Network Working Group                                        S. Bellovin
Internet-Draft                                       Columbia University
Intended status: Standards Track                                 R. Bush
Expires: September 12, 2012                    Internet Initiative Japan
                                                                 D. Ward
                                                           Cisco Systems
                                                          March 11, 2012

             Security Requirements for BGP Path Validation


   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",
   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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 12, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal

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   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Recommended Reading . . . . . . . . . . . . . . . . . . . . . . 3
   3.  General Requirements  . . . . . . . . . . . . . . . . . . . . . 3
   4.  BGP UPDATE Security Requirements  . . . . . . . . . . . . . . . 6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
   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

   As noted in the threat model, [I-D.ietf-sidr-bgpsec-threats], this
   work is limited to threats to the BGP protocol.  Issues of business
   relationship confomance, of which routing 'leaks' are a subset, while
   important are outside the scope of the working group and therefore
   this document.  It is hoped that these issues will be better
   understood in the future.

2.  Recommended Reading

   This document assumes knowledge of the RPKI see [RFC6480], the RPKI
   Repository Structure, see [RFC6481].

   This document assumes ongoing incremental deployment of ROAs, see
   [RFC6482], 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

   3.2   A BGPsec design must allow the receiver of an announcement to
         detect if an AS has added or deleted any AS number other than
         its own in the path attribute.  This includes modification to
         the number of AS prepends.

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   3.3   A BGPsec design MUST be amenable to incremental deployment.
         Any incompatible protocol capabilities MUST be negotiated.

   3.4   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..

   3.5   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.

   3.6   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.

   3.7   A BGPsec design MUST resist attacks by an enemy who has access
         to the inter-router link layer, per Section 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
         TCP-AO [RFC5925], IPsec [RFC4301], or TLS [RFC5246].

   3.8   It is assumed that a BGPsec design will require information
         about holdings of address space and ASNs, and assertions about
         binding of address space to ASNs.  A BGPsec design MAY make use
         of a security infrastructure (e.g., a PKI) to distribute such
         authenticated data.

   3.9   [ this point should probably be removed. it remains to keep
         numbering for the moment ] If message signing increases message
         size, the 4096 byte limit on BGP PDU size MAY be removed, see

   3.10  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.ietf-idr-deprecate-as-sets].

   3.11  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.

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   3.12  A BGPsec design MUST enable each BGPsec speaker to configure
         use of the security mechanism on a per-peer basis.

   3.13  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.

   3.14  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].

   3.15  A BGPsec design MUST support 'transparent' route servers,
         meaning that the AS of the route server is not counted in
         downstream BGP AS-path-length tie-breaking decisions.

   3.16  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,

   3.17  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.

   3.18  A BGPsec design SHOULD flag security exceptions which are
         significant enough to be logged.  The specific data to be
         logged are an implementation matter.

   3.19  Any routing information database MUST be re-authenticated
         periodically or in an event-driven manner, especially in
         response to events such as, for example, PKI updates.

   3.20  Any inter-AS use of cryptographic hashes or signatures, MUST
         provide mechanisms for algorithm agility.

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   3.21  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.

   3.22  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

   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

   4.5  NLRI of the UPDATE message SHOULD be able to be authenticated 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 unequivocal and conform to a fully
        specified state in the design.

5.  IANA Considerations

   This document asks nothing of the IANA.

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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.

8.  References

8.1.  Normative References

              Kent, S. and A. Chi, "Threat Model for BGP Path Security",
              draft-ietf-sidr-bgpsec-threats-02 (work in progress),
              February 2012.

   [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.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, June 2010.

8.2.  Informative References

              Patel, K. and R. Bush, "Extended Message support for BGP",
              draft-ietf-idr-bgp-extended-messages-02 (work in
              progress), January 2012.

              Kumari, W. and K. Sriram, "Recommendation for Not Using
              AS_SET and AS_CONFED_SET in BGP",
              draft-ietf-idr-deprecate-as-sets-06 (work in progress),
              October 2011.

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              Christian, B. and T. Tauber, "BGP Security Requirements",
              draft-ietf-rpsec-bgpsecrec-10 (work in progress),
              November 2008.

              Reynolds, M. and S. Kent, "Local Trust Anchor Management
              for the Resource Public Key Infrastructure",
              draft-ietf-sidr-ltamgmt-04 (work in progress),
              December 2011.

              Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
              Austein, "BGP Prefix Origin Validation",
              draft-ietf-sidr-pfx-validate-03 (work in progress),
              October 2011.

              Bush, R. and R. Austein, "The RPKI/Router Protocol",
              draft-ietf-sidr-rpki-rtr-26 (work in progress),
              February 2012.

   [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.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, February 2012.

   [RFC6481]  Huston, G., Loomans, R., and G. Michaelson, "A Profile for
              Resource Certificate Repository Structure", RFC 6481,
              February 2012.

   [RFC6482]  Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
              Origin Authorizations (ROAs)", RFC 6482, February 2012.

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Authors' Addresses

   Steven M. Bellovin
   Columbia University
   1214 Amsterdam Avenue, MC 0401
   New York, New York  10027

   Phone: +1 212 939 7149

   Randy Bush
   Internet Initiative Japan
   5147 Crystal Springs
   Bainbridge Island, Washington  98110

   Phone: +1 206 780 0431 x1

   David Ward
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134


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