure, a host can have multiple inbound SPIs (and, not
shown, multiple outbound SPIs) between itself and another host. shown, multiple outbound SPIs) associated with another host.
Furthermore, each SPI may have multiple addresses associated with it. Furthermore, each SPI may have multiple addresses associated with it.
These addresses bound to an SPI are not used as SA selectors. These addresses bound to an SPI are not used to lookup the incoming
Rather, the addresses are those addresses that are provided to the SA. Rather, the addresses are those addresses that are provided to
peer host, as hints for which addresses to use to reach the host on the peer host, as hints for which addresses to use to reach the host
that SPI. The LOCATOR parameter allows for IP addresses and SPIs to on that SPI. The LOCATOR parameter is used to change the set of
be combined to form generalized locators. The LOCATOR parameter is addresses that a peer associates with a particular SPI.
used to change the set of addresses that a peer associates with a
particular SPI.
address11 address11
/ /
SPI1 - address12 SPI1 - address12
/ /
/ address21 / address21
host -- SPI2 < host -- SPI2 <
\ address22 \ address22
\ \
SPI3 - address31 SPI3 - address31
\ \
address32 address32
Figure 12: Relation between hosts, SPIs, and addresses (general case) Figure 11: Relation between hosts, SPIs, and addresses (general case)
A host may establish any number of security associations (or SPIs) A host may establish any number of security associations (or SPIs)
with a peer. The main purpose of having multiple SPIs is to group with a peer. The main purpose of having multiple SPIs with a peer is
the addresses into collections that are likely to experience fate to group the addresses into collections that are likely to experience
sharing. For example, if the host needs to change its addresses on fate sharing. For example, if the host needs to change its addresses
SPI2, it is likely that both address21 and address22 will on SPI2, it is likely that both address21 and address22 will
simultaneously become obsolete. In a typical case, such SPIs may simultaneously become obsolete. In a typical case, such SPIs may
correspond with physical interfaces; see below. Note, however, that correspond with physical interfaces; see below. Note, however, that
especially in the case of site multihoming, one of the addresses may especially in the case of site multihoming, one of the addresses may
become unreachable while the other one still works. In the typical become unreachable while the other one still works. In the typical
case, however, this does not require the host to inform its peers case, however, this does not require the host to inform its peers
about the situation, since even the non-working address still about the situation, since even the non-working address still
logically exists. logically exists.
A basic property of HIP SAs is that the inbound IP address is not A basic property of HIP SAs is that the inbound IP address is not
used as a selector for the SA. Therefore, in Figure 12, it may seem used to lookup the incoming SA. Therefore, in Figure 11, it may seem
unnecessary for address31, for example, to be associated only with unnecessary for address31, for example, to be associated only with
SPI3-- in practice, a packet may arrive to SPI1 via destination SPI3-- in practice, a packet may arrive to SPI1 via destination
address address31 as well. However, the use of different source and address address31 as well. However, the use of different source and
destination addresses typically leads to different paths, with destination addresses typically leads to different paths, with
different latencies in the network, and if packets were to arrive via different latencies in the network, and if packets were to arrive via
an arbitrary destination IP address (or path) for a given SPI, the an arbitrary destination IP address (or path) for a given SPI, the
reordering due to different latencies may cause some packets to fall reordering due to different latencies may cause some packets to fall
outside of the ESP anti-replay window. For this reason, HIP provides outside of the ESP anti-replay window. For this reason, HIP provides
a mechanism to affiliate destination addresses with inbound SPIs, if a mechanism to affiliate destination addresses with inbound SPIs,
there is a concern that anti-replay windows might be violated when there is a concern that anti-replay windows might be violated.
otherwise. In this sense, we can say that a given inbound SPI has an In this sense, we can say that a given inbound SPI has an "affinity"
"affinity" for certain inbound IP addresses, and this affinity is for certain inbound IP addresses, and this affinity is communicated
communicated to the peer host. Each physical interface SHOULD have a to the peer host. Each physical interface SHOULD have a separate SA,
separate SA, unless the ESP anti-replay window is loose. unless the ESP anti-replay window is loose.
Moreover, even if the destination addresses used for a particular SPI Moreover, even when the destination addresses used for a particular
are held constant, the use of different source interfaces may also SPI are held constant, the use of different source interfaces may
cause packets to fall outside of the ESP anti-replay window, since also cause packets to fall outside of the ESP anti-replay window,
the path traversed is often affected by the source address or since the path traversed is often affected by the source address or
interface used. A host has no way to influence the source interface interface used. A host has no way to influence the source interface
on which a peer uses to send its packets on a given SPI. Hosts on which a peer sends its packets on a given SPI. A host SHOULD
SHOULD consistently use the same source interface and address when consistently use the same source interface and address when sending
sending to a particular destination IP address and SPI. For this to a particular destination IP address and SPI. For this reason, a
reason, a host may find it useful to change its SPI or at least reset host may find it useful to change its SPI or at least reset its ESP
its ESP anti-replay window when the peer host readdresses. anti-replay window when the peer host readdresses.
An address may appear on more than one SPI. This creates no An address may appear on more than one SPI. This creates no
ambiguity since the receiver will ignore the IP addresses as SA ambiguity since the receiver will ignore the IP addresses during SA
selectors anyway. However, this document does not specify such lookup anyway. However, this document does not specify such cases.
cases.
If the LOCATOR parameter is sent in an UPDATE packet, then the When the LOCATOR parameter is sent in an UPDATE packet, then the
receiver will respond with an UPDATE acknowledgment. If the LOCATOR receiver will respond with an UPDATE acknowledgment. When the
parameter is sent in a NOTIFY, I2, or R2 packet, then the recipient LOCATOR parameter is sent in an R1 or I2 packet, the base exchange
may consider the LOCATOR as informational, and act only when it needs retransmission mechanism will confirm its successful delivery.
to activate a new address. The use of LOCATOR in a NOTIFY message LOCATORs may experimentally be used in NOTIFY packets; in this case,
may not be compatible with middleboxes. the recipient MUST consider the LOCATOR as informational and not
immediately change the current preferred address, but can test the
additional locators when the need arises. The use of LOCATOR in a
NOTIFY message may not be compatible with middleboxes.
4. LOCATOR parameter format 4. LOCATOR parameter format
The LOCATOR parameter is a critical parameter as defined by [2]. It The LOCATOR parameter is a critical parameter as defined by [2]. It
consists of the standard HIP parameter Type and Length fields, plus consists of the standard HIP parameter Type and Length fields, plus
one or more Locator sub-parameters. Each Locator sub-parameter zero or more Locator sub-parameters. Each Locator sub-parameter
contains a Traffic Type, Locator Type, Locator Length, Preferred contains a Traffic Type, Locator Type, Locator Length, Preferred
Locator bit, Locator Lifetime, and a Locator encoding. locator bit, Locator Lifetime, and a Locator encoding. A LOCATOR
contaning zero Locator fields is permitted but has the effect of
DEPRECATING all addresses.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Type | Locator Type | Locator Length | Reserved |P| | Traffic Type | Locator Type | Locator Length | Reserved |P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Locator Lifetime | | Locator Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 24, line 6 skipping to change at page 24, line 8
Length: Length in octets, excluding Type and Length fields, and Length: Length in octets, excluding Type and Length fields, and
excluding padding. excluding padding.
Traffic Type: Defines whether the locator pertains to HIP signaling, Traffic Type: Defines whether the locator pertains to HIP signaling,
user data, or both. user data, or both.
Locator Type: Defines the semantics of the Locator field. Locator Type: Defines the semantics of the Locator field.
Locator Length: Defines the length of the Locator field, in units of Locator Length: Defines the length of the Locator field, in units of
4-byte words (Locators up to a maximum of 4*255 bytes are 4-byte words (Locators up to a maximum of 4*255 octets are
supported). supported).
Reserved: Zero when sent, ignored when received. Reserved: Zero when sent, ignored when received.
P: Preferred locator. Set to one if the locator is preferred for P: Preferred locator. Set to one if the locator is preferred for
that Traffic Type; otherwise set to zero. that Traffic Type; otherwise set to zero.
Locator Lifetime: Locator lifetime, in seconds. Locator Lifetime: Locator lifetime, in seconds.
Locator: The locator whose semantics and encoding are indicated by Locator: The locator whose semantics and encoding are indicated by
the Locator Type field. All Locator sub-fields are integral the Locator Type field. All Locator sub-fields are integral
multiples of four bytes in length. multiples of four octets in length.
The Locator Lifetime indicates how long the following locator is The Locator Lifetime indicates how long the following locator is
expected to be valid. The lifetime is expressed in seconds. Each expected to be valid. The lifetime is expressed in seconds. Each
locator MUST have a non-zero lifetime. The address is expected to locator MUST have a non-zero lifetime. The address is expected to
become deprecated when the specified number of seconds has passed become deprecated when the specified number of seconds has passed
since the reception of the message. A deprecated address SHOULD NOT since the reception of the message. A deprecated address SHOULD NOT
be used as an destination address if an alternate (non-deprecated) is be used as an destination address if an alternate (non-deprecated) is
available and has sufficient scope. available and has sufficient scope.
4.1. Traffic Type and Preferred Locator 4.1. Traffic Type and Preferred locator
The following Traffic Type values are defined: The following Traffic Type values are defined:
0: Both signaling (HIP control packets) and user data. 0: Both signaling (HIP control packets) and user data.
1: Signaling packets only. 1: Signaling packets only.
2: Data packets only. 2: Data packets only.
The "P" bit, when set, has scope over the corresponding Traffic Type The "P" bit, when set, has scope over the corresponding Traffic Type.
that precedes it. That is, if a "P" bit is set for Traffic Type "2", That is, when a "P" bit is set for Traffic Type "2", for example, it
for example, that means that the locator is preferred for data means that the locator is preferred for data packets. If there is a
packets. If there is a conflict (for example, if P bit is set for an conflict (for example, if P bit is set for an address of Type "0" and
address of Type "0" and a different address of Type "2"), the more a different address of Type "2"), the more specific Traffic Type rule
specific Traffic Type rule applies. By default, the IP addresses applies (in this case, "2"). By default, the IP addresses used in
used in the base exchange are preferred locators for both signaling the base exchange are Preferred locators for both signaling and user
and user data, unless a new preferred locator supersedes them. If no data, unless a new Preferred locator supersedes them. If no locators
locators are indicated as preferred for a given Traffic Type, the are indicated as preferred for a given Traffic Type, the
implementation may use an arbitrary locator from the set of active implementation may use an arbitrary locator from the set of active
locators. locators.
4.2. Locator Type and Locator 4.2. Locator Type and Locator
The following Locator Type values are defined, along with the The following Locator Type values are defined, along with the
associated semantics of the Locator field: associated semantics of the Locator field:
0: An IPv6 address or an IPv4-in-IPv6 format IPv4 address [7] (128 0: An IPv6 address or an IPv4-in-IPv6 format IPv4 address [8] (128
bits long). bits long). This locator type is defined primarily for non-ESP-
based usage.
1: The concatenation of an ESP SPI (first 32 bits) followed by an 1: The concatenation of an ESP SPI (first 32 bits) followed by an
IPv6 address or an IPv4-in-IPv6 format IPv4 address (an additional IPv6 address or an IPv4-in-IPv6 format IPv4 address (an additional
128 bits). 128 bits). This IP address is defined primarily for ESP-based
usage.
4.3. UPDATE packet with included LOCATOR 4.3. UPDATE packet with included LOCATOR
A number of combinations of parameters in an UPDATE packet are A number of combinations of parameters in an UPDATE packet are
possible (e.g., see Section 3.2). Only one LOCATOR parameter is used possible (e.g., see Section 3.2). In this document, procedures are
in any HIP packet, and this LOCATOR SHOULD list all of the locators defined only for the case in which one LOCATOR and one ESP_INFO
that the host wishes to make available for the HIP association. Any parameter is used in any HIP packet. Furthermore, the LOCATOR SHOULD
list all of the locators that are active on the HIP association
(including those on SAs not covered by the ESP_INFO parameter). Any
UPDATE packet that includes a LOCATOR parameter SHOULD include both UPDATE packet that includes a LOCATOR parameter SHOULD include both
an HMAC and a HIP_SIGNATURE parameter. an HMAC and a HIP_SIGNATURE parameter. The relationship between the
announced Locators and any ESP_INFO parameters present in the packet
is defined in Section 5.2. The sending of multiple LOCATOR and/or
ESP_INFO parameters is for further study; receivers may wish to
experiment with supporting such a possibility.
5. Processing rules 5. Processing rules
This section describes rules for sending and receiving the LOCATOR
parameter, testing address reachability, and using Credit-Based
Authorization (CBA) on UNVERIFIED locators.
5.1. Locator data structure and status 5.1. Locator data structure and status
In a typical implementation, each outgoing locator is represented by In a typical implementation, each outgoing locator is represented by
a piece of state that contains the following data: a piece of state that contains the following data:
o the actual bit pattern representing the locator, o the actual bit pattern representing the locator,
o lifetime (seconds), o lifetime (seconds),
o status (UNVERIFIED, ACTIVE, DEPRECATED). o status (UNVERIFIED, ACTIVE, DEPRECATED).
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A DEPRECATED address MUST NOT be changed to ACTIVE without first A DEPRECATED address MUST NOT be changed to ACTIVE without first
verifying its reachability. verifying its reachability.
5.2. Sending LOCATORs 5.2. Sending LOCATORs
The decision of when to send LOCATORs is basically a local policy The decision of when to send LOCATORs is basically a local policy
issue. However, it is RECOMMENDED that a host sends a LOCATOR issue. However, it is RECOMMENDED that a host sends a LOCATOR
whenever it recognizes a change of its IP addresses in use on an whenever it recognizes a change of its IP addresses in use on an
active HIP association, and assumes that the change is going to last active HIP association, and assumes that the change is going to last
at least for a few seconds. Rapidly sending conflicting LOCATORs at least for a few seconds. Rapidly sending LOCATORs that force the
SHOULD be avoided. peer to change the preferred address SHOULD be avoided.
When a host decides to inform its peers about changes in its IP When a host decides to inform its peers about changes in its IP
addresses, it has to decide how to group the various addresses with addresses, it has to decide how to group the various addresses with
SPIs. The grouping should consider also whether middlebox SPIs. The grouping should consider also whether middlebox
interaction requires sending (the same) LOCATOR in separate UPDATEs interaction requires sending (the same) LOCATOR in separate UPDATEs
on different paths. Since each SPI is associated with a different on different paths. Since each SPI is associated with a different
Security Association, the grouping policy may also be based on ESP Security Association, the grouping policy may also be based on ESP
anti-replay protection considerations. In the typical case, simply anti-replay protection considerations. In the typical case, simply
basing the grouping on actual kernel level physical and logical basing the grouping on actual kernel level physical and logical
interfaces may be the best policy. Grouping policy is outside of the interfaces may be the best policy. Grouping policy is outside of the
skipping to change at page 27, line 31 skipping to change at page 27, line 35
Note that the purpose of announcing IP addresses in a LOCATOR is to Note that the purpose of announcing IP addresses in a LOCATOR is to
provide connectivity between the communicating hosts. In most cases, provide connectivity between the communicating hosts. In most cases,
tunnels or virtual interfaces such as IPsec tunnel interfaces or tunnels or virtual interfaces such as IPsec tunnel interfaces or
Mobile IP home addresses provide sub-optimal connectivity. Mobile IP home addresses provide sub-optimal connectivity.
Furthermore, it should be possible to replace most tunnels with HIP Furthermore, it should be possible to replace most tunnels with HIP
based "non-tunneling", therefore making most virtual interfaces based "non-tunneling", therefore making most virtual interfaces
fairly unnecessary in the future. Therefore, virtual interfaces fairly unnecessary in the future. Therefore, virtual interfaces
SHOULD NOT be announced in general. On the other hand, there are SHOULD NOT be announced in general. On the other hand, there are
clearly situations where tunnels are used for diagnostic and/or clearly situations where tunnels are used for diagnostic and/or
testing purposes. In such and other similar cases announcing the IP testing purposes. In such and other similar cases announcing the IP
addresses of virtual interfaces may be appropriate. addresses of virtual interfaces may be appropriate. Hosts MUST NOT
announce broadcast or multicast addresses in LOCATORs. The
announcement of link-local addresses is a policy decision; such
addresses used as Preferred locators will create reachability
problems when the host moves to another link.
Once the host has decided on the groups and assignment of addresses Once the host has decided on the groups and assignment of addresses
to the SPIs, it creates a LOCATOR parameter that serves as a complete to the SPIs, it creates a LOCATOR parameter that serves as a complete
representation of the addresses and affiliated SPIs intended for representation of the addresses and affiliated SPIs intended for
active use. We now describe a few cases introduced in Section 3.2. active use. We now describe a few cases introduced in Section 3.2.
We assume that the Traffic Type for each locator is set to "0" (other We assume that the Traffic Type for each locator is set to "0" (other
values for Traffic Type may be specified in documents that separate values for Traffic Type may be specified in documents that separate
HIP control plane from data plane traffic). Other mobility and HIP control plane from data plane traffic). Other mobility and
multihoming cases are possible but are left for further multihoming cases are possible but are left for further
experimentation. experimentation.
skipping to change at page 28, line 20 skipping to change at page 28, line 27
contains the current value of the SPI in the "Old SPI" and the contains the current value of the SPI in the "Old SPI" and the
new value of the SPI in the "New SPI", and a "Keymat Index" as new value of the SPI in the "New SPI", and a "Keymat Index" as
selected by local policy. Optionally, the host may choose to selected by local policy. Optionally, the host may choose to
initiate a Diffie Hellman rekey by including a DIFFIE_HELLMAN initiate a Diffie Hellman rekey by including a DIFFIE_HELLMAN
parameter. The LOCATOR contains a single Locator with "Locator parameter. The LOCATOR contains a single Locator with "Locator
Type" of "1"; the SPI must match that of the "New SPI" in the Type" of "1"; the SPI must match that of the "New SPI" in the
ESP_INFO. Otherwise, the steps are identical to the case when no ESP_INFO. Otherwise, the steps are identical to the case when no
rekeying is initiated. rekeying is initiated.
3. Host multihoming (addition of an address). We only describe the 3. Host multihoming (addition of an address). We only describe the
simple case of adding an additional address to a single-homed, simple case of adding an additional address to a (previously)
non-mobile host. The host SHOULD set up a new SA pair between single-homed, non-mobile host. The host SHOULD set up a new SA
this new address and the preferred address of the peer host. To pair between this new address and the preferred address of the
do this, the multihomed host creates a new inbound SA and creates peer host. To do this, the multihomed host creates a new inbound
a new ESP_INFO parameter with an "Old SPI" parameter of "0", a SA and creates a new SPI. For the outgoing UPDATE message, it
"New SPI" parameter corresponding to the new SPI, and a "Keymat inserts an ESP_INFO parameter with an "Old SPI" field of "0", a
"New SPI" field corresponding to the new SPI, and a "Keymat
Index" as selected by local policy. The host adds to the UPDATE Index" as selected by local policy. The host adds to the UPDATE
message a LOCATOR with two Type "1" Locators: the original message a LOCATOR with two Type "1" Locators: the original
address and SPI active on the association, and the new address address and SPI active on the association, and the new address
and new SPI being added (with the SPI matching the "New SPI" and new SPI being added (with the SPI matching the "New SPI"
contained in the ESP_INFO). The Preferred bit SHOULD be set contained in the ESP_INFO). The Preferred bit SHOULD be set
depending on the policy to tell the peer host which of the two depending on the policy to tell the peer host which of the two
locators is preferred. The UPDATE also contains a SEQ parameter locators is preferred. The UPDATE also contains a SEQ parameter
and optionally a DIFFIE_HELLMAN parameter, and follows rekeying and optionally a DIFFIE_HELLMAN parameter, and follows rekeying
procedures with respect to this new address. The UPDATE message procedures with respect to this new address. The UPDATE message
SHOULD be sent to the peer's preferred address with a source SHOULD be sent to the peer's Preferred address with a source
address corresponding to the new locator. address corresponding to the new locator.
The sending of multiple LOCATORs, locators with Locator Type "0", and The sending of multiple LOCATORs, locators with Locator Type "0", and
multiple ESP_INFO parameters is for further study. multiple ESP_INFO parameters is for further study. Note that the
inclusion of LOCATOR in an R1 packet requires the use of Type "0"
locators since no SAs are set up at that point.
5.3. Handling received LOCATORs 5.3. Handling received LOCATORs
A host SHOULD be prepared to receive a LOCATOR parameter in any HIP A host SHOULD be prepared to receive a LOCATOR parameter in the
packet, excluding I1. following HIP packets: R1, I2, UPDATE, and NOTIFY.
This document describes sending both ESP_INFO and LOCATOR parameters This document describes sending both ESP_INFO and LOCATOR parameters
in an UPDATE. The ESP_INFO parameter is included if there is a need in an UPDATE. The ESP_INFO parameter is included when there is a
to rekey or key a new SPI, and is otherwise included for the possible need to rekey or key a new SPI, and is otherwise included for the
benefit of HIP-aware middleboxes. The LOCATOR parameter contains a possible benefit of HIP-aware middleboxes. The LOCATOR parameter
complete map of the locators that the host wishes to make or keep contains a complete map of the locators that the host wishes to make
active for the HIP association. or keep active for the HIP association.
In general, the processing of a LOCATOR depends upon the packet type In general, the processing of a LOCATOR depends upon the packet type
in which it is included and upon whether ESP_INFO parameter is in which it is included. Here, we describe only the case in which
included. Here, we describe only the case in which ESP_INFO is ESP_INFO is present and a single LOCATOR and ESP_INFO are sent in an
present and a single LOCATOR and ESP_INFO are sent in an UPDATE UPDATE message; other cases are for further study. The steps below
message; other cases are for further study. The steps below cover cover each of the cases described in Section 5.2.
each of the cases described in Section 5.2.
When a host receives a LOCATOR parameter in a validated HIP packet, The processing of ESP_INFO and LOCATOR parameters is intended to be
it first performs the following operations: modular and support future generalization to the inclusion of
multiple ESP_INFO and/or multiple LOCATOR parameters. A host SHOULD
first process the ESP_INFO before the LOCATOR, since the ESP_INFO may
contain a new SPI value mapped to an existing SPI, while a Type 1
locator will only contain reference to the new SPI.
1. The host checks if the New SPI listed in the ESP_INFO is a new When a host receives a validated HIP UPDATE with a LOCATOR and
one. If it is a new one, it creates a new inbound SA with that ESP_INFO parameter, it processes the ESP_INFO as follows. The
SPI that contains no addresses. If it is an existing one, it ESP_INFO parameter indicates whether a SA is being rekeyed, created,
prepares to change the address set on the existing SPI. deprecated, or just identified for the benefit of middleboxes. The
host examines the Old SPI and New SPI values in the ESP_INFO
parameter:
2. For each locator listed in the LOCATOR parameter, check that the 1. (no rekeying) If the Old SPI is equal to the New SPI and both
address therein is a legal unicast or anycast address. That is, correspond to an existing SPI, the ESP_INFO is gratuitous
the address MUST NOT be a broadcast or multicast address. Note (provided for middleboxes) and no rekeying is necessary.
that some implementations MAY accept addresses that indicate the
local host, since it may be allowed that the host runs HIP with
itself.
3. For each Type 1 address listed in the LOCATOR parameter, check if 2. (rekeying) If the Old SPI indicates an existing SPI and the New
the address is already bound to the SPI indicated. If the SPI is a different non-zero value, the existing SA is being
address is already bound, its lifetime is updated. If the status rekeyed and the host follows HIP ESP rekeying procedures by
of the address is DEPRECATED, the status is changed to creating a new outbound SA with an SPI corresponding to the New
UNVERIFIED. If the address is not already bound, the address is SPI, with no addresses bound to this SPI. Note that locators in
added, and its status is set to UNVERIFIED. Mark all addresses the LOCATOR parameter will reference this new SPI instead of the
on the SPI that were NOT listed in the LOCATOR parameter as old SPI.
DEPRECATED. As a result, the SPI now contains any addresses
listed in the LOCATOR parameter either as UNVERIFIED or ACTIVE,
and any old addresses not listed in the LOCATOR parameter as
DEPRECATED.
4. If the LOCATOR is paired with an ESP_INFO parameter, the ESP_INFO 3. (new SA) If the Old SPI value is zero and the New SPI is a new
parameter is processed as follows: non-zero value, then a new SA is being requested by the peer.
This case is also treated like a rekeying event; the receiving
host must create a new SA and respond with an UPDATE ACK.
1. If the Old SPI indicates an existing SPI and the New SPI is a 4. (deprecating of SA) If the Old SPI indicates an existing SPI and
different non-zero value, the existing SA is being rekeyed the New SPI is zero, the SA is being deprecated and all locators
and the host follows HIP ESP rekeying procedures. Note that uniquely bound to the SPI are put into DEPRECATED state.
the Locators in the LOCATOR parameter will use this New SPI
instead of the Old SPI.
2. If the Old SPI value is zero and the New SPI is a new non- If none of the above cases apply, a protocol error has occurred and
zero value, then a new SA is being requested by the peer. the processing of the UPDATE is stopped.
This case is also treated like a rekeying event; the
receiving host must create a new inbound SA and respond with
an UPDATE ACK.
3. If the Old SPI indicates an existing SPI and the New SPI is Next, the locators in the LOCATOR parameter are processed. For each
zero, the SPI is being deprecated and all locators uniquely locator listed in the LOCATOR parameter, check that the address
bound to the SPI are put into DEPRECATED state. therein is a legal unicast or anycast address. That is, the address
MUST NOT be a broadcast or multicast address. Note that some
implementations MAY accept addresses that indicate the local host,
since it may be allowed that the host runs HIP with itself.
4. If the Old SPI equals the New SPI and both correspond to an The below assumes that all locators are of Type 1 with a Traffic Type
existing SPI, the ESP_INFO is gratuitous (provided for of 0; other cases are for further study.
middleboxes) and no rekeying is necessary.
5. Mark all locators on each SPI that were NOT listed in the LOCATOR For each Type 1 address listed in the LOCATOR parameter, the host
parameter as DEPRECATED. checks whether the address is already bound to the SPI indicated. If
the address is already bound, its lifetime is updated. If the status
of the address is DEPRECATED, the status is changed to UNVERIFIED.
If the address is not already bound, the address is added, and its
status is set to UNVERIFIED. Mark all addresses corresponding to the
SPI that were NOT listed in the LOCATOR parameter as DEPRECATED.
As a result, each SPI now contains any addresses listed in the As a result, at the end of processing, the addresses listed in the
LOCATOR parameter either as UNVERIFIED or ACTIVE, and any old LOCATOR parameter have either a state of UNVERIFIED or ACTIVE, and
addresses not listed in the LOCATOR parameter as DEPRECATED. any old addresses on the old SA not listed in the LOCATOR parameter
have a state of DEPRECATED.
Once the host has updated the SPI, if the LOCATOR parameter contains Once the host has processed the locators, if the LOCATOR parameter
a new preferred locator, the host SHOULD initiate a change of the contains a new Preferred locator, the host SHOULD initiate a change
preferred locator. This requires that the host first verifies of the Preferred locator. This requires that the host first verifies
reachability of the associated address, and only then changes the reachability of the associated address, and only then changes the
preferred locator. See Section 5.6. Preferred locator. See Section 5.5.
5.4. Verifying address reachability 5.4. Verifying address reachability
A host MUST verify the reachability of an UNVERIFIED address. The A host MUST verify the reachability of an UNVERIFIED address. The
status of a newly learned address MUST initially be set to UNVERIFIED status of a newly learned address MUST initially be set to UNVERIFIED
unless the new address is advertised in a R1 packet as a new unless the new address is advertised in a R1 packet as a new
preferred locator. A host MAY also want to verify the reachability Preferred locator. A host MAY also want to verify the reachability
of an ACTIVE address again after some time, in which case it would of an ACTIVE address again after some time, in which case it would
set the status of the address to UNVERIFIED and reinitiate address set the status of the address to UNVERIFIED and reinitiate address
verification verification
A host typically starts the address-verification procedure by sending A host typically starts the address-verification procedure by sending
a nonce to the new address. For example, if the host is changing its a nonce to the new address. For example, when the host is changing
SPI and is sending an ESP_INFO to the peer, the new SPI value SHOULD its SPI and is sending an ESP_INFO to the peer, the new SPI value
be random and the value MAY be copied into an ECHO_REQUEST sent in SHOULD be random and the value MAY be copied into an ECHO_REQUEST
the rekeying UPDATE. If the host is not rekeying, it MAY still use sent in the rekeying UPDATE. However, if the host is not changing
the ECHO_REQUEST parameter in an UPDATE message sent to the new its SPI, it MAY still use the ECHO_REQUEST parameter in an UPDATE
address. A host MAY also use other message exchanges as confirmation message sent to the new address. A host MAY also use other message
of the address reachability. exchanges as confirmation of the address reachability.
Note that in the case of receiving a LOCATOR on an R1 and replying Note that in the case of receiving a LOCATOR in an R1 and replying
with an I2, receiving the corresponding R2 is sufficient proof of with an I2 to the new address in the LOCATOR, receiving the
reachability for the Responder's preferred address. Since further corresponding R2 is sufficient proof of reachability for the
address verification of such address can impede the HIP base Responder's preferred address. Since further address verification of
exchange, a host MUST NOT verify reachability of a new preferred such address can impede the HIP base exchange, a host MUST NOT
locator that was received on a R1. separately verify reachability of a new Preferred locator that was
received on a R1.
In some cases, it may be sufficient to use the arrival of data on a In some cases, it MAY be sufficient to use the arrival of data on a
newly advertised SA as implicit address reachability verification, newly advertised SA as implicit address reachability verification as
instead of waiting for the confirmation via a HIP packet (e.g., depicted in Figure 13, instead of waiting for the confirmation via a
Figure 14). In this case, a host advertising a new SPI as part of HIP packet. In this case, a host advertising a new SPI as part of
its address reachability check SHOULD be prepared to receive traffic its address reachability check SHOULD be prepared to receive traffic
on the new SA. Marking the address ACTIVE as a part of receiving on the new SA.
data on the SA is an idempotent operation, and does not cause any
harm.
Mobile host Peer host Mobile host Peer host
prepare incoming SA prepare incoming SA
new SPI in R2, or UPDATE new SPI in ESP_INFO (UPDATE)
<----------------------------------- <-----------------------------------
switch to new outgoing SA switch to new outgoing SA
data on new SA data on new SA
-----------------------------------> ----------------------------------->
mark address ACTIVE mark address ACTIVE
Figure 14: Address activation via use of new SA Figure 13: Address activation via use of new SA
When address verification is in progress for a new preferred locator, When address verification is in progress for a new Preferred locator,
the host SHOULD select a different locator listed as ACTIVE, if one the host SHOULD select a different locator listed as ACTIVE, if one
such locator is available, to continue communications until address such locator is available, to continue communications until address
verification completes. Alternatively, the host MAY use the new verification completes. Alternatively, the host MAY use the new
preferred locator while in UNVERIFIED status to the extent Credit- Preferred locator while in UNVERIFIED status to the extent Credit-
Based Authorization permits. Credit-Based Authorization is explained Based Authorization permits. Credit-Based Authorization is explained
in Section 5.5. Once address verification succeeds, the status of in Section 5.6. Once address verification succeeds, the status of
the new preferred locator changes to ACTIVE. the new Preferred locator changes to ACTIVE.
5.5. Credit-Based Authorization 5.5. Changing the Preferred locator
5.5.1. Handling Payload Packets A host MAY want to change the Preferred outgoing locator for
different reasons, e.g., because traffic information or ICMP error
messages indicate that the currently used preferred address may have
become unreachable. Another reason may be due to receiving a LOCATOR
parameter that has the P-bit set.
To change the Preferred locator, the host initiates the following
procedure:
1. If the new Preferred locator has ACTIVE status, the Preferred
locator is changed and the procedure succeeds.
2. If the new Preferred locator has UNVERIFIED status, the host
starts to verify its reachability. The host SHOULD use a
different locator listed as ACTIVE until address verification
completes if one such locator is available. Alternatively, the
host MAY use the new Preferred locator, even though in UNVERIFIED
status, to the extent Credit-Based Authorization permits. Once
address verification succeeds, the status of the new Preferred
locator changes to ACTIVE and its use is no longer governed by
Credit-Based Authorization.
3. If the peer host has not indicated a preference for any address,
then the host picks one of the peer's ACTIVE addresses randomly
or according to policy. This case may arise if, for example,
ICMP error messages arrive that deprecate the Preferred locator,
but the peer has not yet indicated a new Preferred locator.
4. If the new Preferred locator has DEPRECATED status and there is
at least one non-deprecated address, the host selects one of the
non-deprecated addresses as a new Preferred locator and
continues. If the selected address is UNVERIFIED, this includes
address verification as described above.
5.6. Credit-Based Authorization
To prevent redirection-based flooding attacks, the use of a Credit-
Based Authorization (CBA) approach is mandatory when a host sends
data to an UNVERIFIED locator. The following algorithm meets the
security considerations for prevention of amplification and time-
shifting attacks. Other forms of credit aging, and other values for
the CreditAgingFactor and CreditAgingInterval parameters in
particular, are for further study, and so are the advanced CBA
techniques specified in [10].
5.6.1. Handling Payload Packets
A host maintains a "credit counter" for each of its peers. Whenever A host maintains a "credit counter" for each of its peers. Whenever
a packet arrives from a peer, the host SHOULD increase that peer's a packet arrives from a peer, the host SHOULD increase that peer's
credit counter by the size of the received packet. When the host has credit counter by the size of the received packet. When the host has
a packet to be sent to the peer, if the peers preferred locator is a packet to be sent to the peer, and when the peer's Preferred
listed as UNVERIFIED and no alternative locator with status ACTIVE is locator is listed as UNVERIFIED and no alternative locator with
available, the host checks whether it can send the packet to the status ACTIVE is available, the host checks whether it can send the
UNVERIFIED locator: The packet SHOULD be sent if the value of the packet to the UNVERIFIED locator. The packet SHOULD be sent if the
credit counter is higher than the size of the outbound packet. If value of the credit counter is higher than the size of the outbound
the credit counter is too low, the packet MUST be discarded or packet. If the credit counter is too low, the packet MUST be
buffered until address verification succeeds. When a packet is sent discarded or buffered until address verification succeeds. When a
to a peer at an UNVERIFIED locator, the peer's credit counter MUST be packet is sent to a peer at an UNVERIFIED locator, the peer's credit
reduced by the size of the packet. The peer's credit counter is not counter MUST be reduced by the size of the packet. The peer's credit
affected by packets that the host sends to an ACTIVE locator of that counter is not affected by packets that the host sends to an ACTIVE
peer. locator of that peer.
Figure 15 depicts the actions taken by the host when a packet is Figure 14 depicts the actions taken by the host when a packet is
received. Figure 16 shows the decision chain in the event a packet received. Figure 15 shows the decision chain in the event a packet
is sent. is sent.
Inbound Inbound
packet packet
| |
| +----------------+ +---------------+ | +----------------+ +---------------+
| | Increase | | Deliver | | | Increase | | Deliver |
+-----> | credit counter |-------------> | packet to | +-----> | credit counter |-------------> | packet to |
| by packet size | | application | | by packet size | | application |
+----------------+ +---------------+ +----------------+ +---------------+
Figure 15: Receiving Packets with Credit-Based Authorization Figure 14: Receiving Packets with Credit-Based Authorization
Outbound Outbound
packet packet
| _________________ | _________________
| / \ +---------------+ | / \ +---------------+
| / Is the preferred \ No | Send packet | | / Is the preferred \ No | Send packet |
+-----> | destination address |-------------> | to preferred | +-----> | destination address |-------------> | to preferred |
\ UNVERIFIED? / | address | \ UNVERIFIED? / | address |
\_________________/ +---------------+ \_________________/ +---------------+
| |
| Yes | Yes
skipping to change at page 33, line 42 skipping to change at page 34, line 42
| |
| Yes | Yes
| |
v v
+---------------+ +---------------+ +---------------+ +---------------+
| Reduce credit | | Send packet | | Reduce credit | | Send packet |
| counter by |----------------> | to preferred | | counter by |----------------> | to preferred |
| packet size | | address | | packet size | | address |
+---------------+ +---------------+ +---------------+ +---------------+
Figure 16: Sending Packets with Credit-Based Authorization Figure 15: Sending Packets with Credit-Based Authorization
5.5.2. Credit Aging 5.6.2. Credit Aging
A host ensures that the credit counters it maintains for its peers A host ensures that the credit counters it maintains for its peers
gradually decrease over time. Such "credit aging" prevents a gradually decrease over time. Such "credit aging" prevents a
malicious peer from building up credit at a very slow speed and using malicious peer from building up credit at a very slow speed and using
this, all at once, for a severe burst of redirected packets. this, all at once, for a severe burst of redirected packets.
Credit aging may be implemented by multiplying credit counters with a Credit aging may be implemented by multiplying credit counters with a
factor, CreditAgingFactor, less than one in fixed time intervals of factor, CreditAgingFactor (a fractional value less than one), in
CreditAgingInterval length. Choosing appropriate values for fixed time intervals of CreditAgingInterval length. Choosing
CreditAgingFactor and CreditAgingInterval is important to ensure that appropriate values for CreditAgingFactor and CreditAgingInterval is
a host can send packets to an address in state UNVERIFIED even when important to ensure that a host can send packets to an address in
the peer sends at a lower rate than the host itself. When state UNVERIFIED even when the peer sends at a lower rate than the
CreditAgingFactor or CreditAgingInterval are too small, the peer's host itself. When CreditAgingFactor or CreditAgingInterval are too
credit counter might be too low to continue sending packets until small, the peer's credit counter might be too low to continue sending
address verification concludes. packets until address verification concludes.
The parameter values proposed in this document are as follows: The parameter values proposed in this document are as follows:
CreditAgingFactor 7/8 CreditAgingFactor 7/8
CreditAgingInterval 5 seconds CreditAgingInterval 5 seconds
These parameter values work well when the host transfers a file to These parameter values work well when the host transfers a file to
the peer via a TCP connection and the end-to-end round-trip time does the peer via a TCP connection and the end-to-end round-trip time does
not exceed 500 milliseconds. Alternative credit-aging algorithms may not exceed 500 milliseconds. Alternative credit-aging algorithms may
use other parameter values or different parameters, which may even be use other parameter values or different parameters, which may even be
dynamically established. dynamically established.
5.6. Changing the preferred locator
A host MAY want to change the preferred outgoing locator for
different reasons, e.g., because traffic information or ICMP error
messages indicate that the currently used preferred address may have
become unreachable. Another reason may be due to receiving a LOCATOR
parameter that has the P-bit set.
To change the preferred locator, the host initiates the following
procedure:
1. If the new preferred locator has ACTIVE status, the preferred
locator is changed and the procedure succeeds.
2. If the new preferred locator has UNVERIFIED status, the host
starts to verify its reachability. The host SHOULD use a
different locator listed as ACTIVE until address verification
completes if one such locator is available. Alternatively, the
host MAY use the new preferred locator, even though in UNVERIFIED
status, to the extent Credit-Based Authorization permits. Once
address verification succeeds, the status of the new preferred
locator changes to ACTIVE and its use is no longer governed by
Credit-Based Authorization.
3. If the peer host has not indicated a preference for any address,
then the host picks one of the peer's ACTIVE addresses randomly
or according to policy. This case may arise if, for example,
ICMP error messages arrive that deprecate the preferred locator,
but the peer has not yet indicated a new preferred locator.
4. If the new preferred locator has DEPRECATED status and there is
at least one non-deprecated address, the host selects one of the
non-deprecated addresses as a new preferred locator and
continues. If the selected address is UNVERIFIED, this includes
address verification as described above.
6. Security Considerations 6. Security Considerations
The HIP mobility mechanism provides a secure means of updating a The HIP mobility mechanism provides a secure means of updating a
host's IP address via HIP UPDATE packets. Upon receipt, a HIP host host's IP address via HIP UPDATE packets. Upon receipt, a HIP host
cryptographically verifies the sender of an UPDATE, so forging or cryptographically verifies the sender of an UPDATE, so forging or
replaying a HIP UPDATE packet is very difficult (see [2]). replaying a HIP UPDATE packet is very difficult (see [2]).
Therefore, security issues reside in other attack domains. The two Therefore, security issues reside in other attack domains. The two
we consider are malicious redirection of legitimate connections as we consider are malicious redirection of legitimate connections as
well as redirection-based flooding attacks using this protocol. This well as redirection-based flooding attacks using this protocol. This
can be broken down into the following: can be broken down into the following:
skipping to change at page 36, line 40 skipping to change at page 36, line 40
* tool 2: redirection-based flooding * tool 2: redirection-based flooding
- memory-exhaustion attacks - memory-exhaustion attacks
- computational exhaustion attacks - computational exhaustion attacks
We consider these in more detail in the following sections. We consider these in more detail in the following sections.
In Section 6.1 and Section 6.2, we assume that all users are using In Section 6.1 and Section 6.2, we assume that all users are using
HIP. In Section 6.3 we consider the security ramifications when we HIP. In Section 6.3 we consider the security ramifications when we
have both HIP and non-HIP users. have both HIP and non-HIP users. Security considerations for Credit-
Based Authorization are discussed in [11].
6.1. Impersonation attacks 6.1. Impersonation attacks
An attacker wishing to impersonate will try to mislead its victim An attacker wishing to impersonate will try to mislead its victim
into directly communicating with them, or carry out a man in the into directly communicating with them, or carry out a man in the
middle attack between the victim and the victim's desired middle attack between the victim and the victim's desired
communication peer. Without mobility support, both attack types are communication peer. Without mobility support, both attack types are
possible only if the attacker resides on the routing path between its possible only if the attacker resides on the routing path between its
victim and the victim's desired communication peer, or if the victim and the victim's desired communication peer, or if the
attacker tricks its victim into initiating the connection over an attacker tricks its victim into initiating the connection over an
incorrect routing path (e.g., by acting as a router or using spoofed incorrect routing path (e.g., by acting as a router or using spoofed
DNS entries). DNS entries).
The HIP extensions defined in this specification change the situation The HIP extensions defined in this specification change the situation
in that they introduce an ability to redirect a connection (like in that they introduce an ability to redirect a connection (like
IPv6), both before and after establishment. If no precautionary IPv6), both before and after establishment. If no precautionary
measures are taken, an attacker could misuse this feature to measures are taken, an attacker could misuse the redirection feature
impersonate a victim's peer from any arbitrary location. The to impersonate a victim's peer from any arbitrary location. The
authentication and authorization mechanisms of the HIP base exchange authentication and authorization mechanisms of the HIP base exchange
[2] and the signatures in the UPDATE message prevent this attack. [2] and the signatures in the UPDATE message prevent this attack.
Furthermore, ownership of a HIP association is securely linked to a Furthermore, ownership of a HIP association is securely linked to a
HIP HI/HIT. If an attacker somehow uses a bug in the implementation HIP HI/HIT. If an attacker somehow uses a bug in the implementation
or weakness in some protocol to redirect a HIP connection, the or weakness in some protocol to redirect a HIP connection, the
original owner can always reclaim their connection (they can always original owner can always reclaim their connection (they can always
prove ownership of the private key associated with their public HI). prove ownership of the private key associated with their public HI).
MitM attacks are always possible if the attacker is present during MitM attacks are always possible if the attacker is present during
the initial HIP base exchange and if the hosts do not authenticate the initial HIP base exchange and if the hosts do not authenticate
each other's identities, but once the base exchange has taken place each other's identities. However, once the opportunistic base
even a MitM cannot steal an opportunistic HIP connection because it exchange has taken place, even a MitM cannot steal the HIP connection
is very difficult for an attacker to create an UPDATE packet (or any anymore because it is very difficult for an attacker to create an
HIP packet) that will be accepted as a legitimate update. UPDATE UPDATE packet (or any HIP packet) that will be accepted as a
packets use HMAC and are signed. Even when an attacker can snoop legitimate update. UPDATE packets use HMAC and are signed. Even
packets to obtain the SPI and HIT/HI, they still cannot forge an when an attacker can snoop packets to obtain the SPI and HIT/HI, they
UPDATE packet without knowledge of the secret keys. still cannot forge an UPDATE packet without knowledge of the secret
keys.
6.2. Denial of Service attacks 6.2. Denial of Service attacks
6.2.1. Flooding Attacks 6.2.1. Flooding Attacks
The purpose of a denial-of-service attack is to exhaust some resource The purpose of a denial-of-service attack is to exhaust some resource
of the victim such that the victim ceases to operate correctly. A of the victim such that the victim ceases to operate correctly. A
denial-of-service attack can aim at the victim's network attachment denial-of-service attack can aim at the victim's network attachment
(flooding attack), its memory, or its processing capacity. In a (flooding attack), its memory, or its processing capacity. In a
flooding attack the attacker causes an excessive number of bogus or flooding attack the attacker causes an excessive number of bogus or
skipping to change at page 38, line 10 skipping to change at page 38, line 13
With the ability to redirect connections, an attacker could realize a With the ability to redirect connections, an attacker could realize a
DDoS attack without having to distribute viral code. Here, the DDoS attack without having to distribute viral code. Here, the
attacker initiates a large download from a server, and subsequently attacker initiates a large download from a server, and subsequently
redirects this download to its victim. The attacker can repeat this redirects this download to its victim. The attacker can repeat this
with multiple servers. This threat is mitigated through reachability with multiple servers. This threat is mitigated through reachability
checks and credit-based authorization. Both strategies do not checks and credit-based authorization. Both strategies do not
eliminate flooding attacks per se, but they preclude: (i) their use eliminate flooding attacks per se, but they preclude: (i) their use
from a location off the path towards the flooded victim; and (ii) any from a location off the path towards the flooded victim; and (ii) any
amplification in the number and size of the redirected packets. As a amplification in the number and size of the redirected packets. As a
result, the combination of a reachability check and credit-based result, the combination of a reachability check and credit-based
authorization makes a HIP redirection-based flooding attack as authorization lowers a HIP redirection-based flooding attack to the
effective and applicable as a normal, direct flooding attack in which level of a direct flooding attack in which the attacker itself sends
the attacker itself sends the flooding traffic to the victim. the flooding traffic to the victim.
This analysis leads to the following two points. First, when a
reachability packet is received, this nonce packet MUST be ignored if
the HIT is not one that is currently active. Second, if the attacker
is a MitM and can capture this nonce packet then it can respond to
it, in which case it is possible for an attacker to redirect the
connection. Note, this attack will always be possible when a
reachability packet is not sent.
6.2.2. Memory/Computational exhaustion DoS attacks 6.2.2. Memory/Computational exhaustion DoS attacks
We now consider whether or not the proposed extensions to HIP add any We now consider whether or not the proposed extensions to HIP add any
new DoS attacks (consideration of DoS attacks using the base HIP new DoS attacks (consideration of DoS attacks using the base HIP
exchange and updates is discussed in [2]). A simple attack is to exchange and updates is discussed in [2]). A simple attack is to
send many UPDATE packets containing many IP addresses that are not send many UPDATE packets containing many IP addresses that are not
flagged as preferred. The attacker continues to send such packets flagged as preferred. The attacker continues to send such packets
until the number of IP addresses associated with the attacker's HI until the number of IP addresses associated with the attacker's HI
crashes the system. Therefore, there SHOULD be a limit to the number crashes the system. Therefore, there SHOULD be a limit to the number
of IP addresses that can be associated with any HI. Other forms of of IP addresses that can be associated with any HI. Other forms of
memory/computationally exhausting attacks via the HIP UPDATE packet memory/computationally exhausting attacks via the HIP UPDATE packet
are handled in the base HIP draft [2]. are handled in the base HIP draft [2].
A central server that has to deal with a large number of mobile
clients may consider increasing the SA lifetimes to try to slow down
the rate of rekeying UPDATEs or increasing the cookie difficulty to
slow down the rate of attack-oriented connections.
6.3. Mixed deployment environment 6.3. Mixed deployment environment
We now assume an environment with both HIP and non-HIP aware hosts. We now assume an environment with both HIP and non-HIP aware hosts.
Four cases exist. Four cases exist.
1. A HIP user redirects their connection onto a non-HIP user. The 1. A HIP host redirects its connection onto a non-HIP host. The
non-HIP user will drop the reachability packet so this is not a non-HIP host will drop the reachability packet, so this is not a
threat unless the HIP user is a MitM and can respond to the threat unless the HIP host is a MitM that could somehow respond
reachability packet. successfully to the reachability check.
2. A non-HIP user attempts to redirect their connection onto a HIP 2. A non-HIP host attempts to redirect their connection onto a HIP
user. This falls into IPv4 and IPv6 security concerns, which are host. This falls into IPv4 and IPv6 security concerns, which are
outside the scope of this document. outside the scope of this document.
3. A non-HIP user attempts to steal a HIP user's session (assume 3. A non-HIP host attempts to steal a HIP host's session (assume
that Secure Neighbor Discovery is not active for the following). that Secure Neighbor Discovery is not active for the following).
The non-HIP user contacts the service that a HIP user has a The non-HIP host contacts the service that a HIP host has a
connection with and then attempts to use a IPv6 change of address connection with and then attempts to change its IP address to
request to steal the HIP user's connection. What will happen in steal the HIP host's connection. What will happen in this case
this case is implementation dependent but such a request should is implementation dependent but such a request should fail by
be ignored/dropped. Even if the attack is successful, the HIP being ignored or dropped. Even if the attack were successful,
user can reclaim its connection via HIP. the HIP host could reclaim its connection via HIP.
4. A HIP user attempts to steal a non-HIP user's session. This 4. A HIP host attempts to steal a non-HIP host's session. A HIP
could be problematic since HIP sits 'on top of' layer 3. A HIP host could spoof the non-HIP host's IP address during the base
user could spoof the non-HIP user's IP address during the base exchange or set the non-HIP host's IP address as its preferred
exchange or set the non-HIP user's IP address as their preferred
address via an UPDATE. Other possibilities exist but a simple address via an UPDATE. Other possibilities exist but a simple
solution is to add a check which does not allow any HIP session solution is to prevent use of HIP address check information to
to be moved to or created upon an already existing IP address. influence non-HIP sessions.
7. IANA Considerations 7. IANA Considerations
This document defines a LOCATOR parameter for the Host Identity This document defines a LOCATOR parameter for the Host Identity
Protocol [2]. This parameter is defined in Section 4 with a Type of Protocol [2]. This parameter is defined in Section 4 with a Type of
193. 193.
8. Authors 8. Authors and Acknowledgments
Pekka Nikander originated this Internet Draft. Tom Henderson, Jari Pekka Nikander originated this Internet Draft. Tom Henderson, Jari
Arkko, Greg Perkins, and Christian Vogt have each contributed Arkko, Greg Perkins, and Christian Vogt have each contributed
sections to this draft. sections to this draft.
9. Acknowledgments The authors thank Miika Komu, Mika Kousa, Jeff Ahrenholz, and Jan
Melen for many improvements to the draft.
The authors thank Mika Kousa, Jeff Ahrenholz, and Jan Melen for many
improvements to the draft.
10. References 9. References
10.1. Normative references 9.1. Normative references
[1] Moskowitz, R. and P. Nikander, "Host Identity Protocol [1] Moskowitz, R. and P. Nikander, "Host Identity Protocol
Architecture", draft-ietf-hip-arch-03 (work in progress), Architecture", RFC 4423, August 2005.
August 2005.
[2] Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-04 [2] Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-05
(work in progress), October 2005. (work in progress), March 2006.
[3] Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) [3] Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
Rendezvous Extension", draft-ietf-hip-rvs-04 (work in progress), Rendezvous Extension", draft-ietf-hip-rvs-04 (work in progress),
October 2005. October 2005.
[4] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, [4] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303,
December 2005. December 2005.
[5] Jokela, P., "Using ESP transport format with HIP", [5] Draves, R., "Default Address Selection for Internet Protocol
draft-ietf-hip-esp-01 (work in progress), October 2005. version 6 (IPv6)", RFC 3484, February 2003.
[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement [6] Jokela, P., "Using ESP transport format with HIP",
draft-ietf-hip-esp-02 (work in progress), March 2006.
[7] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[7] Hinden, R. and S. Deering, "IP Version 6 Addressing [8] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998. Architecture", RFC 2373, July 1998.
10.2. Informative references 9.2. Informative references
[8] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E. [9] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E.
Nordmark, "Mobile IP Version 6 Route Optimization Security Nordmark, "Mobile IP Version 6 Route Optimization Security
Design Background", RFC 4225, December 2005. Design Background", RFC 4225, December 2005.
[10] Vogt, C. and J. Arkko, "Credit-Based Authorization for Mobile
IPv6 Early Binding Updates",
draft-vogt-mobopts-credit-based-authorization-00 (work in
progress), February 2005.
[11] Vogt, C. and J. Arkko, "Credit-Based Authorization for
Concurrent Reachability Verification",
draft-vogt-mobopts-simple-cba-00 (work in progress),
February 2006.
Appendix A. Changes from previous versions Appendix A. Changes from previous versions
A.1. From nikander-hip-mm-00 to nikander-hip-mm-01 A.1. From nikander-hip-mm-00 to nikander-hip-mm-01
The actual protocol has been largely revised, based on the new The actual protocol has been largely revised, based on the new
symmetric New SPI (NES) design adopted in the base protocol draft symmetric New SPI (NES) design adopted in the base protocol draft
version -08. There are no more separate REA, AC or ACR packets, but version -08. There are no more separate REA, AC or ACR packets, but
their functionality has been folded into the NES packet. At the same their functionality has been folded into the NES packet. At the same
time, it has become possible to send REA parameters in R1 and I2. time, it has become possible to send REA parameters in R1 and I2.
skipping to change at page 47, line 5 skipping to change at page 45, line 34
in separate UPDATE because R2 is not an acknowledged packet) in separate UPDATE because R2 is not an acknowledged packet)
Removed first four paragraphs of Section 5, which were redundant with Removed first four paragraphs of Section 5, which were redundant with
previous introductory material. previous introductory material.
Rewrote Sections 5.2 and 5.3 on sending and receiving LOCATOR, to Rewrote Sections 5.2 and 5.3 on sending and receiving LOCATOR, to
more explicitly cover the scenario scope of this document. more explicitly cover the scenario scope of this document.
Removed unwritten "Policy Considerations" section Removed unwritten "Policy Considerations" section
A.7. From draft-ietf-hip-mm-03 to -04
Responded to numerous WGLC comments and corrections from Miika Komu
(responses on the HIP mailing list)
Author's Address Author's Address
Tom Henderson Tom Henderson
The Boeing Company The Boeing Company
P.O. Box 3707 P.O. Box 3707
Seattle, WA Seattle, WA
USA USA
Email: thomas.r.henderson@boeing.com Email: thomas.r.henderson@boeing.com
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