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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]