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Internet Engineering Task Force (IETF)                        J. ScudderRequest for Comments: 7447                                   K. KompellaUpdates:6790                                           Juniper NetworksCategory: Standards Track                                  February 2015ISSN: 2070-1721Deprecation of BGP Entropy Label Capability AttributeAbstract   The BGP Entropy Label Capability attribute is defined inRFC 6790.   Regrettably, it has a bug: althoughRFC 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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://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 toBCP 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.Scudder & Kompella           Standards Track                    [Page 1]

RFC 7447                   Deprecation of ELCA             February 2015Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .21.1.  Requirements Language . . . . . . . . . . . . . . . . . .22.  Deprecation of ELCA . . . . . . . . . . . . . . . . . . . . .23.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .34.  Security Considerations . . . . . . . . . . . . . . . . . . .35.  References  . . . . . . . . . . . . . . . . . . . . . . . . .35.1.  Normative References  . . . . . . . . . . . . . . . . . .35.2.  Informative References  . . . . . . . . . . . . . . . . .3   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .4   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .41.  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 updatesRFC 6790 by deprecating the version of   ELCA defined inSection 5.2 of that document.  A forthcoming document   will propose a replacement.  All other sections ofRFC 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 inRFC 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.)Scudder & Kompella           Standards Track                    [Page 2]

RFC 7447                   Deprecation of ELCA             February 20153.  IANA Considerations   For the reasons given inSection 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 inSection 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.  References5.1.  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",RFC4272, January 2006,              <http://www.rfc-editor.org/info/rfc4272>.Scudder & Kompella           Standards Track                    [Page 3]

RFC 7447                   Deprecation of ELCA             February 2015Acknowledgements   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: jgs@juniper.net   Kireeti Kompella   Juniper Networks   EMail: kireeti@juniper.netScudder & Kompella           Standards Track                    [Page 4]