Network Working Group

Internet Engineering Task Force (IETF)                           R. Bush
Internet-Draft
Request for Comments: 8654                                  Arrcus & IIJ
Updates: 4271 (if approved)                                                   K. Patel
Intended status:
Category: Standards Track                                   Arrcus, Inc.
Expires: February 17, 2020
ISSN: 2070-1721                                                  D. Ward
                                                           Cisco Systems
                                                         August 16,
                                                            October 2019

                    Extended Message support Support for BGP
                draft-ietf-idr-bgp-extended-messages-36

Abstract

   The BGP specification (RFC 4271) mandates a maximum BGP message size
   of 4,096 octets.  As BGP is extended to support newer AFI/SAFIs new Address Family
   Identifiers (AFIs), Subsequent AFIs (SAFIs), and other features,
   there is a need to extend the maximum message size beyond 4,096
   octets.  This document updates the BGP specification RFC4271 by extending the
   maximum message size from 4,096 octets to 65,535 octets for all
   messages except the for OPEN and KEEPALIVE messages.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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 an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list  It represents the consensus of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid the IETF community.  It has
   received public review and has been approved for a maximum publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of six months RFC 7841.

   Information about the current status of this document, any errata,
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 17, 2020.
   https://www.rfc-editor.org/info/rfc8654.

Copyright Notice

   Copyright (c) 2019 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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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language
   2.  BGP Extended Message  . . . . . . . . . . . . . . . . . . . .   2
   3.  BGP Extended Message Capability for BGP . . . . . . . . . . . . .   3
   4.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Changes to RFC4271  . . . . . . . . . . . . . . . . . . . . .   5 RFC 4271
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   10.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.
     9.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.
     9.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Acknowledgments
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The BGP specification [RFC4271] mandates a maximum BGP message size
   of 4,096 octets.  As BGP is extended to support newer AFI/SAFIs new AFIs, SAFIs, and
   newer
   other capabilities (e.g., BGPsec [RFC8205] and BGP-LS BGP - Link State (BGP-
   LS) [RFC7752]), there is a need to extend the maximum message size
   beyond 4,096 octets.  This draft document provides an extension to BGP to
   extend its the message size limit from 4,096 octets to 65,535 octets for
   all messages except
   the for OPEN and KEEPALIVE messages.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  BGP Extended Message

   A BGP message over 4,096 octets in length is a BGP Extended Message.

   BGP Extended Messages have a maximum message size of 65,535 octets.
   The smallest message that may be sent consists of is a BGP KEEPALIVE KEEPALIVE, which
   consists of 19 octets.

3.  BGP Extended Message Capability for BGP

   The BGP Extended Message Capability is a new BGP Capability capability [RFC5492]
   defined with Capability code Code 6 and Capability length Length 0.

   To advertise the BGP Extended Message Capability to a peer, a BGP
   speaker uses BGP Capabilities Advertisement [RFC5492].  By
   advertising the BGP Extended Message Capability to a peer, a BGP
   speaker conveys that it is able to receive and properly handle, see
   Section 4, handle BGP
   Extended Messages. Messages (see Section 4).

   Peers that wish to use the BGP Extended Message capability Capability MUST
   support Error Handling error handling for BGP UPDATE Messages messages per [RFC7606].

4.  Operation

   The BGP Extended Message Capability applies to all messages except
   for
   the OPEN and KEEPALIVE messages.  The former exception is to  These exceptions reduce the
   complexity of providing backward compatibility.

   A BGP speaker that is capable of receiving BGP Extended Messages
   SHOULD advertise the BGP Extended Message Capability to its peers
   using BGP Capabilities Advertisement [RFC5492].  A BGP speaker MAY
   send BGP Extended Messages to a peer only if the BGP Extended Message
   Capability was received from that peer.

   An implementation that advertises the BGP Extended Message capability Capability
   MUST be capable of receiving a message with a Length length up to and
   including 65,535 octets.

   Applications generating information which that might be encapsulated within
   BGP messages MUST limit the size of their payload to take the maximum
   message size into account.

   During the years of incremental deployment, speakers that are capable
   of Extended Messages should not simply pack as many NLRI in a message
   as they can, or otherwise unnecessarily generate UPDATES above the
   4,096 octet pre- Extended Message limit, so as not to require
   downstream routers to decompose for peers that do not support
   Extended Messages.  See Section 8.

   If a BGP message with a Length length greater than 4,096 octets is received
   by a BGP listener who has not advertised the BGP Extended Message
   Capability, the listener will generate a NOTIFICATION with the Error
   Subcode set to Bad Message Length ([RFC4271] Sec ([RFC4271], Section 6.1).

   A BGP UPDATE will (policy, (if allowed by policy, best path, etc., allowing) etc.) typically
   propagate throughout the BGP speaking Internet; BGP-speaking Internet and hence to BGP
   speakers which that may not support BGP Extended Messages.  Therefore, an
   announcement in an a BGP Extended Message where the size of the
   attribute set plus the NLRI is larger than 4,096 octets may cause
   lack of reachability.

   A BGP speaker that has advertised the BGP Extended Message capability Capability
   to its peers, peers may receive an UPDATE from one of its peers that
   produces an ongoing announcement that is larger than 4,096 octets.
   When propagating that UPDATE onward to a neighbor which that has not
   advertised the BGP Extended Message capability, Capability, the speaker SHOULD
   try to reduce the outgoing message size by removing attributes
   eligible under the "attribute discard" approach of [RFC7606].  If the
   message is still too big, then it must not be sent to the neighbor
   ([RFC4271], Section 9.2).  Additionally, if the NLRI was previously
   advertised to that peer, it must be withdrawn from service
   ([RFC4271], Section 9.1.3).

   If an Autonomous System (AS) has multiple internal BGP speakers and
   also has multiple external BGP neighbors, to present a consistent
   external view care must be taken to
   ensure a consistent view within the AS. AS in order to present a
   consistent external view.  In the context of BGP Extended Messages, a
   consistent view can only be guaranteed if all the iBGP Internal BGP (iBGP)
   speakers advertise the BGP Extended Message capability. Capability.  If that is
   not the case, then the operator should consider whether or not the
   BGP Extended Message capability Capability should be advertised to external peers or not.
   peers.

   During the incremental deployment of BGP Extended Messages and use of
   the "attribute discard" approach of [RFC7606] in an iBGP mesh, mesh or with eBGP
   External BGP (eBGP) peers, the operator should monitor any routes
   dropped and any discarded attributes.

5.  Error Handling

   A BGP speaker that has the ability to use BGP Extended Messages but
   has not advertised the BGP Extended Messages capability, Message Capability, presumably
   due to configuration, MUST NOT accept an a BGP Extended Message.  A
   speaker MUST NOT implement a more liberal policy accepting BGP
   Extended Messages.

   A BGP speaker that does not advertise the BGP Extended Messages
   capability Message
   Capability might also genuinely not support BGP Extended Messages.
   Such a speaker will follow the error handling error-handling procedures of [RFC4271]
   if it receives an a BGP Extended Message.  Similarly, any speaker that
   treats an improper BGP Extended Message as a fatal error, error MUST follow
   the error
   handling error-handling procedures of [RFC4271].

   The UPDATE Message

   Error Handling, handling for UPDATE messages, as specified in Section 6.3 of
   [RFC4271], is unchanged.  However, if a NOTIFICATION is to be sent to
   a BGP speaker that has not advertised the BGP Extended Message
   Capability, the size of the message MUST NOT exceed 4,096 octets.

   It is RECOMMENDED that BGP protocol developers and implementers are
   conservative in their application and use of BGP Extended Messages.
   Future protocol specifications MUST describe how to handle peers
   which that
   can only accommodate 4,096 octet messages.

6.  Changes to RFC4271 RFC 4271

   [RFC4271] states "The value of the Length field MUST always be at
   least 19 and no greater than 4,096." 4096."  This document changes the latter
   number to 65,535 for all messages except the for OPEN and KEEPALIVE
   messages.

   Section 6.1 of [RFC4271] Sec 6.1, specifies raising an error if the length of
   a message is over 4,096 octets.  For all messages except the for OPEN
   message, and
   KEEPALIVE messages, if the receiver has advertised the BGP Extended Messages
   Message Capability, this document raises that limit to 65,535.

7.  IANA Considerations

   The

   IANA has made an early the following allocation for this new BGP Extended
   Message Capability referring to this document.

   Registry: Capability Codes in the "Capability Codes"
   registry:

   +-------+----------------------+-----------+
   | Value | Description                               Document
   -----    -----------------------------------       -------------          | Reference |
   +=======+======================+===========+
   | 6     | BGP Extended Message                      [this draft] | RFC 8654  |
   +-------+----------------------+-----------+

     Table 1: Addition to "Capability Codes"
                     Registry

8.  Security Considerations

   This extension to BGP does not change BGP's underlying security
   issues;
   issues [RFC4272].

   Due to increased memory requirements for buffering, there may be
   increased exposure to resource exhaustion, intentional or
   unintentional.

   If a remote speaker is able to craft a large BGP Extended Message to
   send on a path where one or more peers do not support BGP Extended
   Messages, peers which that support BGP Extended Messages may may:

   *  act to reduce the outgoing message, see message (see Section 4, and 4) and, in doing so
      so, cause an attack by discarding attributes one or more of its peer
      peers may be expecting.  The attributes eligible under the
      "attribute discard" approach must have no effect on route
      selection or installation [RFC7606].

   If a remote speaker is able to craft a large BGP Extended Message to
   send on a path where one or more peers do not support BGP Extended
   Messages, peers which support BGP Extended Messages may

   *  act to reduce the outgoing message, see message (see Section 4, and 4) and, in doing so
      so, allow a downgrade attack.  This would only affect the
      attacker's message, where 'downgrade' has questionable meaning.

   If a remote speaker is able to craft a large BGP Extended Message to
   send on a path where one or more peers do not support BGP Extended
   Messages, peers which support BGP Extended Messages may

   *  incur resource load (processing, message resizing, etc.) when
      reformatting the large messages.

9.  Acknowledgments

   The authors thank Alvaro Retana for an amazing review, Enke Chen,
   Susan Hares, John Scudder, John Levine, and Job Snijders for their
   input; and Oliver Borchert and Kyehwan Lee for their implementations
   and testing.

10.  References

10.1.

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <http://www.rfc-editor.org/info/rfc4271>.
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <http://www.rfc-editor.org/info/rfc5492>. <https://www.rfc-editor.org/info/rfc5492>.

   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
              Patel, "Revised Error Handling for BGP UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,
              <http://www.rfc-editor.org/info/rfc7606>.
              <https://www.rfc-editor.org/info/rfc7606>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <http://www.rfc-editor.org/info/rfc8174>.

10.2. <https://www.rfc-editor.org/info/rfc8174>.

9.2.  Informative References

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis",
              RFC 4272, DOI 10.17487/RFC4272, January 2006,
              <http://www.rfc-editor.org/info/rfc4272>.
              <https://www.rfc-editor.org/info/rfc4272>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <http://www.rfc-editor.org/info/rfc7752>.
              <https://www.rfc-editor.org/info/rfc7752>.

   [RFC8205]  Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
              Specification", RFC 8205, DOI 10.17487/RFC8205, September
              2017, <https://www.rfc-editor.org/info/rfc8205>.

Acknowledgments

   The authors thank Alvaro Retana for an amazing review; Enke Chen,
   Susan Hares, John Scudder, John Levine, and Job Snijders for their
   input; and Oliver Borchert and Kyehwan Lee for their implementations
   and testing.

Authors' Addresses

   Randy Bush
   Arrcus & IIJ
   5147 Crystal Springs
   Bainbridge Island, Washington WA 98110
   US
   United States of America

   Email: randy@psg.com

   Keyur Patel
   Arrcus, Inc.

   Email: keyur@arrcus.com

   Dave Ward
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA 95134
   US
   United States of America

   Email: dward@cisco.com