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Versions: 00 01 02 03 draft-ietf-idr-next-hop-capability

Network Working Group                                        B. Decraene
Internet-Draft                                                    Orange
Updates: 6790 (if approved)                                  K. Kompella
Intended status: Standards Track                  Juniper Networks, Inc.
Expires: July 30, 2017                                     W. Henderickx
                                                                   Nokia
                                                        January 26, 2017


                  BGP Next-Hop dependant capabilities
               draft-decraene-idr-next-hop-capability-03

Abstract

   RFC 5492 defines capabilities advertisement for the BGP peer.  In
   addition, it is useful to be able to advertise BGP Next-Hop dependant
   capabilities, in particular for forwarding plane features.  RFC 5492
   is not applicable because the BGP peer may be different from the BGP
   Next-Hop, in particular when BGP Route Reflection is used.  This
   document defines a mechanism to advertise such BGP Next Hop dependant
   Capabilities.

   This document defines a new BGP non-transitive attribute to carry
   Next-Hop Capabilities.  This attribute is deleted or possibly
   modified when the BGP Next Hop is changed.

   This document also defines a Next-Hop capability to advertise the
   ability to handle the MPLS Entropy Label defined in RFC 6790.  It
   updates RFC 6790 with regard to this BGP signaling.

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].

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 http://datatracker.ietf.org/drafts/current/.

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



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   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 July 30, 2017.

Copyright Notice

   Copyright (c) 2017 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  BGP Next-Hop dependant Capabilities Attribute . . . . . . . .   3
     2.1.  Encoding  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Attribute Operation . . . . . . . . . . . . . . . . . . .   4
     2.3.  Capability Code Operation . . . . . . . . . . . . . . . .   5
     2.4.  Attribute Error Handling  . . . . . . . . . . . . . . . .   5
   3.  Entropy Label Next-Hop dependant Capability . . . . . . . . .   6
     3.1.  Entropy Label Next-Hop Capability error handling  . . . .   7
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Next-Hop Capabilities Attribute . . . . . . . . . . . . .   7
     4.2.  Next-Hop Capability registry  . . . . . . . . . . . . . .   7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   [RFC5492] defines capabilities advertisement for the BGP peer.  In
   addition, it is useful to be able to advertise BGP Next-Hop dependant
   capabilities, in particular for forwarding plane features.  RFC 5492
   is not applicable because the BGP peer may be different from the BGP
   Next-Hop, in particular when BGP Route Reflection is used.  This




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   document defines a mechanism to advertise such BGP Next Hop
   Capabilities.

   This document defines a new BGP non-transitive attribute to carry
   Next-Hop Capabilities.  When the BGP Next Hop is changed, this
   attribute is deleted or possibly modified to take into account the
   capabilities of the new BGP Next-Hop. Hence it allows advertising
   capabilities which are dependent of the BGP Next-Hop.

   This attribute advertises the capabilities of the BGP Next-Hop for
   the NLRI advertised in the same BGP update.  A BGP Next-Hop may
   advertise different capabilities for different set of NLRI.

   This document also defines a first application to advertise the
   capability to handle the MPLS Entropy Label defined in [RFC6790].
   Note that RFC 6790 had originally defined a BGP attribute for this
   but it has been latter deprecated in [RFC7447].

2.  BGP Next-Hop dependant Capabilities Attribute

2.1.  Encoding

   The BGP Next-Hop dependant Capabilities Attribute is an optional,
   non-transitive BGP Attribute, of value TBD1.  The attribute consists
   of a set of Next-Hop Capabilities.

   The inclusion of a Next-Hop Capability "X" in a BGP UPDATE message,
   indicates that the BGP Next-Hop, encoded in either the NEXT_HOP
   attribute defined in [RFC4271] or the Network Address of Next Hop
   field of the MP_REACH_NLRI attribute defined in [RFC4760], supports
   the capability "X" for the NLRI advertised in this BGP UPDATE.

   This document does not make a distinction between these two Next-Hop
   fields and uses the term 'BGP Next-Hop' to refer to whichever one is
   used in a given BGP UPDATE message.

   A Next-Hop Capability is a triple (Capability Code, Capability
   Length, Capability Value) aka a TLV:













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                     +------------------------------+
                     | Capability Code (1 octet)    |
                     +------------------------------+
                     | Capability Length (1 octet)  |
                     +------------------------------+
                     | Capability Value (variable)  |
                     ~                              ~
                     +------------------------------+

                     Figure 1: BGP Next-Hop Capability

   Capability Code: a one-octet unsigned binary integer which indicates
   the type of "Next-Hop Capability" advertised and unambiguously
   identifies an individual capability.

   Capability Length: a one-octet unsigned binary integer which
   indicates the length, in octets, of the Capability Value field.  A
   length of 0 indicates that no Capability Value Field is present.

   Capability Value: a variable-length field from 0 to 255 octets.  It
   is interpreted according to the value of the Capability Code.

   BGP speakers SHOULD NOT include more than one instance of a Next-Hop
   capability with the same Capability Code, Capability Length, and
   Capability Value.  Note, however, that processing of multiple
   instances of such capability does not require special handling, as
   additional instances do not change the meaning of the announced
   capability; thus, a BGP speaker MUST be prepared to accept such
   multiple instances.

   BGP speakers MAY include more than one instance of a capability (as
   identified by the Capability Code) with non-zero Capability Length
   field, but with different Capability Value and either the same or
   different Capability Length.  Processing of these capability
   instances is specific to the Capability Code and MUST be described in
   the document introducing the new capability.

2.2.  Attribute Operation

   The BGP Next-Hop dependant Capabilities attribute being non-
   transitive, as per [RFC4271], a BGP speaker which does not understand
   it will quietly ignore it and not pass it along to other BGP peers.

   A BGP speaker that understands the BGP Next-Hop dependant
   Capabilities Attribute and does not change the BGP Next-Hop, SHOULD
   NOT change the BGP Next-Hop dependant Capabilities Attribute and
   SHOULD pass the attribute unchanged along to other BGP peers.




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   A BGP speaker that understands the BGP Next-Hop dependant
   Capabilities Attribute and changes the BGP Next-Hop, MUST remove the
   received BGP Next-Hop dependant Capabilities Attribute before
   propagating the BGP UPDATE to other BGP peers.  It MAY attach a new
   BGP Next-Hop dependant Capabilities attribute describing the
   capabilities of the new BGP Next-Hop for these NLRIs.

2.3.  Capability Code Operation

   A BGP speaker receiving a BGP Next-Hop Capability Code that it
   supports behave as defined in the document defining this Capability
   Code.  A BGP speaker receiving a BGP Next-Hop Capability Code that it
   does not support MUST ignore this BGP Next-Hop Capability Code.  In
   particular, this MUST NOT be handled as an error.  In both cases, the
   BGP speaker MUST examine the remaining BGP Next-Hop Capability
   Code(s) that may be present in the BGP Next-Hop Capabilities
   Attribute.

   The BGP Next-Hop Capability Code MUST reflect the capability of the
   router indicated in the BGP Next-Hop, for the NLRI advertised in the
   BGP UPDATE.  If a BGP speaker sets the BGP Next-Hop to an address of
   a different router (e.g.  R), it MUST NOT advertise BGP Next-Hop
   Capabilities not supported by this router R for these NLRI.

   The presence of a Next-Hop Capability SHOULD NOT influence route
   selection or route preference of a route, unless tunneling is used to
   reach the BGP Next-Hop or the selected route has been learnt from
   EBGP (i.e. the Next-Hop is in a different AS).  Indeed, it is in
   general impossible for a node to know that all BGP routers of the
   Autonomous System (AS) will understand a given Next-Hop Capability;
   and having different routers, within an AS, use a different
   preference for a route, may result in forwarding loops if tunnelling
   is not used to reach the BGP Next-Hop.

   An implementations MAY allow, by configuration, removing this
   attribute or specific Next-Hop capabilities when advertising the
   routes over EBGP.

2.4.  Attribute Error Handling

   A BGP Next-Hop dependant Capabilities Attribute is considered
   malformed if the length of the Attribute is not equal to the sum of
   all (BGP Next-Hop dependant Capability Length +2) of the capabilities
   carried in this attribute.  Note that "2" is the length of the fields
   "Type" and "Length" of each BGP Next Hop dependant Capability, as the
   capability length only account for the length of the Value field.





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   A document that specifies a new Next-Hop Capability SHOULD provide
   specifics regarding what constitutes an error for that Next-Hop
   Capability.

   A BGP UPDATE message with a malformed BGP Next-Hop dependant
   Capabilities Attribute SHALL be handled using the approach of
   "attribute discard" defined in [RFC7606].

   Unknown Next-Hop Capabilities Codes MUST NOT be considered as an
   error.  They MUST be silently ignored.

   If a Next-Hop dependant Capability is malformed, this Next-Hop
   Capability Type MUST be ignored.  Others Next-Hop Capabilities MUST
   be processed as usual.

3.  Entropy Label Next-Hop dependant Capability

   The Entropy Label Next-Hop Capability has type code 1 and a length of
   0 or 1 octet.

   The inclusion of the "Entropy Label" Next-Hop Capability indicates
   that the BGP Next-Hop can be sent packets, for all routes indicated
   in the NRLI, with a MPLS entropy label (ELI, EL) added immediately
   after the label stack advertised with the NLRI.

   On the receiving side, suppose BGP speaker S has determined that
   packet P is to be forwarded according to BGP route R, where R is a
   route of one of the labeled address families.  And suppose that L is
   the label stack embedded in the NLRI of route R.  Then to forward
   packet P according to route R, S either replaces P's top label with
   L, or else pushes L onto the MPLS label stack.  If the EL-Capability
   is advertised in the BGP UPDATE advertising this route R, S knows
   that it may safely place the ELI and an EL on the label stack
   immediately beneath L.

   A BGP speaker S that sends an UPDATE with the BGP Next-Hop "NH" MAY
   include the Entropy Label Next-Hop Capability only if the NLRI are
   labelled and for all the NLRI in the BGP UPDATE, either of the
   following is true:

   o  Egress case: NH is the egress of the LSP advertised with the NLRI
      and its capable of handling the ELI during the lookup of the MPLS
      top label.

   o  Transit LSR case: NH is a transit LSR for the LSP advertised with
      the NLRI (i.e.  NH swaps one of the label advertised in the NLRI)
      and next downstream BGP Next-Hop(s) has(have) advertised the
      Entropy Label Next-Hop Capability (or a similar capability



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      signalled by protocol P if the route is redistributed, by NH, from
      protocol P to BGP).

3.1.  Entropy Label Next-Hop Capability error handling

   If the Entropy Label Next-Hop Capability is present more than once,
   it MUST be considered as received once with a length of 0.

   If the Entropy Label Next-Hop Capability is received with a length
   other than 0 or 1, it is not considered malformed, but its semantics
   are exactly the same as if it had a length of 1.  In other words,
   additional octets MUST be ignored.  This is to allow for graceful
   future extension.

4.  IANA Considerations

4.1.  Next-Hop Capabilities Attribute

   IANA is requested to allocate a new Path Attribute, called "Next-Hop
   Capabilities", type Code TBD1, from the "BGP Path Attributes"
   registry.

4.2.  Next-Hop Capability registry

   The IANA is requested to create and maintain a registry entitled
   "Next-Hop Capabilities".

   The registration policies [RFC5226] for this registry are:

        1-63   IETF Review
      64-127   First Come First Served
     128-250   Standards Action
     251-254   Experimental Use
         255   Reserved

   IANA is requested to make the following initial assignments:

               Registry Name: Next-Hop Capability.

    Value      Meaning                                  Reference
    ---------- ---------------------------------------- ---------
          0    Reserved  (not to be allocated)          This document
          1    Entropy Label                            This document
      2-250    Unassigned
    251-254    Experimental                             This document
        255    Reserved (for futur registry extension)  This document





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5.  Security Considerations

   This document does not introduce new security vulnerabilities in BGP.
   Specifically, an operator who is relying on the information carried
   in BGP must have a transitive trust relationship back to the source
   of the information.  Specifying the mechanism(s) to provide such a
   relationship is beyond the scope of this document.  Please refer to
   the Security Considerations section of [RFC4271] for security
   mechanisms applicable to BGP.

6.  Acknowledgement

   The Entropy Label Next-Hop Capability defined in this document is
   based on the ELC BGP attribute defined in section 5.2 of [RFC6790].

   The authors wish to thank John Scudder for the discussions on this
   topic and Eric Rosen for his in-depth review of this document.

   The authors wish to thank Jie Dond for his review and comments.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <http://www.rfc-editor.org/info/rfc4271>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <http://www.rfc-editor.org/info/rfc4760>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <http://www.rfc-editor.org/info/rfc6790>.



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   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
              Patel, "Revised Error Handling for BGP UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,
              <http://www.rfc-editor.org/info/rfc7606>.

7.2.  Informative References

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <http://www.rfc-editor.org/info/rfc5492>.

   [RFC7447]  Scudder, J. and K. Kompella, "Deprecation of BGP Entropy
              Label Capability Attribute", RFC 7447,
              DOI 10.17487/RFC7447, February 2015,
              <http://www.rfc-editor.org/info/rfc7447>.

Authors' Addresses

   Bruno Decraene
   Orange

   Email: bruno.decraene@orange.com


   Kireeti Kompella
   Juniper Networks, Inc.
   1194 N.  Mathilda Avenue
   Sunnyvale, CA  94089
   USA

   Email: kireeti.kompella@gmail.com


   Wim Henderickx
   Nokia
   Copernicuslaan 50
   Antwerp 2018, CA  95134
   Belgium

   Email: wim.henderickx@nokia.com











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