





Internet Engineering Task Force (IETF)                         C. Petrie
Request for Comments: 8050                                      RIPE NCC
Category: Standards Track                                        T. King
ISSN: 2070-1721                                                   DE-CIX
                                                                May 2017


 Multi-Threaded Routing Toolkit (MRT) Routing Information Export Format
                  with BGP Additional Path Extensions

Abstract

   This document extends the Multi-threaded Routing Toolkit (MRT) export
   format for Border Gateway Protocol (BGP) routing information by
   supporting the advertisement of multiple paths in BGP extensions.

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 in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc8050.

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.







Petrie & King                Standards Track                    [Page 1]

RFC 8050            Additional Path Extensions in MRT           May 2017


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Rationale . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  MRT Subtypes for Types BGP4MP/BGP4MP_ET . . . . . . . . . . .   3
   4.  MRT Subtypes for Type TABLE_DUMP_V2 . . . . . . . . . . . . .   3
     4.1.  AFI/SAFI-Specific RIB Subtypes  . . . . . . . . . . . . .   4
     4.2.  RIB_GENERIC_ADDPATH Subtype . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  BGP4MP/BGP4MP_ET Subtype Codes  . . . . . . . . . . . . .   5
     5.2.  TABLE_DUMP_V2 Subtype Codes . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The MRT record format [RFC6396] was developed to provide researchers
   and engineers a means to encapsulate, export, and archive routing
   protocol transactions and RIB snapshots.

   The Advertisement of Multiple Paths in BGP [RFC7911] defines a BGP
   extension to allow the advertisement of multiple paths for the same
   address prefix without the new paths implicitly replacing any
   previous ones.

   This document contains an optional extension to the MRT format
   [RFC6396] and introduces additional definitions of MRT subtype fields
   to permit representation of multiple path advertisements [RFC7911].

2.  Rationale

   MRT parsers are usually stateless.  In order to parse BGP messages
   that contain data structures that depend on the capabilities
   negotiated during the BGP session setup, the MRT subtypes are
   utilized.  The Advertisement of Multiple Paths [RFC7911] extension
   for BGP alters the encoding of the BGP Network Layer Reachability
   Information (NLRI) format for withdraws and announcements.
   Therefore, new BGP4MP/BGP4MP_ET subtypes as defined in [RFC6396] are
   required to signal to an MRT parser how to parse the NLRI.

   In Section 4.3 of the MRT specification [RFC6396], RIB subtypes are
   specified.  Prefix length and prefix fields are encoded in the same
   manner as the BGP NLRI encoding.  In order to support Path Identifier
   information as defined in [RFC7911], new subtypes need to be added.

   The following two sections define the required subtypes.




Petrie & King                Standards Track                    [Page 2]

RFC 8050            Additional Path Extensions in MRT           May 2017


3.  MRT Subtypes for Types BGP4MP/BGP4MP_ET

   This document defines the following new subtypes:

   o  BGP4MP_MESSAGE_ADDPATH

   o  BGP4MP_MESSAGE_AS4_ADDPATH

   o  BGP4MP_MESSAGE_LOCAL_ADDPATH

   o  BGP4MP_MESSAGE_AS4_LOCAL_ADDPATH

   The fields of these message types are identical to the equivalent
   non-additional-path versions specified in Section 4.4 of [RFC6396].
   These enhancements continue to encapsulate the entire BGP message in
   the BGP message field.

4.  MRT Subtypes for Type TABLE_DUMP_V2

   This document defines the following new subtypes:

   o  RIB_IPV4_UNICAST_ADDPATH

   o  RIB_IPV4_MULTICAST_ADDPATH

   o  RIB_IPV6_UNICAST_ADDPATH

   o  RIB_IPV6_MULTICAST_ADDPATH

   o  RIB_GENERIC_ADDPATH

   The fields of these message types are identical to the equivalent
   non-additional-path versions specified in Section 4.3 of [RFC6396].
   However, for the case of the 4 AFI/SAFI-specific RIB subtypes, the
   existing RIB Entries field is redefined as detailed in the sections
   below.















Petrie & King                Standards Track                    [Page 3]

RFC 8050            Additional Path Extensions in MRT           May 2017


4.1.  AFI/SAFI-Specific RIB Subtypes

   In order to preserve the record compaction achieved by using the most
   common subtypes and allow multiple RIB Entries to be stored in a
   single TABLE_DUMP_V2 record, the existing RIB Entries field is
   redefined for use within the new AFI/SAFI-specific RIB subtypes
   defined by this document as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Peer Index            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Originated Time                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Path Identifier                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Attribute Length         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    BGP Attributes... (variable)
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 1: RIB Entries for AFI/SAFI-Specific RIB Subtypes with
                       Support for Additional Paths

   This adds a field to the RIB Entries record to store the Path
   Identifier when used with the RIB_IPV4_UNICAST_ADDPATH,
   RIB_IPV4_MULTICAST_ADDPATH, RIB_IPV6_UNICAST_ADDPATH, and
   RIB_IPV6_MULTICAST_ADDPATH subtypes.

4.2.  RIB_GENERIC_ADDPATH Subtype

   The fields of this subtype are identical to the equivalent non-
   additional-path versions specified in Section 4.3.3 of [RFC6396].
   These fields continue to encapsulate the raw and additional-path-
   enabled AFI/SAFI/NLRI in the record, and the raw attributes in the
   RIB Entries.

   For clarity, the RIB Entries in this subtype are not redefined.












Petrie & King                Standards Track                    [Page 4]

RFC 8050            Additional Path Extensions in MRT           May 2017


5.  IANA Considerations

   IANA has assigned the subtype codes defined below in the "Multi-
   threaded Routing Toolkit (MRT)" registry
   <https://www.iana.org/assignments/mrt>.

5.1.  BGP4MP/BGP4MP_ET Subtype Codes

   The following have been registered in the "BGP4MP Subtype Codes" and
   "BGP4MP_ET Subtype Codes" registries:

      8 BGP4MP_MESSAGE_ADDPATH (RFC 8050)

      9 BGP4MP_MESSAGE_AS4_ADDPATH (RFC 8050)

      10 BGP4MP_MESSAGE_LOCAL_ADDPATH (RFC 8050)

      11 BGP4MP_MESSAGE_AS4_LOCAL_ADDPATH (RFC 8050)

5.2.  TABLE_DUMP_V2 Subtype Codes

   The following have been registered in the "TABLE_DUMP_V2 Subtype
   Codes" registry:

      8 RIB_IPV4_UNICAST_ADDPATH (RFC 8050)

      9 RIB_IPV4_MULTICAST_ADDPATH (RFC 8050)

      10 RIB_IPV6_UNICAST_ADDPATH (RFC 8050)

      11 RIB_IPV6_MULTICAST_ADDPATH (RFC 8050)

      12 RIB_GENERIC_ADDPATH (RFC 8050)

6.  Security Considerations

   It is not believed that this document adds any additional security
   considerations.  However, the security considerations of [RFC6396]
   are equally applicable to this document, because this document
   permits the export of more detailed routing data.

   An organization that uses the MRT format to store their BGP routing
   information should be aware that supporting these extensions permits
   more detailed network path information to be stored and should
   consider the implications of this within their environment.






Petrie & King                Standards Track                    [Page 5]

RFC 8050            Additional Path Extensions in MRT           May 2017


   An organization that peers with public BGP collectors and enables the
   capability for additional paths on a peering session should be aware
   that it is exporting not only its best paths, but potentially other
   paths within its networks.  The BGP peer should consider any and all
   implications of exposing this additional data.

7.  Normative References

   [RFC6396]  Blunk, L., Karir, M., and C. Labovitz, "Multi-Threaded
              Routing Toolkit (MRT) Routing Information Export Format",
              RFC 6396, DOI 10.17487/RFC6396, October 2011,
              <http://www.rfc-editor.org/info/rfc6396>.

   [RFC7911]  Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", RFC 7911,
              DOI 10.17487/RFC7911, July 2016,
              <http://www.rfc-editor.org/info/rfc7911>.

Authors' Addresses

   Colin Petrie
   RIPE NCC
   Stationsplein 11
   Amsterdam  1012 AB
   The Netherlands

   Email: cpetrie@ripe.net


   Thomas King
   DE-CIX Management GmbH
   Lichtstrasse 43i
   Cologne  50825
   Germany

   Email: thomas.king@de-cix.net















Petrie & King                Standards Track                    [Page 6]

