Deprecation of BGP Entropy Label Capability Attribute
draft-ietf-mpls-deprecate-bgp-entropy-label-01

Internet Engineering Task Force                               J. Scudder
Internet-Draft                                               K. Kompella
Updates: 6790 (if approved)                             Juniper Networks
Intended status: Standards Track                           July 23, 2014
Expires: January 24, 2015

         Deprecation of BGP Entropy Label Capability Attribute
             draft-ietf-mpls-deprecate-bgp-entropy-label-01

Abstract

   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
   replacement.

Status of This Memo

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Copyright Notice

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   document authors.  All rights reserved.

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   the Trust Legal Provisions and are provided without warranty as
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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.

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
   any implementation done subsequent to the publication of this
   document 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",
   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

   Email: jgs@juniper.net

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   Kireeti Kompella
   Juniper Networks

   Email: kireeti@juniper.net

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