draft-ietf-babel-dtls-02.txt   draft-ietf-babel-dtls-03.txt 
Network Working Group A. Decimo Network Working Group A. Decimo
Internet-Draft IRIF, University of Paris-Diderot Internet-Draft IRIF, University of Paris-Diderot
Updates: 6126bis (if approved) D. Schinazi Updates: 6126bis (if approved) D. Schinazi
Intended status: Standards Track Google LLC Intended status: Standards Track Google LLC
Expires: May 18, 2019 J. Chroboczek Expires: July 12, 2019 J. Chroboczek
IRIF, University of Paris-Diderot IRIF, University of Paris-Diderot
November 14, 2018 January 8, 2019
Babel Routing Protocol over Datagram Transport Layer Security Babel Routing Protocol over Datagram Transport Layer Security
draft-ietf-babel-dtls-02 draft-ietf-babel-dtls-03
Abstract Abstract
The Babel Routing Protocol does not contain any means to authenticate The Babel Routing Protocol does not contain any means to authenticate
neighbours or protect messages sent between them. This documents neighbours or protect messages sent between them. This documents
describes a mechanism to ensure these properties, using Datagram specifies a mechanism to ensure these properties, using Datagram
Transport Layer Security (DTLS). This document updates RFC 6126bis. Transport Layer Security (DTLS). This document updates RFC 6126bis.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 18, 2019. This Internet-Draft will expire on July 12, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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skipping to change at page 2, line 16 skipping to change at page 2, line 16
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Specification of Requirements . . . . . . . . . . . . . . 2 1.1. Specification of Requirements . . . . . . . . . . . . . . 2
1.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 3
2. Operation of the Protocol . . . . . . . . . . . . . . . . . . 3 2. Operation of the Protocol . . . . . . . . . . . . . . . . . . 3
2.1. DTLS Connection Initiation . . . . . . . . . . . . . . . 3 2.1. DTLS Connection Initiation . . . . . . . . . . . . . . . 3
2.2. Protocol Encoding . . . . . . . . . . . . . . . . . . . . 4 2.2. Protocol Encoding . . . . . . . . . . . . . . . . . . . . 4
2.3. Transmission . . . . . . . . . . . . . . . . . . . . . . 4 2.3. Transmission . . . . . . . . . . . . . . . . . . . . . . 4
2.4. Reception . . . . . . . . . . . . . . . . . . . . . . . . 4 2.4. Reception . . . . . . . . . . . . . . . . . . . . . . . . 5
2.5. Neighbour table entry . . . . . . . . . . . . . . . . . . 5 2.5. Neighbour table entry . . . . . . . . . . . . . . . . . . 5
2.6. Simultaneous operation of both Babel over DTLS and 2.6. Simultaneous operation of both Babel over DTLS and
unprotected Babel . . . . . . . . . . . . . . . . . . . . 5 unprotected Babel . . . . . . . . . . . . . . . . . . . . 5
3. Interface Maximum Transmission Unit Issues . . . . . . . . . 5 3. Interface Maximum Transmission Unit Issues . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6 6.1. Normative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . 6 6.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Performance Considerations . . . . . . . . . . . . . 7 Appendix A. Performance Considerations . . . . . . . . . . . . . 8
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 8 Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
The Babel Routing Protocol [RFC6126bis] does not contain any means to The Babel Routing Protocol [RFC6126bis] does not contain any means to
authenticate neighbours or protect messages sent between them. authenticate neighbours or protect messages sent between them.
Because of this, an attacker is able to send maliciously crafted Because of this, an attacker is able to send maliciously crafted
Babel messages which could lead a network to route traffic to an Babel messages which could lead a network to route traffic to an
attacker or to an under-resourced target causing denial of service. attacker or to an under-resourced target causing denial of service.
This documents describes a mechanism to prevent such attacks, using This documents specifies a mechanism to prevent such attacks, using
Datagram Transport Layer Security (DTLS) [RFC6347]. Datagram Transport Layer Security (DTLS) [RFC6347].
1.1. Specification of Requirements 1.1. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
1.2. Applicability 1.2. Applicability
The protocol described in this document protects Babel packets with The protocol described in this document protects Babel packets with
DTLS. As such, it inherits the features offered by DTLS, notably DTLS. As such, it inherits the features offered by DTLS, notably
authentication, integrity, replay protection, confidentiality and authentication, integrity, replay protection, confidentiality and
asymmetric keying. It is therefore expected to be applicable in a asymmetric keying. It is therefore expected to be applicable in a
wide range of environments. wide range of environments.
There exists another mechanism for securing Babel, namely Babel HMAC There exists another mechanism for securing Babel, namely Babel HMAC
authentication [BABEL-HMAC]. HMAC only offers very basic features, authentication [BABEL-HMAC]. HMAC only offers basic features, namely
namely authentication, integrity and replay protection with a small authentication, integrity and replay protection with a small number
number of symmetric keys. of symmetric keys.
Since HMAC authentication is simpler, requires fewer changes to the Since HMAC authentication is simpler, requires fewer changes to the
Babel protocol, and avoids a dependency on DTLS, its use is Babel protocol, and avoids a dependency on DTLS, its use is
RECOMMENDED in deployments where both protocols are equally RECOMMENDED in deployments where both protocols are equally
applicable. applicable.
2. Operation of the Protocol 2. Operation of the Protocol
Babel over DTLS requires some changes to how Babel operates. First, Babel over DTLS requires some changes to how Babel operates. First,
DTLS is a client-server protocol, while Babel is a peer-to-peer DTLS is a client-server protocol, while Babel is a peer-to-peer
protocol. Second, DTLS can only protect unicast communication, while protocol. Second, DTLS can only protect unicast communication, while
Babel packets can be sent over to both unicast and multicast Babel packets can be sent over to both unicast and multicast
destinations. destinations.
2.1. DTLS Connection Initiation 2.1. DTLS Connection Initiation
All Babel over DTLS nodes MUST act as DTLS servers on the "babel- Babel over DTLS operates on a different port than unencrypted Babel.
dtls" port (UDP port TBD), and MUST listen for traffic on the All Babel over DTLS nodes MUST act as DTLS servers on a DTLS port,
unencrypted "babel" port (UDP port 6696). When a Babel node and MUST listen for unencrypted Babel traffic on an unencrypted port,
discovers a new neighbor (generally by receiving an unencrypted which MUST be distinct from the DTLS port. The default port for
multicast Babel packet), it compares the neighbour's IPv6 link-local Babel over DTLS is registered with IANA as the "babel-dtls" port (UDP
address with its own, using network byte ordering. If a node's port TBD), and the unencrypted port is registered as the "babel" port
address is lower than the recently discovered neighbor's address, it (UDP port 6696). Nodes SHOULD use these default ports.
acts as a client and connects to the neighbor. In other words, the
node with the lowest address is the DTLS client for this pairwise When a Babel node discovers a new neighbor (generally by receiving an
relationship. As an example, fe80::1:2 is considered lower than unencrypted multicast Babel packet), it compares the neighbour's IPv6
fe80::2:1. link-local address with its own, using network byte ordering. If a
node's address is lower than the recently discovered neighbor's
address, it acts as a client and connects to the neighbor. In other
words, the node with the lowest address is the DTLS client for this
pairwise relationship. As an example, fe80::1:2 is considered lower
than fe80::2:1.
The node acting as DTLS client initiates its DTLS connection from an The node acting as DTLS client initiates its DTLS connection from an
ephemeral UDP port. Nodes SHOULD ensure that new client DTLS ephemeral UDP port. Nodes SHOULD ensure that new client DTLS
connections use different ephemeral ports from recently used connections use different ephemeral ports from recently used
connections to allow servers to differentiate between the new and old connections to allow servers to differentiate between the new and old
DTLS connections. Alternatively, nodes MAY use DTLS connection DTLS connections. Alternatively, nodes MAY use DTLS connection
identifiers [DTLS-CID] as a higher-entropy mechanism to distinguish identifiers [DTLS-CID] as a higher-entropy mechanism to distinguish
between connections. between connections.
When a node receives a new DTLS connection, it MUST verify the source When a node receives a new DTLS connection, it MUST verify that the
IP address, and reject the connection if the address is not an IPv6 source IP address is an IPv6 link-local address; if it is not, it
link-local address. Nodes MUST use mutual authentication MUST reject the connection. Nodes MUST use mutual authentication
(authenticating both client and server); servers MUST request client (authenticating both client and server); servers MUST request client
authentication by sending a CertificateRequest message. If either authentication by sending a CertificateRequest message. If either
node fails to verify the peer's authentication, it MUST abort the node fails to verify the peer's authentication, it MUST abort the
DTLS handshake. Nodes MUST only negotiate DTLS version 1.2 or DTLS handshake. Nodes MUST only negotiate DTLS version 1.2 or
higher. higher. Nodes MUST use DTLS replay protection to prevent attackers
from replaying stale information. Nodes SHOULD drop packets that
have been reordered by more than several IHU intervals, to avoid
letting attackers make stale information last longer.
2.2. Protocol Encoding 2.2. Protocol Encoding
Babel over DTLS sends all unicast Babel packets protected by DTLS. Babel over DTLS sends all unicast Babel packets protected by DTLS.
The entire Babel packet, from the Magic byte at the start of the The entire Babel packet, from the Magic byte at the start of the
Babel header to the last byte of the Babel packet trailer, is sent Babel header to the last byte of the Babel packet trailer, is sent
protected by DTLS. protected by DTLS.
2.3. Transmission 2.3. Transmission
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any unprotected unicast packets. This ensures the confidentiality of any unprotected unicast packets. This ensures the confidentiality of
the information sent in Babel packets (e.g. the network topology) by the information sent in Babel packets (e.g. the network topology) by
only sending it encrypted by DTLS. Unless some out-of-band neighbor only sending it encrypted by DTLS. Unless some out-of-band neighbor
discovery mechanism is available, nodes SHOULD periodically send discovery mechanism is available, nodes SHOULD periodically send
unprotected multicast Hellos to ensure discovery of new neighbours. unprotected multicast Hellos to ensure discovery of new neighbours.
In order to maintain bidirectional reachability, nodes can either In order to maintain bidirectional reachability, nodes can either
rely entirely on unprotected multicast Hellos, or send protected rely entirely on unprotected multicast Hellos, or send protected
unicast Hellos in addition to the multicast Hellos. unicast Hellos in addition to the multicast Hellos.
Since Babel over DTLS only protects unicast packets, implementors may Since Babel over DTLS only protects unicast packets, implementors may
implement Babel over DTLS by modifying an unprotected implementation implement Babel over DTLS by modifying an implementation of Babel
of Babel, and replacing any TLV sent over multicast with a separate without DTLS support, and replacing any TLV previously sent over
TLV sent over unicast for each neighbour. multicast with a separate TLV sent over unicast for each neighbour.
TLVs previously sent over multicast can be replaced with the same
contents over unicast, with the exception of Hellos as described
above. Some implementations could also change the contents of IHU
TLVs when converting to unicast in order to remove redundant
information.
2.4. Reception 2.4. Reception
Babel over DTLS nodes can receive Babel packets either protected over Babel over DTLS nodes can receive Babel packets either protected over
a DTLS connection, or unprotected directly over the "babel" port. To a DTLS connection, or unprotected directly over the "babel" port. To
ensure the security properties of this mechanism, unprotected packets ensure the security properties of this mechanism, unprotected packets
are treated differently. Nodes MUST silently ignore any unprotected are treated differently. Nodes MUST silently ignore any unprotected
packet sent over unicast. When parsing an unprotected packet, a node packet sent over unicast. When parsing an unprotected packet, a node
MUST silently ignore all TLVs that are not of type Hello. Nodes MUST MUST silently ignore all TLVs that are not of type Hello. Nodes MUST
also silently ignore any unprotected Hello with the Unicast flag set. also silently ignore any unprotected Hello with the Unicast flag set.
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2.5. Neighbour table entry 2.5. Neighbour table entry
It is RECOMMENDED for nodes to associate the state of their DTLS It is RECOMMENDED for nodes to associate the state of their DTLS
connection with their neighbour table. When a neighbour entry is connection with their neighbour table. When a neighbour entry is
flushed from the neighbour table (Appendix A of [RFC6126bis]), its flushed from the neighbour table (Appendix A of [RFC6126bis]), its
associated DTLS state SHOULD be discarded. The node SHOULD send a associated DTLS state SHOULD be discarded. The node SHOULD send a
DTLS close_notify alert to the neighbour if it believes the link is DTLS close_notify alert to the neighbour if it believes the link is
still viable. still viable.
While DTLS provides protection against an attacker that replays valid
packets, DTLS is not able to detect when an active on-path attacker
intercepts valid packets and resends them at a later time. This
attack could be used to make a node believe it has bidirectional
reachability to a neighbour even though that neighbour has
disconnected from the network. To prevent this attack, nodes MUST
discard the DTLS state associated with a neighbour after a finite
time of not receiving valid DTLS packets. This can be implemented
by, for example, discarding a neighbour's DTLS state when its
associated IHU timer fires. Note that relying solely on the receipt
of Hellos is not sufficient as multicast Hellos are sent unprotected.
2.6. Simultaneous operation of both Babel over DTLS and unprotected 2.6. Simultaneous operation of both Babel over DTLS and unprotected
Babel Babel
Implementations MAY implement both Babel over DTLS and unprotected Implementations MAY implement both Babel over DTLS and unprotected
Babel. However, accepting unprotected Babel packets (other than Babel. However, accepting unprotected Babel packets (other than
multicast Hellos) loses the security properties of Babel over DTLS. multicast Hellos) loses the security properties of Babel over DTLS.
A node MAY allow configuration options to allow unprotected Babel on A node MAY allow configuration options to allow unprotected Babel on
some interfaces but not others; this effectively gives nodes on that some interfaces but not others; this effectively gives nodes on that
interface the same access as authenticated nodes, and SHOULD NOT be interface the same access as authenticated nodes, and SHOULD NOT be
done unless that interface has a mechanism to authenticate nodes at a done unless that interface has a mechanism to authenticate nodes at a
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not have the ability to compute the overhead of DTLS and the packet not have the ability to compute the overhead of DTLS and the packet
may be fragmented by lower layers. may be fragmented by lower layers.
4. IANA Considerations 4. IANA Considerations
If this document is approved, IANA is requested to register a UDP If this document is approved, IANA is requested to register a UDP
port number, called "babel-dtls", for use by Babel over DTLS. port number, called "babel-dtls", for use by Babel over DTLS.
5. Security Considerations 5. Security Considerations
The interaction between two Babel peers requires Datagram Transport Confidential interaction between two Babel peers requires Datagram
Layer Security (DTLS) with a cipher suite offering confidentiality Transport Layer Security (DTLS) with a cipher suite offering
protection. The guidance given in [RFC7525] MUST be followed to confidentiality protection. The guidance given in [RFC7525] MUST be
avoid attacks on DTLS. followed to avoid attacks on DTLS.
A malicious client might attempt to perform a high number of DTLS A malicious client might attempt to perform a high number of DTLS
handshakes with a server. As the clients are not uniquely identified handshakes with a server. As the clients are not uniquely identified
by the protocol and can be obfuscated with IPv4 address sharing and by the protocol and can be obfuscated with IPv6 temporary addresses,
with IPv6 temporary addresses, a server needs to mitigate the impact a server needs to mitigate the impact of such an attack. Such
of such an attack. Such mitigation might involve rate limiting mitigation might involve rate limiting handshakes from a given subnet
handshakes from a given subnet or more advanced denial of service or more advanced denial of service avoidance techniques beyond the
avoidance techniques beyond the scope of this document. scope of this document.
6. References 6. References
6.1. Normative References 6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC6126bis] [RFC6126bis]
Chroboczek, J. and D. Schinazi, "The Babel Routing Chroboczek, J. and D. Schinazi, "The Babel Routing
Protocol", Internet Draft draft-ietf-babel-rfc6126bis-07, Protocol", Internet Draft draft-ietf-babel-rfc6126bis-07,
skipping to change at page 6, line 52 skipping to change at page 7, line 29
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
6.2. Informative References 6.2. Informative References
[BABEL-HMAC] [BABEL-HMAC]
Do, C., Kolodziejak, W., and J. Chroboczek, "Babel Do, C., Kolodziejak, W., and J. Chroboczek, "Babel
Cryptographic Authentication", Internet Draft draft-ietf- Cryptographic Authentication", Internet Draft draft-ietf-
babel-hmac-01, November 2018. babel-hmac-03, November 2018.
[DTLS-CID] [DTLS-CID]
Rescorla, E., Tschofenig, H., Fossati, T., and T. Gondrom, Rescorla, E., Tschofenig, H., Fossati, T., and T. Gondrom,
"Connection Identifiers for DTLS 1.2", Internet Draft "Connection Identifiers for DTLS 1.2", Internet Draft
draft-ietf-tls-dtls-connection-id-02, October 2018. draft-ietf-tls-dtls-connection-id-02, October 2018.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J., [RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250, Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
skipping to change at page 8, line 7 skipping to change at page 8, line 29
be several kilobytes), Babel peers can use raw public keys [RFC7250] be several kilobytes), Babel peers can use raw public keys [RFC7250]
or the Cached Information Extension [RFC7924]. The Cached or the Cached Information Extension [RFC7924]. The Cached
Information Extension avoids transmitting the server's certificate Information Extension avoids transmitting the server's certificate
and certificate chain if the client has cached that information from and certificate chain if the client has cached that information from
a previous TLS handshake. TLS False Start [RFC7918] can reduce round a previous TLS handshake. TLS False Start [RFC7918] can reduce round
trips by allowing the TLS second flight of messages trips by allowing the TLS second flight of messages
(ChangeCipherSpec) to also contain the (encrypted) Babel packet. (ChangeCipherSpec) to also contain the (encrypted) Babel packet.
Appendix B. Acknowledgments Appendix B. Acknowledgments
The authors would like to thank Thomas Fossati, Gabriel Kerneis, The authors would like to thank Donald Eastlake, Thomas Fossati,
Antoni Przygienda, Markus Stenberg, Dave Taht, and Martin Thomson for Gabriel Kerneis, Antoni Przygienda, Barbara Stark, Markus Stenberg,
their input and contributions. The performance considerations in Dave Taht, and Martin Thomson for their input and contributions. The
this document were inspired from the ones for DNS over DTLS performance considerations in this document were inspired from the
[RFC8094]. ones for DNS over DTLS [RFC8094].
Authors' Addresses Authors' Addresses
Antonin Decimo Antonin Decimo
IRIF, University of Paris-Diderot IRIF, University of Paris-Diderot
Paris Paris
France France
Email: antonin.decimo@gmail.com Email: antonin.decimo@gmail.com
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