Network Working Group C. Petrie
Internet-Draft RIPE NCC
Intended status: Informational October 11, 2015
Expires: April 13, 2016

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


This document updates the Multi-threaded Routing Toolkit (MRT) export format for Border Gateway Protocol (BGP) routing information by extending it to support the Advertisement of Multiple Paths in BGP extensions.

Status of This Memo

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This Internet-Draft will expire on April 13, 2016.

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Table of Contents

1. Introduction

Researchers and engineers often wish to analyze network behavior by studying routing protocol transactions and routing information base snapshots. To this end, the MRT record format [RFC6396] was developed to encapsulate, export, and archive this information in a standardized data representation.

The Advertisement of Multiple Paths in BGP [I-D.ietf-idr-add-paths] 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. The essence of the extension is that each path is identified by a path identifier in addition to the addres prefix

This memo documents an optional extension to the MRT format RFC6396 [RFC6396] and introduces additional definitions of MRT Subtype fields to permit representation of Multiple Path advertisements

2. 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].

3. Rationale

When a BGP message requires information about the capabilities negotiated during the setup of the BGP session for a parser to interpret the message, this information is carried by the MRT subtypes.

The MRT specification defines the following BGP4MP subtypes:

These indicate to a parser whether the AS_PATH and AGGREGATOR attributes should be interpretted according to the rules in RFC6793 [RFC6793]

Additional Paths in BGP [I-D.ietf-idr-add-paths] alters the encoding of the BGP NLRI format for withdraws and announcements. Therefore new BGP4MP subtypes are required to signal to a parser how to parse the NLRI.

The MRT specification defines the following TABLE_DUMP_V2 subtypes:

The existing TABLE_DUMP_V2 AFI/SAFI-Specific RIB Subtypes specify that the Prefix Length and Prefix fields are encoded in the same manner as the BGP NLRI encoding. These also require new subtypes to retain the path identifier information in Additional Paths.

The TABLE_DUMP_V2 RIB_GENERIC subtype contains a single raw NLRI entry, the encoding of which is defined by the AFI and SAFI. Additional Paths alter the NLRI encoding. Therefore a new subtype is required to indicate the change in NLRI format.

4. MRT Subtypes for Type BGP4MP

This document defines the following new Subtypes:

The fields of these message types are identical to the equivalent non-additional-path versions specified in RFC 6396 [RFC6396], and continues to encapsulate the entire BGP message in the BGP Message field.

5. MRT Subtypes for Type TABLE_DUMP_V2

This document defines the following new Subtypes:

The fields of these message types are identical to the equivalent non-additional-path versions specified in RFC 6396 [RFC6396]. However, for the specific case of the 4 AFI/SAFI specific RIB Subtypes, the existing RIB Entries field is re-defined as detailed in the sections below.

5.1. AFI/SAFI specific RIB Subtypes

In order to preserve the record compaction achieved by using the most common subtypes, and allowing 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 additional-paths support

This adds a field to the RIB Entries record, to store the Path Identifier, when used with the RIB_IPV4_UNICAST_AP, RIB_IPV4_MULTICAST_AP, RIB_IPV6_UNICAST_AP and RIB_IPV6_MULTICAST_AP Subtypes

5.2. RIB_GENERIC_AP Subtype

The fields of this message types is identical to the equivalent non-additional-path versions specified in RFC 6396 [RFC6396], and continues to encapsulate the raw AFI/SAFI/NLRI in the record, and the raw attributes in the RIB Entries.

The RIB entries are unchanged, and should be interpreted according to RFC 6396 [RFC6396]

6. IANA Considerations

This document requests that IANA add the appropriate Type Codes and Subtype Codes (to be assigned). This is currently a placeholder.

7. Security Considerations

It is not believed that this document adds any additional security considerations

However, the security considerations of RFC6396 [RFC6396] are equally applicable to this document, and this document permits the export of more detailed routing data.

An organisation which 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

An network that peers with public BGP collectors, and enable the additional-paths capability on a the peering session, should be aware that they are exporting not only their best paths, but potentially other paths within their network. The BGP peer should consider any implications of exposing this additional data.

8. References

8.1. Normative References

[I-D.ietf-idr-add-paths] Walton, D., Retana, A., Chen, E. and J. Scudder, "Advertisement of Multiple Paths in BGP", Internet-Draft draft-ietf-idr-add-paths-11, October 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[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.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet Autonomous System (AS) Number Space", RFC 6793, DOI 10.17487/RFC6793, December 2012.

8.2. Informative References

[I-D.narten-iana-considerations-rfc2434bis] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", Internet-Draft draft-narten-iana-considerations-rfc2434bis-09, March 2008.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, DOI 10.17487/RFC2629, June 1999.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations", BCP 72, RFC 3552, DOI 10.17487/RFC3552, July 2003.

Author's Address

Colin Petrie RIPE NCC Amsterdam, NL EMail: