Request for Comments: 8050
Category: Standards Track
Multi-Threaded Routing Toolkit (MRT) Routing Information Export Format
with BGP Additional Path Extensions
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.
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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
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].
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.
3. MRT Subtypes for Types BGP4MP/BGP4MP_ET
This document defines the following new subtypes:
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:
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.
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.
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:
- BGP4MP_MESSAGE_ADDPATH (RFC 8050)
- BGP4MP_MESSAGE_AS4_ADDPATH (RFC 8050)
5.2. TABLE_DUMP_V2 Subtype Codes
The following have been registered in the "TABLE_DUMP_V2 Subtype Codes" registry:
- RIB_IPV4_UNICAST_ADDPATH (RFC 8050)
- RIB_IPV4_MULTICAST_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.
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>.
Colin Petrie RIPE NCC Stationsplein 11 Amsterdam 1012 AB The Netherlands
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