Internet DRAFT - draft-ietf-mpls-deprecate-bgp-entropy-label
draft-ietf-mpls-deprecate-bgp-entropy-label
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
draft-ietf-mpls-deprecate-bgp-entropy-label-02
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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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.
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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
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
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
Email: jgs@juniper.net
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Kireeti Kompella
Juniper Networks
Email: kireeti@juniper.net
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