Internet Engineering Task Force (IETF)                        J. Scudder
Request for Comments: 7447                                   K. Kompella
Updates: 6790                                           Juniper Networks
Category: Standards Track                                  February 2015
ISSN: 2070-1721


        Deprecation of BGP Entropy Label Capability Attribute

Abstract

  The BGP Entropy Label Capability attribute is defined in RFC 6790.
  Regrettably, it has a bug: although RFC 6790 mandates that routers
  incapable of processing Entropy Labels must remove the attribute,
  fulfillment of this requirement cannot be guaranteed in practice.
  This specification deprecates the attribute.  A forthcoming document
  will propose a replacement.

Status of This Memo

  This is an Internet Standards Track document.

  This document is a product of the Internet Engineering Task Force
  (IETF).  It represents the consensus of the IETF community.  It has
  received public review and has been approved for publication by the
  Internet Engineering Steering Group (IESG).  Further information on
  Internet Standards is available in Section 2 of RFC 5741.

  Information about the current status of this document, any errata,
  and how to provide feedback on it may be obtained at
  http://www.rfc-editor.org/info/rfc7447.

Copyright Notice

  Copyright (c) 2015 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
  Provisions Relating to IETF Documents
  (http://trustee.ietf.org/license-info) 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.





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Table of Contents

  1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
    1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
  2.  Deprecation of ELCA . . . . . . . . . . . . . . . . . . . . .   2
  3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
  4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
  5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   3
    5.1.  Normative References  . . . . . . . . . . . . . . . . . .   3
    5.2.  Informative References  . . . . . . . . . . . . . . . . .   3
  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   4
  Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

  [RFC6790] defines the Entropy Label Capability attribute (ELCA), an
  optional, transitive BGP path attribute.  For correct operation, an
  intermediate node modifying the next hop of a route must remove the
  ELCA unless the node doing so is able to process entropy labels.
  Sadly, this requirement cannot be fulfilled with the ELCA as
  specified, because it is an optional, transitive attribute.  By
  definition, a node that does not support the ELCA will propagate the
  attribute (this is a general property of optional, transitive
  attributes; see [RFC4271]).  But such an ELCA-oblivious node is
  likely to be incapable of processing entropy labels and is exactly
  the node that we desire to remove the attribute!

  This specification updates RFC 6790 by deprecating the version of
  ELCA defined in Section 5.2 of that document.  A forthcoming document
  will propose a replacement.  All other sections of RFC 6790 are
  unchanged.

1.1.  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].

2.  Deprecation of ELCA

  This document deprecates the ELCA path attribute.  This means that
  implementations MUST NOT generate the attribute.  If received, the
  attribute MUST be treated as any other unrecognized optional,
  transitive attribute as per [RFC4271], until and unless the code
  point is reused by some new specification.  (To the authors' best
  knowledge, there are no implementations of ELCA at the time of
  writing.)




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3.  IANA Considerations

  For the reasons given in Section 1, IANA has marked attribute 28 "BGP
  Entropy Label Capability Attribute" in the "BGP Path Attributes"
  registry as "deprecated" and has added a reference to this RFC.

4.  Security Considerations

  ELCA, as defined in Section 5.2 of [RFC6790], has in common with
  other optional, transitive path attributes the property that it will
  be "tunneled" through intervening routers that don't implement the
  relevant specification.  Unfortunately, as discussed elsewhere in
  this document, implementations of ELCA that receive such "tunneled"
  attributes could -- sometimes improperly -- rely on them.  The
  consequence of doing so could be a black hole in the forwarding path
  for the affected routes.  Whether or not this is a new security issue
  is somewhat debatable, since an attacker would have to be part of the
  control-plane path for the route in question in order for the
  attacker to exploit the issue.  Under those circumstances, an
  attacker already has a panoply of mischief-making tools available, as
  discussed in [RFC4272].

  In any case, this document renders any real or imagined security
  issues with ELCA moot, by deprecating it.

5.  References

5.1.  Normative References

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

  [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
             L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
             RFC 6790, November 2012,
             <http://www.rfc-editor.org/info/rfc6790>.

5.2.  Informative References

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

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




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Acknowledgements

  Thanks to Alia Atlas, Bruno Decraene, Martin Djernaes, John Drake,
  Adrian Farrel, Keyur Patel, Ravi Singh, and Kevin Wang for their
  discussion of this issue.

Authors' Addresses

  John G. Scudder
  Juniper Networks

  EMail: [email protected]


  Kireeti Kompella
  Juniper Networks

  EMail: [email protected]

































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