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

The MRT record format was developed to provide researchers and engineers a means to encapsulate, export, and archive routing protocol transactions and routing information base snapshots. The Advertisement of Multiple Paths in BGP 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 and introduces additional definitions of MRT subtype fields to permit representation of multiple path advertisements .

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.

MRT parsers are usually stateless. In order to parse BGP messages which contain data structures that depend on the capabilities negotiated during the BGP session setup, the so-called MRT subtypes are utilized. The Advertisement of Multiple Path extension for BGP alters the encoding of the BGP NLRI format for withdraws and announcements. Therefore new BGP4MP/BGP4MP_ET subtypes as defined in are required to signal to a MRT parser how to parse the NLRI. In section 4.3 of the MRT specification 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 new subtypes need to be added. The following two sections define the required subtypes.

This document defines the following new Subtypes: BGP4MP_MESSAGE_ADDPATH BGP4MP_MESSAGE_AS4_ADDPATH BGP4MP_MESSAGE_LOCAL_ADDPATH 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. These enhancements continues to encapsulate the entire BGP message in the BGP message field.

This document defines the following new Subtypes: RIB_IPV4_UNICAST_ADDPATH RIB_IPV4_MULTICAST_ADDPATH RIB_IPV6_UNICAST_ADDPATH RIB_IPV6_MULTICAST_ADDPATH RIB_GENERIC_ADDPATH The fields of these message types are identical to the equivalent non-additional-path versions specified in section 4.3. 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.

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) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 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.

The fields of this subtype are identical to the equivalent non-additional-path versions specified in section 4.3.3. 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.

This document requests that IANA assign the following subtype codes to the MRT name space:

BGP4MP_MESSAGE_ADDPATH = 8 () BGP4MP_MESSAGE_AS4_ADDPATH = 9 () BGP4MP_MESSAGE_LOCAL_ADDPATH = 10 () BGP4MP_MESSAGE_AS4_LOCAL_ADDPATH = 11 () The values provided above are suggested as they are used in implementations.

RIB_IPV4_UNICAST_ADDPATH = 8 () RIB_IPV4_MULTICAST_ADDPATH = 9 () RIB_IPV6_UNICAST_ADDPATH = 10 () RIB_IPV6_MULTICAST_ADDPATH = 11 () RIB_GENERIC_ADDPATH = 12 () The values provided above are suggested as they are used in implementations.

It is not believed that this document adds any additional security considerations. However, the security considerations of are equally applicable to this document, and 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 additional-paths capability 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.