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Deprecation of BGP Entropy Label Capability Attribute

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7447.
Authors John Scudder , Kireeti Kompella
Last updated 2015-10-14 (Latest revision 2014-12-12)
Replaces draft-scudder-mpls-deprecate-bgp-entropy-label
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Loa Andersson
Shepherd write-up Show Last changed 2014-10-22
IESG IESG state Became RFC 7447 (Proposed Standard)
Action Holders
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Spencer Dawkins
Send notices to (None)
IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack
Internet Engineering Task Force                               J. Scudder
Internet-Draft                                               K. Kompella
Updates: 6790 (if approved)                             Juniper Networks
Intended status: Standards Track                       December 12, 2014
Expires: June 15, 2015

         Deprecation of BGP Entropy Label Capability Attribute


   RFC 6790 defines the BGP Entropy Label Capability attribute.
   Regrettably, it has a bug: although RFC 6790 mandates that Entropy
   Label-incapable routers must remove the attribute, in practice this
   requirement can't be guaranteed to be fulfilled.  This specification
   deprecates the attribute.  A forthcoming document will propose a

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 June 15, 2015.

Copyright Notice

   Copyright (c) 2014 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
   ( 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

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

1.  Introduction

   [RFC6790] defines the Entropy Label Capability attribute (ELCA), an
   optional, transitive BGP path attribute.  For correct operation, it
   is necessary that an intermediate node modifying the next hop of a
   route must remove the ELCA unless the node so doing 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 also be entropy label-incapable and is exactly the
   one 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

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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
   any implementation MUST NOT generate the attribute.  If received it
   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.)

3.  IANA Considerations

   For the reasons given in Section 1, IANA is requested to mark
   attribute 28 in the "BGP Path Attributes" registry as "deprecated"
   and reference this RFC.

4.  Security Considerations

   ELCA as defined in [RFC6790] S. 5.2, has in common with other
   optional, transitive path attributes the property that it will be
   "tunneled" through intervening routers that don't implement the

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   relevant specification.  Unfortunately, as discussed elsewhere in
   this document, implementations of [RFC6790] S. 5.2 receiving such
   "tunneled" attributes could -- sometimes improperly -- rely on them.
   The consequence of so doing could be a black hole in the forwarding
   path for the affected routes.  Whether this is a new security issue
   or not is somewhat debatable, since to be exploited an attacker would
   have to be part of the control plane path for the route in question,
   and 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.  Acknowledgements

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

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, November 2012.

6.2.  Informative References

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis", RFC
              4272, January 2006.

Authors' Addresses

   John G. Scudder
   Juniper Networks


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   Kireeti Kompella
   Juniper Networks


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