Network Working Group S. Bellovin
Internet-Draft Columbia University
Intended status: Standards Track R. Bush
Expires: September 8, 2011 Internet Initiative Japan, Inc.
D. Ward
Juniper Networks
March 7, 2011
Security Requirements for BGP Path Validation
draft-ymbk-bgpsec-reqs-02
Abstract
This document describes requirements for a future BGP security
protocol design to provide cryptographic assurance that the origin AS
had the right to announce the prefix and to provide assurance of the
AS Path of the announcement.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. This document may not be modified,
and derivative works of it may not be created, and it may not be
published except as an Internet-Draft.
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This Internet-Draft will expire on September 8, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Recommended Reading . . . . . . . . . . . . . . . . . . . . . . 3
3. General Requirements . . . . . . . . . . . . . . . . . . . . . 3
4. BGP UPDATE Security Requirements . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
RPKI-based Origin Validation ([I-D.ietf-sidr-pfx-validate]) provides
a measure of resilience to accidental mis-origination of prefixes.
But it provides neither cryptographic assurance (announcements are
not signed), nor assurance of the AS Path of the announcement.
This document describes requirements to be placed on a BGP security
protocol, herein termed BGPsec, intended to rectify these gaps.
The threat model assumed here is documented in [RFC4593] and
[I-D.kent-bgpsec-threats].
2. Recommended Reading
This document assumes knowledge of the RPKI see [I-D.ietf-sidr-arch]
and the RPKI Repository Structure, see [I-D.ietf-sidr-repos-struct].
This document assumes ongoing incremental deployment of ROAs, see
[I-D.ietf-sidr-roa-format], the RPKI to Router Protocol, see
[I-D.ietf-sidr-rpki-rtr], and RPKI-based Prefix Validation, see
[I-D.ietf-sidr-pfx-validate].
And, of course, a knowledge of BGP [RFC4271] is required.
3. General Requirements
The following are general requirements for a BGPsec protocol:
3.1 A BGPsec design must allow the receiver of a BGP announcement
to determine, to a strong level of certainty, that the received
PATH attribute accurately represents the sequence of eBGP
exchanges that propagated the prefix from the origin AS to the
receiver.
3.2 A BGPsec design MUST be amenable to incremental deployment.
Any incompatible protocol capabilities MUST be negotiated.
3.3 A BGPsec design MUST provide analysis of the operational
considerations for deployment and particularly of incremental
deployment, e.g, contiguous islands, non-contiguous islands,
universal deployment, etc..
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3.4 As cryptographic payloads and memory requirements on routers
are likely to increase, a BGPsec design MAY require use of new
hardware. I.e. compatibility with current hardware abilities
is not a requirement that this document imposes on a solution.
As BGPsec will likely not be rolled out for some years, this
should not be a major problem.
3.5 A BGPsec design need not prevent attacks on data plane traffic.
It need not provide assurance that the data plane even follows
the control plane.
3.6 A BGPsec design MUST resist attacks by an enemy who has access
to the link layer, per Section 3.1.1.2 of [RFC4593]. In
particular, such a design must provide mechanisms for
authentication of all data, including protecting against
message insertion, deletion, modification, or replay.
Mechanisms that suffice include TCP sessions authenticated with
IPsec [RFC4301] or TLS [RFC5246].
3.7 A BGPsec design MAY make use of a security infrastructure
(e.g., a PKI) to distribute authenticated data used as input to
routing decisions. Such data include information about
holdings of address space and ASNs, and assertions about
binding of address space to ASNs.
3.8 If message signing increases message size, the 4096 byte limit
on BGP PDU size MAY be removed.
3.9 It is entirely OPTIONAL to secure AS SETs and prefix
aggregation. The long range solution to this is the
deprecation of AS-SETs, see [I-D.wkumari-deprecate-as-sets].
3.10 If a BGPsec design uses signed prefixes, given the difficulty
of splitting a signed message while preserving the signature,
it need NOT handle multiple prefixes in a single UPDATE PDU.
3.11 A BGPsec design MUST enable each BGPsec speaker to configure
use of the security mechanism on a per-peer basis.
3.12 A BGPsec design MUST provide backward compatibility in the
message formatting, transmission, and processing of routing
information carried through a mixed security environment.
Message formatting in a fully secured environment MAY be
handled in a non-backward compatible manner.
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3.13 While the trust level of an NLRI should be determined by the
BGPsec protocol, local routing preference and policy MUST then
be applied to best path and other decisions. Such mechanisms
MUST conform with [I-D.ietf-sidr-ltamgmt].
3.14 If a BGPsec design makes use of a security infrastructure, that
infrastructure SHOULD enable each network operator to select
the entities it will trust when authenticating data in the
security infrastructure. See, for example,
[I-D.ietf-sidr-ltamgmt].
3.15 A BGPsec design MUST NOT require operators to reveal more than
is currently revealed in the operational inter-domain routing
environment, other than the inclusion of necessary security
credentials to allow others to ascertain for themselves the
necessary degree of assurance regarding the validity of NLRI
received via BGPsec. This includes peering, customer, and
provider relationships, an ISP's internal infrastructure, etc.
It is understood that some data are revealed to the savvy
seeker by BGP, traceroute, etc. today.
3.16 A BGPsec design SHOULD flag security exceptions which are
significant enough to be logged. The specific data to be
logged are an implementation matter.
3.17 Any routing information database MAY be re-authenticated
periodically or in an event-driven manner, especially in
response to events such as, for example, PKI updates.
3.18 Should a BGPsec design use hashes or signatures, it should
provide mechanisms for algorithm agility.
3.19 A BGPsec design SHOULD NOT presume to know the intent of the
originator of a NLRI, nor that of any AS on the AS Path.
3.20 A BGP listener SHOULD NOT trust non-BGPsec markings, such as
communities, across trust boundaries.
4. BGP UPDATE Security Requirements
The following requirements MUST be met in the processing of BGP
UPDATE messages:
4.1 A BGPsec design MUST enable each recipient of an UPDATE to
formally validate that the origin AS in the message is
authorized to originate a route to the prefix(es) in the
message.
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4.2 A BGPsec design MUST enable the recipient of an UPDATE to
formally determine that the NLRI has traversed the AS path
indicated in the UPDATE. Note that this is more stringent than
showing that the path is merely not impossible.
4.3 Replay of BGP UPDATE messages need not be completely prevented,
but a BGPsec design MUST provide a mechanism to control the
window of exposure to replay attacks.
4.4 A BGPsec design SHOULD provide some level of assurance that the
origin of a prefix is still 'alive', i.e. that a monkey in the
middle has not withheld a WITHDRAW message or the effects
thereof.
4.5 NLRI of the UPDATE message SHOULD be able to be authenticated in
real-time as the message is processed.
4.6 Normal sanity checks of received announcements MUST be done,
e.g. verification that the first element of the AS_PATH list
corresponds to the locally configured AS of the peer from which
the UPDATE was received.
4.7 The output of a router applying BGPsec to a received signed
UPDATE MUST be either Valid or Unverified. There should be no
shades of grey.
5. IANA Considerations
This document asks nothing of the IANA.
6. Security Considerations
The data plane may not follow the control plane.
Security for subscriber traffic is outside the scope of this
document, and of BGP security in general. IETF standards for payload
data security should be employed. While adoption of BGP security
measures may ameliorate some classes of attacks on traffic, these
measures are not a substitute for use of subscriber-based security.
7. Acknowledgments
The author wishes to thank the authors of [I-D.ietf-rpsec-bgpsecrec]
from whom we liberally stole, Russ Housley, Geoff Huston, Steve Kent,
Sandy Murphy, John Scudder, Sam Weiler, and a number of others.
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8. References
8.1. Normative References
[I-D.kent-bgpsec-threats]
Kent, S., "Threat Model for BGP Path Security",
draft-kent-bgpsec-threats-01 (work in progress),
February 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4593] Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
Routing Protocols", RFC 4593, October 2006.
8.2. Informative References
[I-D.ietf-rpsec-bgpsecrec]
Christian, B. and T. Tauber, "BGP Security Requirements",
draft-ietf-rpsec-bgpsecrec-10 (work in progress),
November 2008.
[I-D.ietf-sidr-arch]
Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", draft-ietf-sidr-arch-12 (work in
progress), February 2011.
[I-D.ietf-sidr-ltamgmt]
Kent, S. and M. Reynolds, "Local Trust Anchor Management
for the Resource Public Key Infrastructure",
draft-ietf-sidr-ltamgmt-00 (work in progress),
November 2010.
[I-D.ietf-sidr-pfx-validate]
Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
Austein, "BGP Prefix Origin Validation",
draft-ietf-sidr-pfx-validate-01 (work in progress),
February 2011.
[I-D.ietf-sidr-repos-struct]
Huston, G., Loomans, R., and G. Michaelson, "A Profile for
Resource Certificate Repository Structure",
draft-ietf-sidr-repos-struct-07 (work in progress),
February 2011.
[I-D.ietf-sidr-roa-format]
Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
Origin Authorizations (ROAs)",
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draft-ietf-sidr-roa-format-10 (work in progress),
February 2011.
[I-D.ietf-sidr-rpki-rtr]
Bush, R. and R. Austein, "The RPKI/Router Protocol",
draft-ietf-sidr-rpki-rtr-10 (work in progress),
March 2011.
[I-D.wkumari-deprecate-as-sets]
Kumari, W., "Deprecation of BGP AS_SET, AS_CONFED_SET.",
draft-wkumari-deprecate-as-sets-01 (work in progress),
September 2010.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
Authors' Addresses
Steven M. Bellovin
Columbia University
1214 Amsterdam Avenue, MC 0401
New York, New York 10027
US
Phone: +1 212 939 7149
Email: bellovin@acm.org
Randy Bush
Internet Initiative Japan, Inc.
5147 Crystal Springs
Bainbridge Island, Washington 98110
US
Phone: +1 206 780 0431 x1
Email: randy@psg.com
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Dave Ward
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, California 94089-1206
US
Phone: +1-408-745-2000
Email: dward@juniper.net
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