draft-ietf-hip-mm-00.txt   draft-ietf-hip-mm-01.txt 
Network Working Group P. Nikander Network Working Group P. Nikander
Internet-Draft J. Arkko Internet-Draft J. Arkko
Expires: April 17, 2005 Ericsson Research Nomadic Lab Expires: August 21, 2005 Ericsson Research Nomadic Lab
T. Henderson T. Henderson
The Boeing Company The Boeing Company
October 17, 2004 February 20, 2005
End-Host Mobility and Multi-Homing with Host Identity Protocol End-Host Mobility and Multi-Homing with the Host Identity Protocol
draft-ietf-hip-mm-00 draft-ietf-hip-mm-01
Status of this Memo Status of this Memo
This document is an Internet-Draft and is subject to all provisions This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. By submitting this Internet-Draft, each of section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of author represents that any applicable patent or other IPR claims of
which he or she is aware have been or will be disclosed, and any of which he or she is aware have been or will be disclosed, and any of
which he or she become aware will be disclosed, in accordance with which he or she become aware will be disclosed, in accordance with
RFC 3668. RFC 3668.
skipping to change at page 1, line 38 skipping to change at page 1, line 38
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on April 17, 2005. This Internet-Draft will expire on August 21, 2005.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). Copyright (C) The Internet Society (2005).
Abstract Abstract
This document specifies basic end-host mobility and multi-homing This document defines a "locator" parameter for the Host Identity
mechanisms for the Host Identity Protocol. Protocol and specifies an end-host mobility mechanism.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction and Scope . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 5 2. Conventions used in this document . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Overview of HIP basic mobility and multi-homing 4. LOCATOR parameter format . . . . . . . . . . . . . . . . . . . 7
functionality . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1 Traffic Type and Preferred Locator . . . . . . . . . . . . 8
4.1 Informing the peer about multiple or changed 4.2 Locator Type and Locator . . . . . . . . . . . . . . . . . 8
address(es) . . . . . . . . . . . . . . . . . . . . . . . 7 4.3 UPDATE packet with included LOCATOR . . . . . . . . . . . 9
4.2 Address verification . . . . . . . . . . . . . . . . . . . 9 5. Overview of HIP basic mobility and multi-homing
4.3 Preferred address . . . . . . . . . . . . . . . . . . . . 10 functionality . . . . . . . . . . . . . . . . . . . . . . . . 10
4.4 Address data structure and status . . . . . . . . . . . . 11 5.1 Informing the peer about multiple or changed locator(s) . 10
5. Protocol overview . . . . . . . . . . . . . . . . . . . . . . 12 5.2 Address verification . . . . . . . . . . . . . . . . . . . 13
5.1 Mobility with single SA pair . . . . . . . . . . . . . . . 12 5.3 Preferred locator . . . . . . . . . . . . . . . . . . . . 13
5.2 Host multihoming . . . . . . . . . . . . . . . . . . . . . 14 5.4 Locator data structure and status . . . . . . . . . . . . 14
5.3 Site multi-homing . . . . . . . . . . . . . . . . . . . . 16 6. Protocol overview . . . . . . . . . . . . . . . . . . . . . . 15
5.4 Dual host multi-homing . . . . . . . . . . . . . . . . . . 16 6.1 Mobility with single SA pair . . . . . . . . . . . . . . . 15
5.5 Combined mobility and multi-homing . . . . . . . . . . . . 17 6.2 Host multihoming . . . . . . . . . . . . . . . . . . . . . 17
5.6 Network renumbering . . . . . . . . . . . . . . . . . . . 17 6.3 Site multi-homing . . . . . . . . . . . . . . . . . . . . 19
5.7 Initiating the protocol in R1 or I2 . . . . . . . . . . . 17 6.4 Dual host multi-homing . . . . . . . . . . . . . . . . . . 19
6. Parameter and packet formats . . . . . . . . . . . . . . . . . 19 6.5 Combined mobility and multi-homing . . . . . . . . . . . . 20
6.1 REA parameter . . . . . . . . . . . . . . . . . . . . . . 19 6.6 Using LOCATORs across addressing realms . . . . . . . . . 20
6.2 UPDATE packet with included REA . . . . . . . . . . . . . 20 6.7 Network renumbering . . . . . . . . . . . . . . . . . . . 20
7. Processing rules . . . . . . . . . . . . . . . . . . . . . . . 21 6.8 Initiating the protocol in R1 or I2 . . . . . . . . . . . 20
7.1 Sending REAs . . . . . . . . . . . . . . . . . . . . . . . 21 7. Processing rules . . . . . . . . . . . . . . . . . . . . . . . 22
7.2 Handling received REAs . . . . . . . . . . . . . . . . . . 22 7.1 Sending LOCATORs . . . . . . . . . . . . . . . . . . . . . 22
7.3 Verifying address reachability . . . . . . . . . . . . . . 23 7.2 Handling received LOCATORs . . . . . . . . . . . . . . . . 23
7.4 Changing the preferred address . . . . . . . . . . . . . . 24 7.3 Verifying address reachability . . . . . . . . . . . . . . 24
8. Policy considerations . . . . . . . . . . . . . . . . . . . . 25 7.4 Changing the preferred locator . . . . . . . . . . . . . . 24
9. Security Considerations . . . . . . . . . . . . . . . . . . . 26 8. Policy considerations . . . . . . . . . . . . . . . . . . . . 26
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 27 9. Security Considerations . . . . . . . . . . . . . . . . . . . 27
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 28 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 28
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 29 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 29
12.1 Normative references . . . . . . . . . . . . . . . . . . . . 29 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
12.2 Informative references . . . . . . . . . . . . . . . . . . . 29 12.1 Normative references . . . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 29 12.2 Informative references . . . . . . . . . . . . . . . . . . . 30
A. Changes from previous versions . . . . . . . . . . . . . . . . 31 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 30
A.1 From nikander-hip-mm-00 to nikander-hip-mm-01 . . . . . . 31 A. Changes from previous versions . . . . . . . . . . . . . . . . 32
A.2 From nikander-hip-mm-01 to nikander-hip-mm-02 . . . . . . 31 A.1 From nikander-hip-mm-00 to nikander-hip-mm-01 . . . . . . 32
A.3 From -02 to draft-ietf-hip-mm-00 . . . . . . . . . . . . . 31 A.2 From nikander-hip-mm-01 to nikander-hip-mm-02 . . . . . . 32
B. Implementation experiences . . . . . . . . . . . . . . . . . . 33 A.3 From -02 to draft-ietf-hip-mm-00 . . . . . . . . . . . . . 32
A.4 From draft-ietf-hip-mm-00 to -01 . . . . . . . . . . . . . 33
Intellectual Property and Copyright Statements . . . . . . . . 34 Intellectual Property and Copyright Statements . . . . . . . . 34
1. Introduction 1. Introduction and Scope
This document specifies an extension to the Host Identity Protocol
[3] (HIP). The extension provides a means for hosts to keep their
communications on-going while having multiple IP addresses, either at
the same time or one after another. That is, the extension provides
basic end-to-end support for multi-homing, mobility, and simultaneous
multi-homing and mobility. Additionally, the extension allows
communications to continue even when multi-homing or mobility causes
a change of the IP version that is available in the network; that is,
if one of the communicating hosts has both IPv4 and IPv6
connectivity, either directly or through a proxy, the other host can
alternate between IPv4 and IPv6, without needing to tear down and
re-establish upper layer protocol connections or associations. In
other words, the way upper layer protocols need to react to
cross-IP-version handovers does not differ from the way they need to
react to intra-IP-version handovers.
This document does not specify any rendezvous or proxy services.
Those are subject to other specifications. Hence, this document
alone does not necessarily allow two mobile hosts to communicate,
unless they have other means for initial rendezvous and for solving
the simultaneous movement problem.
The Host Identity Protocol [3] (HIP) defines a mechanism that The Host Identity Protocol [1] (HIP) defines a mechanism that
decouples the transport layer (TCP, UDP, etc) from the decouples the transport layer (TCP, UDP, etc) from the
internetworking layer (IPv4 and IPv6), and introduces a new Host internetworking layer (IPv4 and IPv6). When a host uses HIP, the
Identity namespace. When a host uses HIP, the transport layer overlying protocol sublayers (e.g., transport layer sockets and ESP
sockets and IPsec Security Associations are not bound to IP addresses Security Associations) are not bound to IP addresses but instead to
but to Host Identifiers. This document specifies how the mapping Host Identifiers. However, the hosts must also know at least one IP
from Host Identifiers to IP addresses can be extended from a static address where their peers are reachable. Initially these IP
one-to-one mapping into a dynamic one-to-many mapping, thereby addresses are the ones used during the HIP base exchange.
enabling end-host mobility and multi-homing.
In practice, the HIP base exchange [3] creates a pair of IPsec This document defines a generalization of an address called a
Security Associations (SA) between a pair of HIP enabled hosts. "locator". A locator specifies a point-of-attachment to the network
These SAs are not bound to IP addresses, but to the Host Identifiers but may also include additional end-to-end tunneling or per-host
(public keys) used to create them. However, the hosts must also know demultiplexing context that affects how packets are handled below the
at least one IP address where their peers are reachable. Initially logical HIP sublayer. This generalization is useful because IP
these IP addresses are the ones used during the HIP base exchange. addresses alone may not be sufficient to describe how packets should
be handled below HIP. For example, in a host multihoming context,
certain IP addresses may need to be associated with certain ESP SPIs,
to avoid violation of the ESP anti-replay window [2]. Addresses may
also be affiliated with transport ports in certain tunneling
scenarios. Or locators may merely be traditional network addresses.
Since the SAs are not bound to IP addresses, the host is able to Using the locator concept, this document specifies extensions to HIP
receive packets that are protected using a HIP created ESP SA from to allow a mobile host to directly inform a correspondent host, with
any address. Thus, a host can change its IP address and continue to whom the host has an active HIP association, of a locator change.
send packets to its peers. However, unless the host is sufficiently The extensions consist of a new LOCATOR parameter for use in HIP
trusted, the peers are not able to reply before they can reliably and messages, packet processing procedures for using HIP messages to
securely update the set of addresses that they associate with the securely notify the peer of a locator change, and additional
sending host. Furthermore, mobility may change the path procedures such as an address check mechanism.
characteristics in such a manner that reordering occurs and packets
fall outside the ESP anti-replay window.
This document specifies a mechanism that allows a HIP host to update When using ESP, since the SAs are not bound to IP addresses, the host
the set of addresses that its peers associate with it. The address is able to receive packets that are protected using a HIP created ESP
update is implemented with new HIP parameter types. Due to the SA from any address. Thus, a host can change its IP address and
danger of flooding attacks (see [4]), the peers must always check the continue to send packets to its peers. However, unless the host is
reachability of the host at a new address, unless sufficient level of sufficiently trusted by its peers, the peers are not able to reply
trust exists between the hosts. before they can reliably and securely update the set of addresses
that they associate with the sending host. Furthermore, mobility may
change the path characteristics in such a manner that reordering
occurs and packets fall outside the ESP anti-replay window.
The reachability check is implemented by the challenger sending some A related operational configuration is host multihoming, in which a
host has multiple locators simultaneously rather than sequentially as
in the case of mobility. By using the locator parameter defined
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
"preferred" locator. Although this document defines a mechanism for
multihoming, it does not define associated policies such as which
locators to choose when more than one pair is available, the
operation of simultaneous mobility and multihoming, and the
implications of multihoming on transport protocols and ESP
anti-replay windows. Additional definition of HIP-based multihoming
is expected to be part of a future document.
Due to the danger of flooding attacks (see [3]), the peers must
always check the reachability of the host at a new IP address, unless
a sufficient level of trust exists between the hosts. The
reachability check 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.
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, end-host and initial reachability of a mobile host, location privacy, end-host and
site multi-homing with legacy hosts, and NAT traversal. In these site multi-homing with legacy hosts, and 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. This document does not address those needs. network. Such functionality is out of scope of this document.
Finally, making underlying IP mobility transparent to the transport Finally, making underlying IP mobility transparent to the transport
layer has implications on the proper response of transport congestion layer has implications on the proper response of transport congestion
control, path MTU selection, and QoS. Transport-layer mobility control, path MTU selection, and QoS. Transport-layer mobility
triggers, and the proper transport response to a HIP mobility or triggers, and the proper transport response to a HIP mobility or
multi-homing address change, are outside the scope of this document. multi-homing address change, are outside the scope of this document.
2. Conventions used in this document 2. Conventions used in this document
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 [1]. document are to be interpreted as described in RFC2119 [4].
3. Terminology 3. Terminology
Preferred address An address on which a host prefers to receive data. Locator. A name that controls how the packet is routed through the
With respect to a given peer, a host always has one active network and demultiplexed by the end host. It may include a
preferred address. By default, the source address used in the HIP concatenation of traditional network addresses such as an IPv6
base exchange is the preferred address. address and end-to-end identifiers such as an ESP SPI. It may
New preferred address A new preferred address sent by a host to its also include transport port numbers or IPv6 Flow Labels as
peers. The reachability of the new preferred address often needs demultiplexing context, or it may simply be a network address.
to be verified before it can be taken into use. Consequently, Address. A name that denotes a point-of-attachment to the network.
there may simultaneously be an active preferred address, being The two most common examples are an IPv4 address and an IPv6
used, and a new preferred address, the reachability of which is address. The set of possible addresses is a subset of the set of
being verified. possible locators.
Preferred locator. A locator on which a host prefers to receive
data. With respect to a given peer, a host always has one active
preferred locator, unless there are no active locators. By
default, the locators used in the HIP base exchange are the
preferred locators.
New preferred locator. A new preferred locator sent by a host to its
peers. The reachability of the new preferred locator often needs
to be verified before it can be put into use. Consequently, there
may simultaneously be an active preferred locator, being used, and
a new preferred locator, the reachability of which is being
verified.
4. Overview of HIP basic mobility and multi-homing functionality 4. LOCATOR parameter format
The LOCATOR parameter is a critical parameter as defined by [1]. The
LOCATOR parameter is also abbreviated as "LOC" in the figures herein.
It consists of the standard HIP parameter Type and Length fields,
plus one or more locator sub-parameters. Each Locator sub-parameter
contains a Traffic Type, Locator Type, Locator Length, Preferred
Locator bit, Locator Lifetime, and a Locator encoding.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Type | Locator Type | Locator Length | Reserved |P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Locator Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Locator |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Type | Locator Type | Locator Length | Reserved |P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Locator Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Locator |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 3
Length: Length in octets, excluding Type and Length fields, and
excluding padding.
Traffic Type: Defines whether the locator pertains to HIP signaling,
user data, or both.
Locator Type: Defines the semantics of the Locator field.
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
supported).
Reserved: Zero when sent, ignored when received.
P: Preferred locator. Set to one if the locator is preferred for
that Traffic Type; otherwise set to zero.
Locator Lifetime: Locator lifetime, in seconds.
Locator: The locator whose semantics and encoding are indicated by
the Locator Type field. All Locator sub-fields are integral
multiples of four bytes in length.
The Locator Lifetime indicates how long the following locator is
expected to be valid. The lifetime is expressed in seconds. Each
locator MUST have a non-zero lifetime. The address is expected to
become deprecated when the specified number of seconds has passed
since the reception of the message. A deprecated address SHOULD NOT
be used as an destination address if an alternate (non-deprecated) is
available and has sufficient scope.
4.1 Traffic Type and Preferred Locator
The following Traffic Type values are defined:
0: Both signaling (HIP control packets) and user data.
1: Signaling packets only.
2: Data packets only.
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",
for example, that means that the locator is preferred for data
packets. If there is a conflict (for example, if P bit is set for
both "0" and "2"), the more specific Traffic Type rule applies. By
default, the IP addresses used in the base exchange are preferred
locators for both signaling and user data, unless a new preferred
locator supersedes them. If no locators are indicated as preferred
for a given Traffic Type, the implementation may use an arbitrary
locator from the set of active locators.
4.2 Locator Type and Locator
The following Locator Type values are defined, along with the
associated semantics of the Locator field:
0: An IPv6 address or an IPv4-in-IPv6 format IPv4 address [5] (128
bits long).
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
128 bits).
4.3 UPDATE packet with included LOCATOR
A number of combinations of parameters in an UPDATE packet are
possible (e.g., see Section 6). Any UPDATE packet that includes a
LOCATOR parameter SHOULD include both an HMAC and a HIP_SIGNATURE
parameter.>
5. Overview of HIP basic mobility and multi-homing functionality
HIP mobility and multi-homing is fundamentally based on the HIP HIP mobility and multi-homing is fundamentally based on the HIP
architecture [4], where the transport and internetworking layers are architecture [3], where the transport and internetworking layers are
decoupled from each other by an interposed host identity protocol decoupled from each other by an interposed host identity protocol
layer. In the HIP architecture, the transport layer sockets are layer. In the HIP architecture, the transport layer sockets are
bound to the Host Identifiers (through HIT or LSI in the case of bound to the Host Identifiers (through HIT or LSI in the case of
legacy APIs), and the Host Identifiers are translated to the actual legacy APIs), and the Host Identifiers are translated to the actual
IP address. IP address.
The HIP base protocol specification [3] defines how two hosts The HIP base protocol specification [1] is expected to be commonly
exchange their Host Identifiers and establish a pair of ESP Security used with the ESP Transport Format [6] to establish a pair of
Associations (SA). The ESP SAs are then used to carry the actual Security Associations (SA). The ESP SAs are then used to carry the
payload data between the two hosts, by wrapping TCP, UDP, and other actual payload data between the two hosts, by wrapping TCP, UDP, and
upper layer packets into transport mode ESP payloads. The IP header other upper layer packets into transport mode ESP payloads. The IP
uses the actual IP addresses in the network. header uses the actual IP addresses in the network.
Although HIP may also be specified in the future to operate with an
alternative to ESP providing the per-packet HIP context, the
remainder of this document assumes that HIP is being used in
conjunction with ESP. Future documents may extend this document to
include other behaviors when ESP is not used.
The base specification does not contain any mechanisms for changing The base specification does not contain any mechanisms for changing
the IP addresses that were used during the base HIP exchange. Hence, the IP addresses that were used during the base HIP exchange. Hence,
in order to remain connected, any systems that implement only the in order to remain connected, any systems that implement only the
base specification and nothing else must retain the ability to base specification and nothing else must retain the ability to
receive packets at their primary IP address; that is, those systems receive packets at their primary IP address; that is, those systems
cannot change the IP address on which they are using to receive cannot change the IP address on which they are using to receive
packets without causing loss of connectivity until a base exchange is packets without causing loss of connectivity until a base exchange is
performed from the new address. performed from the new address.
4.1 Informing the peer about multiple or changed address(es) 5.1 Informing the peer about multiple or changed locator(s)
This document specifies a new HIP protocol parameter, the REA This document specifies a new HIP protocol parameter, the LOCATOR
parameter (see Section 6.1), that allows the hosts to exchange parameter (see Section 4), that allows the hosts to exchange
information about their IP address(es), and any changes in their information about their locator(s), and any changes in their
address(es). The logical structure created with REA parameters has locator(s). The logical structure created with LOCATOR parameters
three levels: hosts, IPsec 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 entities for an association negotiated as
defined in the base specification [3] is illustrated in Figure 1. defined in the base specification [1] and ESP transform [6] is
illustrated in Figure 2.
-<- SPI1a -- -- SPI2a ->- -<- SPI1a -- -- SPI2a ->-
host1 < > addr1a <---> addr2a < > host2 host1 < > addr1a <---> addr2a < > host2
->- SPI2a -- -- SPI1a -<- ->- SPI2a -- -- SPI1a -<-
Figure 1: Relation between hosts, SPIs, and addresses (base Figure 2: Relation between hosts, SPIs, and addresses (base
specification) specification)
In Figure 1, host1 and host2 negotiate two unidirectional IPsec SAs, In Figure 2, host1 and host2 negotiate two unidirectional SAs, and
and each host selects the SPI value for its inbound SA. The each host selects the SPI value for its inbound SA. The addresses
addresses addr1a and addr2a are the source addresses that each host addr1a and addr2a are the source addresses that each host uses in the
uses in the base HIP exchange. These are the "preferred" (and only) base HIP exchange. These are the "preferred" (and only) addresses
addresses conveyed to the peer for each SA; even though packets sent conveyed to the peer for each SA; even though packets sent to any of
to any of the hosts' interfaces can arrive on an inbound SPI, when a the hosts' interfaces can arrive on an inbound SPI, when a host sends
host sends packets to the peer on an outbound SPI, it knows of a packets to the peer on an outbound SPI, it knows of a single
single destination address associated with that outbound SPI (for destination address associated with that outbound SPI (for host1, it
host1, it sends a packet on SPI2a to addr2a to reach host2), unless sends a packet on SPI2a to addr2a to reach host2), unless other
other mechanisms exist to learn of new addresses. mechanisms 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 2. In corresponding to this draft can be depicted as shown in Figure 3. In
this figure, a host can have multiple inbound SPIs (and, not shown, this figure, a host can have multiple inbound SPIs (and, not shown,
multiple outbound SPIs) between itself and another host. multiple outbound SPIs) between itself and 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 IPsec selectors. These addresses bound to an SPI are not used as SA selectors.
Rather, the addresses are those addresses that are provided to the Rather, the addresses are those addresses that are provided to the
peer host, as hints for which addresses to use to reach the host on peer host, as hints for which addresses to use to reach the host on
that SPI. The REA parameter is used to change the set of addresses that SPI. The LOCATOR parameter allows for IP addresses and SPIs to
that a peer associates with a particular SPI. be combined to form generalized locators. The LOCATOR parameter is
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 2: Relation between hosts, SPIs, and addresses (general case) Figure 3: 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 is to group
the addresses into collections that are likely to experience fate the addresses into collections that are likely to experience fate
sharing. For example, if the host needs to change its addresses on sharing. For example, if the host needs to change its addresses on
SPI2, it is likely that both address21 and address22 will 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 multi-homing, one of the addresses may especially in the case of site multi-homing, 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 2, it may seem used as a selector for the SA. Therefore, in Figure 3, 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 IPsec ESP anti-replay window. For this reason, HIP outside of the ESP anti-replay window. For this reason, HIP provides
provides a mechanism to affiliate destination addresses with inbound a mechanism to affiliate destination addresses with inbound SPIs, if
SPIs, if there is a concern that replay windows might be violated 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 otherwise. In this sense, we can say that a given inbound SPI has an
"affinity" for certain inbound IP addresses, and this affinity is "affinity" for certain inbound IP addresses, and this affinity is
communicated to the peer host. Each physical interface SHOULD have a communicated to the peer host. Each physical interface SHOULD have a
separate SA, unless the ESP reordering window is loose. separate SA, unless the ESP anti-replay window is loose.
Moreover, even if the destination addresses used for a particular SPI Moreover, even if the destination addresses used for a particular SPI
are held constant, the use of different source addresses may also are held constant, the use of different source interfaces may also
cause packets to fall outside of the ESP replay window, since the cause packets to fall outside of the ESP anti-replay window, since
path traversed is often affected by the source address or interface the path traversed is often affected by the source address or
used. A host has no way to influence the source address on which a interface used. A host has no way to influence the source interface
peer uses to send its packets on a given SPI. Hosts SHOULD on which a peer uses to send its packets on a given SPI. Hosts
consistently use the same source address when sending to a particular SHOULD consistently use the same source interface when sending to a
destination IP address and SPI. For this reason, a host may find it particular destination IP address and SPI. For this reason, a host
useful to change its SPI or at least reset its ESP replay window when may find it useful to change its SPI or at least reset its ESP
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 IPsec ambiguity since the receiver will ignore the IP addresses as SA
selectors anyway. selectors anyway.
A single REA parameter contains data only about one SPI. To A single LOCATOR parameter contains data only about one SPI. To
simultaneously signal changes on several SPIs, it is necessary to simultaneously signal changes on several SPIs, it is necessary to
send several REA parameters. The packet structure supports this. send several LOCATOR parameters. The packet structure supports this.
If the REA parameter is sent in an UPDATE packet, then the receiver If the LOCATOR parameter is sent in an UPDATE packet, then the
will respond with an UPDATE acknowledgment. If the REA parameter is receiver will respond with an UPDATE acknowledgment. If the LOCATOR
sent in a NOTIFY, I2, or R2 packet, then the recipient may consider parameter is sent in a NOTIFY, I2, or R2 packet, then the recipient
the REA as informational, and act only when it needs to activate a may consider the LOCATOR as informational, and act only when it needs
new address. The use of REA in a NOTIFY message may not be to activate a new address. The use of LOCATOR in a NOTIFY message
compatible with middleboxes. may not be compatible with middleboxes.
4.2 Address verification 5.2 Address verification
When a HIP host receives a set of IP addresses from another HIP host When a HIP host receives a set of locators from another HIP host in a
in a REA, 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 a bogus addresses in order to peer host may be intentionally giving bogus addresses in order to
cause a packet flood towards the given address [7]. Thus, before the cause a packet flood towards the given addresses [9]. Thus, before
HIP host can actually use a new address, it must first check that the the HIP host can actually use a new address, it must first check that
peer is reachable at the new address. the peer is reachable at the new address.
A second benefit of performing an address check is to allow any A second benefit of performing an address check is to allow any
possible middleboxes in the network along the new path to obtain the possible middleboxes in the network along the new path to obtain the
peer host's inbound SPI. peer host's inbound SPI.
A simple technique to verify addresses is to send an UPDATE to the A simple technique to verify addresses is to send an UPDATE to the
host at the new address. The UPDATE packet SHOULD include a nonce, host at the new address. The UPDATE packet SHOULD include a nonce,
unguessable by anyone not on the path to the new address, that forces unguessable by anyone not on the path to the new address, that forces
the host to reply in a manner that confirms reception of the nonce. the host to reply in a manner that confirms reception of the nonce.
One direct way to perform this is to include an ECHO_REQUEST One direct way to perform this is to include an ECHO_REQUEST
skipping to change at page 10, line 35 skipping to change at page 13, line 47
It is not specified how a host knows whether or not middleboxes might It is not specified how a host knows whether or not middleboxes might
lie on its path, so a conservative assumption may be to always lie on its path, so a conservative assumption may be to always
include the SPI parameter. include the SPI parameter.
In certain networking scenarios, hosts may be trusted enough to In certain networking scenarios, hosts may be trusted enough to
bypass performing address verification. In such a case, the host MAY bypass performing address verification. In such a case, the host MAY
bypass the address verification step and put the addresses into bypass the address verification step and put the addresses into
immediate service. Note that this may not be compatible with immediate service. Note that this may not be compatible with
middlebox traversal. middlebox traversal.
4.3 Preferred address 5.3 Preferred locator
When a host has multiple addresses and SPIs, the peer host must When a host has multiple locators, the peer host must decide upon
decide upon which to use as a destination address. It may be that a which to use for outbound packets. It may be that a host would
host would prefer to receive data on a particular inbound interface. prefer to receive data on a particular inbound interface. HIP allows
HIP allows a particular address to be designated as a preferred a particular locator to be designated as a preferred locator, and
address, and communicated to the peer. communicated to the peer (see Section 4).
In general, when multiple addresses are used for a session, there is In general, when multiple locators are used for a session, there is
the question of using multiple addresses 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 addresses 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 an address. other means to detect the failure of a locator.
4.4 Address data structure and status 5.4 Locator data structure and status
In a typical implementation, each outgoing address is represented as In a typical implementation, each outgoing locator is represented as
a piece of state that contains the following data: a piece of state that contains the following data:
the actual bit pattern representing the IPv4 or IPv6 address, the actual bit pattern representing the locator,
lifetime (seconds), lifetime (seconds),
status (UNVERIFIED, ACTIVE, DEPRECATED). status (UNVERIFIED, ACTIVE, DEPRECATED).
The status is used to track the reachability of the address: The status is used to track the reachability of the address embedded
within the LOCATOR parameter:
UNVERIFIED indicates that the reachability of the address has not UNVERIFIED indicates that the reachability of the address has not
been verified yet, been verified yet,
ACTIVE indicates that the reachability of the address has been ACTIVE indicates that the reachability of the address has been
verified and the address has not been deprecated, verified and the address has not been deprecated,
DEPRECATED indicates that the address lifetime has expired DEPRECATED indicates that the locator lifetime has expired
The following state changes are allowed: The following state changes are allowed:
UNVERIFIED to ACTIVE The reachability procedure completes UNVERIFIED to ACTIVE The reachability procedure completes
successfully. successfully.
UNVERIFIED to DEPRECATED The address lifetime expires while it is UNVERIFIED to DEPRECATED The locator lifetime expires while it is
UNVERIFIED. UNVERIFIED.
ACTIVE to DEPRECATED The address lifetime expires while it is ACTIVE. ACTIVE to DEPRECATED The locator lifetime expires while it is ACTIVE.
ACTIVE to UNVERIFIED There has been no traffic on the address for ACTIVE to UNVERIFIED There has been no traffic on the address for
some time, and the local policy mandates that the address some time, and the local policy mandates that the address
reachability must be verified again before starting to use it reachability must be verified again before starting to use it
again. again.
DEPRECATED to UNVERIFIED The host receives a new lifetime for the DEPRECATED to UNVERIFIED The host receives a new lifetime for the
address. locator.
If a host is verifying reachability with another host, a DEPRECATED If a host is verifying reachability with another host, a DEPRECATED
address MUST NOT be changed to ACTIVE without first verifying its address MUST NOT be changed to ACTIVE without first verifying its
reachability. If reachability is not being verified, then the reachability. If reachability is not being verified, then the
UNVERIFIED state is a transient state that transitions immediately to UNVERIFIED state is a transient state that transitions immediately to
ACTIVE. ACTIVE.
5. Protocol overview 6. Protocol overview
In this section we briefly introduce a number of usage scenarios In this section we briefly introduce a number of usage scenarios
where the HIP mobility and multi-homing facility is useful. To where the HIP mobility and multi-homing facility is useful. These
understand these usage scenarios, the reader should be at least scenarios assume that HIP is being used with the ESP Transform,
minimally familiar with the HIP protocol specification [3]. However, although other scenarios may be defined in the future. To understand
for the (relatively) uninitiated reader it is most important to keep these usage scenarios, the reader should be at least minimally
in mind that in HIP the actual payload traffic is protected with ESP, familiar with the HIP protocol specification [1]. However, for the
and that the ESP SPI acts as an index to the right host-to-host (relatively) uninitiated reader it is most important to keep in mind
context. that in HIP the actual payload traffic is protected with ESP, and
that the ESP SPI acts as an index to the right host-to-host context.
Each of the scenarios below assumes that the HIP base exchange has Each of the scenarios below assumes that the HIP base exchange has
completed, and the hosts each have a single outbound SA to the peer completed, and the hosts each have a single outbound SA to the peer
host. Associated with this outbound SA is a single destination host. Associated with this outbound SA is a single destination
address of the peer host-- the source address used by the peer during address of the peer host-- the source address used by the peer during
the base exchange. the base exchange.
The readdressing protocol is an asymmetric protocol where one host, The readdressing protocol is an asymmetric protocol where one host,
called the mobile host, informs another host, called the peer host, called the mobile host, informs another host, called the peer host,
about changes of IP addresses on affected SPIs. The readdressing about changes of IP addresses on affected SPIs. The readdressing
exchange is designed to be piggybacked on a number of existing HIP exchange is designed to be piggybacked on a number of existing HIP
exchanges. The main packets on which the REA parameters are expected exchanges. The main packets on which the LOCATOR parameters are
to be carried on are UPDATE packets. However, some implementations expected to be carried on are UPDATE packets. However, some
may want to experiment with sending REA parameters also on other implementations may want to experiment with sending LOCATOR
packets, such as R1, I2, and NOTIFY. parameters also on other packets, such as R1, I2, and NOTIFY.
5.1 Mobility with single SA pair 6.1 Mobility with single SA pair
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
change in the advertised IPv6 prefixes on the link, a reconnected PPP change in the advertised IPv6 prefixes on the link, a reconnected PPP
link, a new DHCP lease, or an actual movement to another subnet. In link, a new DHCP lease, or an actual movement to another subnet. In
order to maintain its communication context, the host must inform its order to maintain its communication context, the host must inform its
peers about the new IP address. This first example considers the peers about the new IP address. This first example considers the
case in which the mobile host has only one interface, IP address, and case in which the mobile host has only one interface, IP address, and
a single pair of SAs (one inbound, one outbound). a single pair of SAs (one inbound, one outbound).
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 REA Upon obtaining a new IP address, the mobile host sends a LOCATOR
parameter to the peer host in an UPDATE message. The REA parameter to the peer host in an UPDATE message. The LOCATOR
indicates the following: the new IP address, the SPI associated indicates the new IP address and the SPI associated with the new
with the new IP address, the address lifetime, and whether the IP address by using a Locator Type of "1", the locator lifetime,
new address is a preferred address. The mobile host may and whether the new locator is a preferred locator. The mobile
optionally send a NES to create a new inbound SA, in which case host may optionally send a NES to create a new inbound SA, in
it transitions to state REKEYING. In this case, the REA contains which case it transitions to state REKEYING. In this case, the
the new SPI to use. Otherwise, the existing SPI is identified in Locator contains the new SPI to use. Otherwise, the existing SPI
the REA parameter, and the host waits for its UPDATE to be is identified in the Locator parameter, and the host waits for
acknowledged. its UPDATE to be acknowledged.
2. Depending on whether the mobile host initiated a rekey, and on 2. Depending on whether the mobile host initiated a rekey, and on
whether the peer host itself wants to rekey or verify the mobile whether the peer host itself wants to rekey or verify the mobile
host's new address, a number of responses are possible. Figure 3 host's new address, a number of responses are possible. Figure 4
illustrates an exchange for which neither side initiates a illustrates an exchange for which neither side initiates a
rekeying, but for which the peer host performs an address check. rekeying, but for which the peer host performs an address check.
If the peer host chooses not to perform an address check, the If the peer host chooses not to perform an address check, the
UPDATE that it sends will only acknowledge the mobile host's UPDATE that it sends will only acknowledge the mobile host's
update but will not solicit a response from the mobile host. If update but will not solicit a response from the mobile host. If
the mobile host is rekeying, the peer will also rekey, as shown the mobile host is rekeying, the peer will also rekey, as shown
in Figure 4. If the mobile host did not decide to rekey but the in Figure 5. If the mobile host did not decide to rekey but the
peer desires to do so, then it initiates a rekey as illustrated peer desires to do so, then it initiates a rekey as illustrated
in Figure 5. The UPDATE messages sent from the peer back to the in Figure 6. The UPDATE messages sent from the peer back to the
mobile are sent to the newly advertised address. mobile are sent to the newly advertised address.
3. If the peer host is verifying the new address, the address is 3. If the peer host is verifying the new address, the address is
marked as UNVERIFIED in the interim. Once it has successfully marked as UNVERIFIED in the interim. Once it has successfully
received a reply to its UPDATE challenge, or optionally, data on received a reply to its UPDATE challenge, or optionally, data on
the new SA, it marks the new address as ACTIVE and removes the the new SA, it marks the new address as ACTIVE and removes the
old address. old address.
Mobile Host Peer Host Mobile Host Peer Host
UPDATE(REA, SEQ) UPDATE(LOC, SEQ)
-----------------------------------> ----------------------------------->
UPDATE(SPI, SEQ, ACK, ECHO_REQUEST) UPDATE(SPI, SEQ, ACK, ECHO_REQUEST)
<----------------------------------- <-----------------------------------
UPDATE(ACK, ECHO_RESPONSE) UPDATE(ACK, ECHO_RESPONSE)
-----------------------------------> ----------------------------------->
Figure 3: Readdress without rekeying, but with address check Figure 4: Readdress without rekeying, but with address check
Mobile Host Peer Host Mobile Host Peer Host
UPDATE(REA, NES, SEQ, [DIFFIE_HELLMAN]) UPDATE(LOC, NES, SEQ, [DIFFIE_HELLMAN])
-----------------------------------> ----------------------------------->
UPDATE(NES, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST) UPDATE(NES, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST)
<----------------------------------- <-----------------------------------
UPDATE(ACK, ECHO_RESPONSE) UPDATE(ACK, ECHO_RESPONSE)
-----------------------------------> ----------------------------------->
Figure 4: Readdress with mobile-initiated rekey Figure 5: Readdress with mobile-initiated rekey
Mobile Host Peer Host Mobile Host Peer Host
UPDATE(REA, SEQ) UPDATE(LOC, SEQ)
-----------------------------------> ----------------------------------->
UPDATE(NES, SEQ, ACK, [DIFFIE_HELLMAN], ECHO_REQUEST) UPDATE(NES, SEQ, ACK, [DIFFIE_HELLMAN], ECHO_REQUEST)
<----------------------------------- <-----------------------------------
UPDATE(NES, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_RESPONSE) UPDATE(NES, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_RESPONSE)
-----------------------------------> ----------------------------------->
UPDATE(ACK) UPDATE(ACK)
<----------------------------------- <-----------------------------------
Figure 5: Readdress with peer-initiated rekey Figure 6: Readdress with peer-initiated rekey
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 REA parameter. or via the LOCATOR parameter.
5.2 Host multihoming 6.2 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. The host may notify the peer host of the additional interface. The host may notify the peer host of the additional
interface(s) by using the REA parameter. To avoid problems with the interface(s) by using the LOCATOR parameter. To avoid problems with
ESP reordering window, a host SHOULD use a different SA for each the ESP anti-replay window, a host SHOULD use a different SA for each
interface used to receive packets from the peer host. interface used to receive packets from the peer host.
When more than one address is provided to the peer host, the host When more than one locator is provided to the peer host, the host
SHOULD indicate which address is preferred. By default, the SHOULD indicate which locator is preferred. By default, the
addresses used in the base exchange are preferred until indicated addresses used in the base exchange are preferred until indicated
otherwise. otherwise.
Although the protocol may allow for configurations in which there is Although the protocol may allow for configurations in which there is
an asymmetric number of SAs between the hosts (e.g., one host has two an asymmetric number of SAs between the hosts (e.g., one host has two
interfaces and two inbound SAs, while the peer has one interface and interfaces and two inbound SAs, while the peer has one interface and
one inbound SA), it is RECOMMENDED that inbound and outbound SAs be one inbound SA), it is RECOMMENDED that inbound and outbound SAs be
created pairwise between hosts. When a NES arrives to rekey a created pairwise between hosts. When a NES 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.
To add both an additional interface and SA, the host sends a REA with To add both an additional interface and SA, the host sends a LOCATOR
a NES. The host uses the same (new) SPI value in the REA and both with a NES. The host uses the same (new) SPI value in the LOCATOR
the "Old SPI" and "New SPI" values in the NES-- this indicates to the and both the "Old SPI" and "New SPI" values in the NES-- this
peer that the SPI is not replacing an existing SPI. The multihomed indicates to the peer that the SPI is not replacing an existing SPI.
host transitions to state REKEYING, waiting for a NES from the peer The multihomed host transitions to state REKEYING, waiting for a NES
and an ACK of its own UPDATE. As in the mobility case, the peer host from the peer and an ACK of its own UPDATE. As in the mobility case,
can perform an address check while it is rekeying. Figure 6 the peer host can perform an address check while it is rekeying.
illustrates the basic packet exchange. Figure 7 illustrates the basic packet exchange.
Multi-homed Host Peer Host Multi-homed Host Peer Host
UPDATE(REA, NES, SEQ, [DIFFIE_HELLMAN]) UPDATE(LOC, NES, SEQ, [DIFFIE_HELLMAN])
-----------------------------------> ----------------------------------->
UPDATE(NES, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST) UPDATE(NES, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST)
<----------------------------------- <-----------------------------------
UPDATE(ACK, ECHO_RESPONSE) UPDATE(ACK, ECHO_RESPONSE)
-----------------------------------> ----------------------------------->
Figure 6: Basic multihoming scenario Figure 7: Basic multihoming scenario
For the case in which multiple addresses are advertised in a REA, the For the case in which multiple locators are advertised in a LOCATOR,
peer does not need to send ACK for the UPDATE(REA) in every the peer does not need to send ACK for the UPDATE(LOCATOR) in every
subsequent message used for the address check procedure of the subsequent message used for the address check procedure of the
multiple addresses. Therefore, a sample packet exchange might look multiple locators. Therefore, a sample packet exchange might look as
as shown in Figure 7. shown in Figure 8.
Multi-homed Host Peer Host Multi-homed Host Peer Host
UPDATE(REA(addr_1,addr_2), SEQ) UPDATE(LOC(addr_1,addr_2), SEQ)
-----------------------------------> ----------------------------------->
UPDATE(ACK) UPDATE(ACK)
<----------------------------------- <-----------------------------------
sent to addr_1:UPDATE(SPI, SEQ, ECHO_REQUEST) sent to addr_1:UPDATE(SPI, SEQ, ECHO_REQUEST)
<----------------------------------- <-----------------------------------
UPDATE(ACK, ECHO_RESPONSE) UPDATE(ACK, ECHO_RESPONSE)
-----------------------------------> ----------------------------------->
sent to addr_2:UPDATE(SPI, SEQ, ECHO_REQUEST) sent to addr_2:UPDATE(SPI, SEQ, ECHO_REQUEST)
<----------------------------------- <-----------------------------------
UPDATE(ACK, ECHO_RESPONSE) UPDATE(ACK, ECHO_RESPONSE)
-----------------------------------> ----------------------------------->
Figure 7: REA with multiple addresses Figure 8: LOCATOR with multiple addresses
When processing inbound REAs that establish new security When processing inbound LOCATORs that establish new security
associations, a host uses the destination address of the UPDATE associations, a host uses the destination address of the UPDATE
containing REA as the local address to which the REA plus NES is containing LOCATOR as the local address to which the LOC plus NES is
targeted. Hosts may send REA with the same IP address to different targeted. Hosts may send LOCATOR with the same IP address to
peer addresses-- this has the effect of creating multiple inbound SAs different peer addresses-- this has the effect of creating multiple
implicitly affiliated with different source addresses. inbound SAs implicitly affiliated with different source addresses.
When rekeying in a multihoming situation in which there is an When rekeying in a multihoming situation in which there is an
asymmetric number of SAs between two hosts, a respondent to the NES/ asymmetric number of SAs between two hosts, a respondent to the NES/
UPDATE procedure may have some ambiguity as to which inbound SA it UPDATE procedure may have some ambiguity as to which inbound SA it
should update in response to the peer's UPDATE. In such a case, the should update in response to the peer's UPDATE. In such a case, the
host SHOULD choose an SA corresponding to the inbound interface on host SHOULD choose an SA corresponding to the inbound interface on
which the UPDATE was received. which the UPDATE was received.
5.3 Site multi-homing 6.3 Site multi-homing
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 5.2. Note that a single addresses, described above in Section 6.2. Note that a single
interface may experience site multi-homing while the host itself may interface may experience site multi-homing 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 to further align it with the requirements of the extensions to HIP to further align it with the requirements of the
multi6 working group. multi6 working group.
5.4 Dual host multi-homing 6.4 Dual host multi-homing
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 8, consider address after the base exchange completes. In Figure 9, consider
that host1 wants to add address addr1b. It would send a REA to host2 that host1 wants to add address addr1b. It would send a LOCATOR to
located at addr2a, and a new set of SPIs would be added between hosts host2 located at addr2a, and a new set of SPIs would be added between
1 and 2 (call them SPI1b and SPI2b). Next, consider host2 deciding hosts 1 and 2 (call them SPI1b and SPI2b). Next, consider host2
to add addr2b to the relationship. host2 now has a choice of which deciding to add addr2b to the relationship. host2 now has a choice
of host1's addresses to initiate REA to. It may choose to initiate a of which of host1's addresses to initiate LOCATOR to. It may choose
REA to addr1a, addr1b, or both. If it chooses to send to both, then to initiate a LOCATOR to addr1a, addr1b, or both. If it chooses to
a full mesh (four SA pairs) of SAs would exist between the two hosts. send to both, then a full mesh (four SA pairs) of SAs would exist
This is the most general case; it may be often the case that hosts between the two hosts. This is the most general case; it may be
primarily establish new SAs only with the peer's preferred address. often the case that hosts primarily establish new SAs only with the
The readdressing protocol is flexible enough to accommodate this peer's preferred locator. The readdressing protocol is flexible
choice. enough to accommodate this choice.
-<- SPI1a -- -- SPI2a ->- -<- SPI1a -- -- SPI2a ->-
host1 < > addr1a <---> addr2a < > host2 host1 < > addr1a <---> addr2a < > host2
->- SPI2a -- -- SPI1a -<- ->- SPI2a -- -- SPI1a -<-
addr1b <---> addr2b addr1b <---> addr2b
Figure 8: Dual multihoming case in which each host uses REA to add a Figure 9: Dual multihoming case in which each host uses LOCATOR to
second address add a second address
5.5 Combined mobility and multi-homing 6.5 Combined mobility and multi-homing
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 REA plus NES should be flexible enough to handle most such The use of LOCATOR plus NES should be flexible enough to handle most
scenarios, although more complicated scenarios have not been studied such scenarios, although more complicated scenarios have not been
so far. studied so far.
5.6 Network renumbering 6.6 Using LOCATORs across addressing realms
It is possible for HIP associations to migrate to a state in which
both parties are only using locators in different addressing realms.
For example, the two hosts may initiate the HIP association when both
are using IPv6 locators, then one host may loose its IPv6
connectivity and obtain an IPv4 address. In such a case, some type
of mechanism for interworking between the different realms must be
employed; such techniques are outside the scope of the present text.
If no mechanism exists, then the UPDATE message carrying the new
LOCATOR will likely not be acknowledged anyway, and the HIP state may
time out.
6.7 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.
5.7 Initiating the protocol in R1 or I2 6.8 Initiating the protocol in R1 or I2
A Responder host MAY include one or more REA parameters in the R1 A Responder host MAY include one or more LOCATOR parameters in the R1
packet that it sends to the Initiator. These parameters MUST be packet that it sends to the Initiator. These parameters MUST be
protected by the R1 signature. If the R1 packet contains REA protected by the R1 signature. If the R1 packet contains LOCATOR
parameters, the Initiator SHOULD send the I2 packet to the new parameters, the Initiator SHOULD send the I2 packet to the new
preferred address. The I1 destination address and the new preferred preferred locator. The I1 destination address and the new preferred
address may be identical. locator may be identical.
Initiator Responder Initiator Responder
R1 with REA R1 with LOCATOR
<----------------------------------- <-----------------------------------
record additional addresses record additional addresses
change responder address change responder address
I2 with new SPI in SPI parameter I2 with new SPI in SPI parameter
-----------------------------------> ----------------------------------->
(process normally) (process normally)
R2 R2
<----------------------------------- <-----------------------------------
(process normally) (process normally)
Figure 9: REA inclusion in R1 Figure 10: LOCATOR inclusion in R1
An Initiator MAY include one or more REA parameters in the I2 packet, An Initiator MAY include one or more LOCATOR parameters in the I2
independent on whether there was REA parameter(s) in the R1 or not. packet, independent on whether there was LOCATOR parameter(s) in the
These parameters MUST be protected by the I2 signature. Even if the R1 or not. These parameters MUST be protected by the I2 signature.
I2 packet contains REA parameters, the Responder MUST still send the Even if the I2 packet contains LOCATOR parameters, the Responder MUST
R2 packet to the source address of the I2. The new preferred address still send the R2 packet to the source address of the I2. The new
SHOULD be identical to the I2 source address. preferred locator SHOULD be identical to the I2 source address.
Initiator Responder Initiator Responder
I2 with REA I2 with LOCATOR
-----------------------------------> ----------------------------------->
(process normally) (process normally)
record additional addresses record additional addresses
R2 with new SPI in SPI parameter R2 with new SPI in SPI parameter
<----------------------------------- <-----------------------------------
(process normally) (process normally)
data on new SA data on new SA
------------------------------------> ------------------------------------>
(process normally) (process normally)
Figure 10: REA inclusion in I2 Figure 11: LOCATOR inclusion in I2
6. Parameter and packet formats
6.1 REA parameter
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 3
Length: Length in octets, excluding Type and Length fields.
SPI: Security Parameter Index (SPI) corresponding to Addresses
P: Preferred address. Set to one if the first address in this REA is
the new preferred address; otherwise set to zero.
Reserved: Zero when sent, ignored when received.
Address Lifetime: Address lifetime, in seconds.
Address: An IPv6 address or an IPv4-in-IPv6 format IPv4 address [2].
The SPI field identifies the SPI that this parameter applies to. It
is implicitly qualified by the Host Identity of the sending host.
The sending host is free to introduce new SPIs at will. That is, if
a received REA has a new SPI, it means that all the old addresses,
assigned to the other SPIs, are also supposed to still work, while
the new addresses in the newly received REA are supposed to be
associated with a new SPI. On the other hand, if a received REA has
an SPI that the receiver already knows about, it would replace (all)
the address(es) currently associated with the SPI with the new
one(s).
The Address Lifetime indicates how long the following address is
expected to be valid. The lifetime is expressed in seconds. Each
address MUST have a non-zero lifetime. The address is expected to
become deprecated when the specified number of seconds has passed
since the reception of the message. A deprecated address SHOULD NOT
be used as an destination address if an alternate (non-deprecated) is
available and has sufficient scope. Since IP addresses are ignored
upon reception, deprecation status does not have any affect on the
receiver.
The Address field contains an IPv6 address, or an IPv4 address in the
IPv4-in-IPv6 format [2]. The latter format denotes a plain IPv4
address that can be used to reach the Mobile Host.
6.2 UPDATE packet with included REA
A number of combinations of parameters in an UPDATE packet are
possible (e.g., see Section 5). Any UPDATE packet that includes a
REA parameter SHOULD include both an HMAC and a HIP_SIGNATURE
parameter.>
If there are multiple REA parameters to be sent in a single UPDATE,
and at least one of the REA parameters is matched with a NES
parameter, then each REA must be matched with a NES parameter, to
avoid ambiguity:
IP ( HIP ( REA1, REA2, NES1, NES2, [ DH, ] ... ) )
If there are multiple REA parameters to be sent and not all are
paired with a NES, then multiple UPDATEs must be used (some with NES,
some without) to avoid ambiguity in the pairing of REA with NES.
7. Processing rules 7. Processing rules
7.1 Sending REAs 7.1 Sending LOCATORs
The decision of when to send REAs is basically a local policy issue. The decision of when to send LOCATORs is basically a local policy
However, it is RECOMMENDED that a host sends a REA whenever it issue. However, it is RECOMMENDED that a host sends a LOCATOR
recognizes a change of its IP addresses, and assumes that the change whenever it recognizes a change of its IP addresses, and assumes that
is going to last at least for a few seconds. Rapidly sending the change is going to last at least for a few seconds. Rapidly
conflicting REAs SHOULD be avoided. sending conflicting LOCATORs 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, and addresses, it has to decide how to group the various addresses, and
whether to include any addresses on multiple SPIs. Since each SPI is whether to include any addresses on multiple SPIs. Since each SPI is
associated with a different Security Association, the grouping policy associated with a different Security Association, the grouping policy
may be based on IPsec replay protection considerations. In the may be based on ESP anti-replay protection considerations. In the
typical case, simply basing the grouping on actual kernel level typical case, simply basing the grouping on actual kernel level
physical and logical interfaces is often the best policy. Virtual physical and logical interfaces is often the best policy. Virtual
interfaces, such as IPsec tunnel interfaces or Mobile IP home interfaces, such as IPsec tunnel interfaces or Mobile IP home
addresses SHOULD NOT be announced. addresses SHOULD NOT be announced.
Note that the purpose of announcing IP addresses in a REA 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 (and therefore virtual interfaces) provide sub-optimal tunnels (and therefore virtual interfaces) provide sub-optimal
connectivity. Furthermore, it should be possible to replace most connectivity. Furthermore, it should be possible to replace most
tunnels with HIP based "non-tunneling", therefore making most virtual tunnels with HIP based "non-tunneling", therefore making most virtual
interfaces fairly unnecessary in the future. On the other hand, interfaces fairly unnecessary in the future. On the other hand,
there are clearly situations where tunnels are used for diagnostic there are clearly situations where tunnels are used for diagnostic
and/or testing purposes. In such and other similar cases announcing and/or testing purposes. In such and other similar cases announcing
the IP addresses of virtual interfaces may be appropriate. the IP addresses of virtual interfaces may be appropriate.
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 REA parameter for each group. If there are to the SPIs, it creates a LOCATOR parameter for each group. If there
multiple REA parameters, the parameters MUST be ordered so that the are multiple LOCATOR parameters, the parameters MUST be ordered so
new preferred address is in the first REA parameter. Only one that the new preferred locator is in the first LOCATOR parameter.
address (the first one, if at all) may be indicated as preferred in Only one locator (the first one, if at all) may be indicated as
the REA parameter. preferred for each distinct Traffic Type in the LOCATOR parameter.
If addresses are being added to an existing SPI, the REA parameter If addresses are being added to an existing SPI, the LOCATOR
indicates the existing SPI and the full set of valid addresses for parameter includes the full set of valid addresses for that SPI, each
that SPI. Any addresses previously ACTIVE on that SPI that are not using a Locator Type of "1" and each with the same value for SPI.
included in the REA will be set to DEPRECATED by the receiver. Any locators previously ACTIVE on that SPI that are not included in
the LOCATOR will be set to DEPRECATED by the receiver.
If a mobile host decides to change the SPI upon a readdress, it sends If a mobile host decides to change the SPI upon a readdress, it sends
a REA with the SPI field within the REA set to the new SPI, and also a LOCATOR with the SPI field within the LOCATOR set to the new SPI,
a NES parameter with the Old SPI field set to the previous SPI and and also a NES parameter with the Old SPI field set to the previous
the New SPI field set to the new SPI. If multiple REA and NES SPI and the New SPI field set to the new SPI. If multiple LOCATOR
parameters are included, the NES MUST be ordered such that they and NES parameters are included, the NES MUST be ordered such that
appear in the same order as the set of corresponding REAs. The they appear in the same order as the set of corresponding LOCATORs.
decision as to whether to rekey and send a new Diffie-Hellman The decision as to whether to rekey and send a new Diffie-Hellman
parameter while performing readdressing is a local policy decision. parameter while performing readdressing is a local policy decision.
If new addresses and new SPIs are being created, the REA parameter's If new addresses and new SPIs are being created, the LOCATOR
SPI field contains the new SPI, and the NES parameter's the Old SPI parameter's SPI field contains the new SPI, and the NES parameter's
field and New SPI fields are both set to the new SPI, indicating that Old SPI field and New SPI fields are both set to the new SPI,
this is a new and not a replacement SPI. indicating that this is a new and not a replacement SPI.
If there are multiple REA parameters leading to a packet size that If there are multiple LOCATOR parameters leading to a packet size
exceeds the MTU, the host SHOULD send multiple packets, each smaller that exceeds the MTU, the host SHOULD send multiple packets, each
than the MTU. In the case of R1 and I2, the additional packets smaller than the MTU. In the case of R1 and I2, the additional
should be UPDATE packets that are sent after the base exchange has packets should be UPDATE packets that are sent after the base
been completed. exchange has been completed.
7.2 Handling received REAs 7.2 Handling received LOCATORs
A host SHOULD be prepared to receive REA parameters in any HIP A host SHOULD be prepared to receive LOCATOR parameters in any HIP
packets, excluding I1. packets, excluding I1.
When a host receives a REA parameter, it first performs the following When a host receives a LOCATOR parameter, it first performs the
operations: following operations:
1. The host checks if the SPI listed is a new one. If it is a new 1. For each locator listed in the LOCATOR parameter, check that the
one, it creates a new SPI that contains no addresses. If it is address therein is a legal unicast or anycast address. That is,
an existing one, it prepares to change the address set on the the address MUST NOT be a broadcast or multicast address. Note
existing SPI. that some implementations MAY accept addresses that indicate the
2. For each address listed in the REA parameter, check that the local host, since it may be allowed that the host runs HIP with
address is a legal unicast or anycast address. That is, the itself.
address MUST NOT be a broadcast or multicast address. Note that 2. For each address listed in the LOCATOR parameter, check if the
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 address listed in the REA parameter, check if the
address is already bound to the SPI. If the address is already address is already bound to the SPI. If the address is already
bound, its lifetime is updated. If the status of the address is bound, its lifetime is updated. If the status of the address is
DEPRECATED, the status is changed to UNVERIFIED. If the address DEPRECATED, the status is changed to UNVERIFIED. If the address
is not already bound, the address is added, and its status is set is not already bound, the address is added, and its status is set
to UNVERIFIED. Mark all addresses on the SPI that were NOT to UNVERIFIED. Mark all addresses on the SPI that were NOT
listed in the REA parameter as DEPRECATED. As a result, the SPI listed in the LOCATOR parameter as DEPRECATED. As a result, the
now contains any addresses listed in the REA parameter either as SPI now contains any addresses listed in the LOCATOR parameter
UNVERIFIED or ACTIVE, and any old addresses not listed in the REA either as UNVERIFIED or ACTIVE, and any old addresses not listed
parameter as DEPRECATED. in the LOCATOR parameter as DEPRECATED.
4. If the REA is paired with a NES parameter, the NES parameter is 3. If the LOCATOR is paired with a NES parameter, the NES parameter
processed. If the REA is replacing the address on an existing is processed. If the LOCATOR is replacing the address on an
SPI, the SPI itself may be changed-- in this case, the host existing SPI, the SPI itself may be changed-- in this case, the
proceeds according to HIP rekeying procedures. This case is host proceeds according to HIP rekeying procedures. This case is
indicated by the NES parameter including an existing SPI in the indicated by the NES parameter including an existing SPI in the
Old SPI field and a new SPI in the New SPI field, and the SPI Old SPI field and a new SPI in the New SPI field, and the SPI
field in the REA matching the New SPI in the NES. If instead the field in the LOCATOR matching the New SPI in the NES. If instead
REA corresponds to a new SPI, the NES will include the same SPI the LOCATOR corresponds to a new SPI, the NES will include the
in both its Old SPI and New SPI fields. same SPI in both its Old SPI and New SPI fields.
5. Mark all addresses at the address group that were NOT listed in
the REA parameter as DEPRECATED.
Once the host has updated the SPI, if the REA parameter contains a 4. Mark all locators at the address group that were NOT listed in
new preferred address, the host SHOULD initiate a change of the the LOCATOR parameter as DEPRECATED.
preferred address. This usually requires that the host first
verifies reachability of the address, and only then changes the Once the host has updated the SPI, if the LOCATOR parameter contains
preferred address. See Section 7.4. a new preferred locator, the host SHOULD initiate a change of the
preferred locator. This usually requires that the host first
verifies reachability of the associated address, and only then
changes the preferred locator. See Section 7.4.
7.3 Verifying address reachability 7.3 Verifying address reachability
A host MAY want to verify the reachability of any UNVERIFIED address A host MAY want to verify the reachability of any UNVERIFIED address
at any time. It typically does so by sending a nonce to the new at any time. It typically does so by sending a nonce to the new
address. For example, if the host is changing its SPI and is sending address. For example, if the host is changing its SPI and is sending
a NES to the peer, the new SPI value SHOULD be random and the value a NES to the peer, the new SPI value SHOULD be random and the value
MAY be copied into an ECHO_REQUEST sent in the rekeying UPDATE. If MAY be copied into an ECHO_REQUEST sent in the rekeying UPDATE. If
the host is not rekeying, it MAY still use the ECHO_REQUEST parameter the host is not rekeying, it MAY still use the ECHO_REQUEST parameter
in an UPDATE message sent to the new address. A host MAY also use in an UPDATE message sent to the new address. A host MAY also use
other message exchanges as confirmation of the address reachability. other message exchanges as confirmation of the address reachability.
Note that in the case of receiving a REA on an R1 and replying with Note that in the case of receiving a LOCATOR on an R1 and replying
an I2, receiving the corresponding R2 is sufficient for marking the with an I2, receiving the corresponding R2 is sufficient for marking
Responder's primary address active. the Responder's primary address active.
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,
instead of waiting for the confirmation via a HIP packet (e.g., instead of waiting for the confirmation via a HIP packet (e.g.,
Figure 13). In this case, a host advertising a new SPI as part of Figure 12). 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. Marking the address active as a part of receiving
data on the SA is an idempotent operation, and does not cause any data on the SA is an idempotent operation, and does not cause any
harm. harm.
Mobile host Peer host Mobile host Peer host
prepare incoming SA prepare incoming SA
new SPI in R2, or UPDATE new SPI in R2, or 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 13: Address activation via use of new SA Figure 12: Address activation via use of new SA
7.4 Changing the preferred address 7.4 Changing the preferred locator
A host MAY want to change the preferred outgoing address for A host MAY want to change the preferred outgoing locator for
different reasons, e.g., because traffic information or ICMP error different reasons, e.g., because traffic information or ICMP error
messages indicate that the currently used preferred address may have messages indicate that the currently used preferred address may have
become unreachable. Another reason is receiving a REA parameter that become unreachable. Another reason is receiving a LOCATOR parameter
has the P-bit set. that has the P-bit set.
To change the preferred address, the host initiates the following To change the preferred locator, the host initiates the following
procedure: procedure:
1. If the new preferred address has ACTIVE status, the preferred 1. If the new preferred locator has ACTIVE status, the preferred
address is changed and the procedure succeeds. locator is changed and the procedure succeeds.
2. If the new preferred address has UNVERIFIED status, the host 2. If the new preferred locator has UNVERIFIED status, the host
starts to verify its reachability. Once the verification has starts to verify its reachability. Once the verification has
succeeded, the preferred address change is completed, unless a succeeded, the preferred locator change is completed, unless a
new change has been initiated in the meantime. new change has been initiated in the meantime.
3. If the peer host has not indicated a preference for any address, 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 then the host picks one of the peer's ACTIVE addresses randomly
or according to policy. This case may arise if, for example, or according to policy. This case may arise if, for example,
ICMP error messages arrive that deprecate the preferred address, ICMP error messages arrive that deprecate the preferred locator,
but the peer has not yet indicated a new preferred address. but the peer has not yet indicated a new preferred locator.
4. If the new preferred address has DEPRECATED status and there is 4. If the new preferred locator has DEPRECATED status and there is
at least one non-deprecated address, the host selects one of the at least one non-deprecated address, the host selects one of the
non-deprecated addresses as a new preferred address and non-deprecated addresses as a new preferred locator and
continues. continues.
8. Policy considerations 8. Policy considerations
XXX: This section needs to be written. XXX: This section needs to be written.
The host may change the status of unused ACTIVE addresses into The host may change the status of unused ACTIVE addresses into
UNVERIFIED after a locally configured period of inactivity. UNVERIFIED after a locally configured period of inactivity.
9. Security Considerations 9. Security Considerations
XXX: This section requires lots of more work. Text contribution expected from Greg Perkins
(Initial text by Jari Arkko): If not controlled in some manner,
messaging related to address changes would create the following types
of vulnerabilities:
Revealing the contents of the (cleartext) communications
Hijacking communications and man-in-the-middle attacks
Denial of service for the involved nodes, by disabling their
ability to receive the desired communications
Denial of service for third parties, by redirecting a large amount
of traffic to them
Revealing the location of the nodes to other parties
In HIP, communications are bound to the public keys of the end-points
and not to IP addresses. The REA message is signed with the sender's
public key, and hence it becomes impossible to hijack the
communications of another host through the use of the REA message.
Similarly, since only the host itself can sign messages to move its
traffic flows to a new IP address, denial of service attacks through
REA can not cause the traffic flows to be sent to an IP address that
the host did not wish to use. Finally, in HIP all communications are
encrypted with ESP, so a hijack attempt would also be unable to
reveal the contents of the communications.
Malicious nodes that use HIP can, however, try to cause a denial of
service attack by establishing a high-volume traffic flow, such as a
video stream, and then redirecting it to a victim. However, the
address reachability check provides some assurance that the given
address is willing to accept the new traffic. Only attackers who are
on the path between the peer and the new address could respond to the
test.
10. IANA Considerations 10. IANA Considerations
11. Acknowledgments 11. Acknowledgments
12. References 12. References
12.1 Normative references 12.1 Normative references
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-01
(work in progress), October 2004.
[2] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
(ESP)", RFC 2406, November 1998.
[3] Moskowitz, R., "Host Identity Protocol Architecture",
draft-ietf-hip-arch-02 (work in progress), January 2005.
[4] 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.
[2] Hinden, R. and S. Deering, "IP Version 6 Addressing [5] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998. Architecture", RFC 2373, July 1998.
[3] Moskowitz, R., Nikander, P. and P. Jokela, "Host Identity [6] Jokela, P., "Host Identity Protocol", draft-ietf-hip-esp-00
Protocol", draft-moskowitz-hip-09 (work in progress), February (work in progress), February 2005.
2004.
[4] Moskowitz, R., "Host Identity Protocol Architecture",
draft-moskowitz-hip-arch-05 (work in progress), October 2003.
12.2 Informative references 12.2 Informative references
[5] Bellovin, S., "EIDs, IPsec, and HostNAT", IETF 41th, March 1998. [7] Bellovin, S., "EIDs, IPsec, and HostNAT", IETF 41th, March 1998.
[6] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on [8] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on
Security Considerations", draft-iab-sec-cons-00 (work in Security Considerations", draft-iab-sec-cons-00 (work in
progress), August 2002. progress), August 2002.
[7] Nikander, P., "Mobile IP version 6 Route Optimization Security [9] Nikander, P., "Mobile IP version 6 Route Optimization Security
Design Background", draft-nikander-mobileip-v6-ro-sec-02 (work Design Background", draft-nikander-mobileip-v6-ro-sec-02 (work
in progress), December 2003. in progress), December 2003.
Authors' Addresses Authors' Addresses
Pekka Nikander Pekka Nikander
Ericsson Research Nomadic Lab Ericsson Research Nomadic Lab
JORVAS FIN-02420 JORVAS FIN-02420
FINLAND FINLAND
skipping to change at page 32, line 5 skipping to change at page 33, line 5
reachable address. reachable address.
Clarified whether REAs sent for existing SPIs update the full set of Clarified whether REAs sent for existing SPIs update the full set of
addresses associated with that SPI, or only perform an incremental addresses associated with that SPI, or only perform an incremental
(additive) update. REAs for an existing SPI should list all current (additive) update. REAs for an existing SPI should list all current
addresses for that SPI, and any addresses previously in use on the addresses for that SPI, and any addresses previously in use on the
SPI but not in the new REA parameter should be DEPRECATED. SPI but not in the new REA parameter should be DEPRECATED.
Clarified that address verification pertains to *outgoing* addresses. Clarified that address verification pertains to *outgoing* addresses.
When discussing incluson of REA in I2, the draft stated "The When discussing inclusion of REA in I2, the draft stated "The
Responder MUST make sure that the puzzle solution is valid BOTH for Responder MUST make sure that the puzzle solution is valid BOTH for
the initial IP destination address used for I1 and for the new the initial IP destination address used for I1 and for the new
preferred address." However, this statement conflicted with Appendix preferred address." However, this statement conflicted with Appendix
D of the base specification, so it has been removed for now. D of the base specification, so it has been removed for now.
Appendix B. Implementation experiences A.4 From draft-ietf-hip-mm-00 to -01
Introduction section reorganized. Some of the scope of the document
relating to multihoming was reduced.
Removed empty appendix "Implementation experiences"
Renamed REA parameter to LOCATOR and aligned to the discussion on
redefining this parameter that occurred on the RG mailing list.
Aligned with decoupling of ESP from base spec.
Intellectual Property Statement Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
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This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
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