BGP-LS Ext Admin Groups: Distribution of Traffic Engineering Extended Administrative Groups Using the Border Gateway Protocol - Link State (BGP-LS)
A new BGP-LS TLV that carries extended administrative groups, the longer link colors used in traffic engineering.
Tantsura, J., Wang, Z., Wu, Q., and K. Talaulikar, "Distribution of Traffic Engineering Extended Administrative Groups Using the Border Gateway Protocol - Link State (BGP-LS)", RFC 9104, DOI 10.17487/RFC9104, August 2021, <https://www.rfc-editor.org/info/rfc9104>.
@misc{rfc9104,
series = {Request for Comments},
number = 9104,
howpublished = {RFC 9104},
publisher = {RFC Editor},
doi = {10.17487/RFC9104},
url = {https://www.rfc-editor.org/info/rfc9104},
author = {J. Tantsura and Z. Wang and Q. Wu and K. Talaulikar},
title = {{Distribution of Traffic Engineering Extended Administrative Groups Using the Border Gateway Protocol - Link State (BGP-LS)}},
pagetotal = 7,
year = 2021,
month = aug,
} RFC text
Contents
Internet Engineering Task Force (IETF) J. Tantsura
Request for Comments: 9104 Microsoft
Category: Standards Track Z. Wang
ISSN: 2070-1721 Q. Wu
Huawei
K. Talaulikar
Cisco Systems
August 2021
Distribution of Traffic Engineering Extended Administrative Groups
Using the Border Gateway Protocol - Link State (BGP-LS)
Abstract
Administrative groups are link attributes used for traffic
engineering. This document defines an extension to the Border
Gateway Protocol - Link State (BGP-LS) for advertisement of extended
administrative groups (EAGs).
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
https://www.rfc-editor.org/info/rfc9104.
Copyright Notice
Copyright (c) 2021 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
(https://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.
Table of Contents
1. Introduction
1.1. Requirements Language
2. Advertising Extended Administrative Groups in BGP-LS
3. IANA Considerations
4. Manageability Considerations
5. Security Considerations
6. References
6.1. Normative References
6.2. Informative References
Acknowledgments
Authors' Addresses
1. Introduction
Administrative groups (commonly referred to as "colors" or "link
colors") are link attributes that are advertised by link-state
protocols like IS-IS [RFC1195], OSPFv2 [RFC2328], and OSPFv3
[RFC5340]. The Border Gateway Protocol - Link State (BGP-LS)
advertisement of the originally defined (non-extended) administrative
groups is encoded using the Administrative Group (color) TLV 1088 as
defined in [RFC7752].
These administrative groups are defined as a fixed-length 32-bit
bitmask. As networks grew and more use cases were introduced, the
32-bit length was found to be constraining, and hence extended
administrative groups (EAGs) were introduced in [RFC7308].
The EAG TLV (Section 2) is not a replacement for the Administrative
Group (color) TLV; as explained in [RFC7308], both values can
coexist. It is out of scope for this document to specify the
behavior of the BGP-LS consumer [RFC7752].
This document specifies an extension to BGP-LS for advertisement of
the extended administrative groups.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Advertising Extended Administrative Groups in BGP-LS
This document defines an extension that enables BGP-LS speakers to
signal the EAG of links in a network to a BGP-LS consumer of network
topology such as a centralized controller. The centralized
controller can leverage this information in traffic engineering
computations and other use cases. When a BGP-LS speaker is
originating the topology learned via link-state routing protocols
like OSPF or IS-IS, the EAG information of the links is sourced from
the underlying extensions as defined in [RFC7308].
The EAG of a link is encoded in a new Link Attribute TLV [RFC7752]
using the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Administrative Group (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended Administrative Group TLV Format
Where:
Type: 1173
Length: variable length that represents the total length of the
value field in octets. The length value MUST be a multiple of 4.
If the length is not a multiple of 4, the TLV MUST be considered
malformed.
Value: one or more sets of 32-bit bitmasks that indicate the
administrative groups (colors) that are enabled on the link when
those specific bits are set.
3. IANA Considerations
IANA has assigned a code point from the "BGP-LS Node Descriptor, Link
Descriptor, Prefix Descriptor, and Attribute TLVs" registry as
described in the following table.
+============+===============================+===================+
| Code Point | Description | IS-IS TLV/Sub-TLV |
+============+===============================+===================+
| 1173 | Extended Administrative Group | 22/14 |
+------------+-------------------------------+-------------------+
Table 1
4. Manageability Considerations
The new protocol extensions introduced in this document augment the
existing IGP topology information that is distributed via [RFC7752].
Procedures and protocol extensions defined in this document do not
affect the BGP protocol operations and management other than as
discussed in Section 6 ("Manageability Considerations") of [RFC7752].
Specifically, the tests for malformed attributes, to perform
syntactic checks as described in Section 6.2.2 ("Fault Management")
of [RFC7752], now encompass the new BGP-LS Attribute TLV defined in
this document. The semantic or content checking for the TLV
specified in this document and its association with the BGP-LS
Network Layer Reachability Information (NLRI) types or its BGP-LS
Attribute are left to the consumer of the BGP-LS information (e.g.,
an application or a controller) and not to BGP itself.
A consumer of the BGP-LS information retrieves this information over
a BGP-LS session (refer to Sections 1 and 2 of [RFC7752]).
5. Security Considerations
The procedures and protocol extensions defined in this document do
not affect the BGP security model. See the "Security Considerations"
section of [RFC4271] for a discussion of BGP security. This document
only introduces a new Attribute TLV, and any syntactic error in it
would result in the BGP-LS Attribute being discarded [RFC7752].
Also, refer to [RFC4272] and [RFC6952] for analyses of security
issues for BGP. Security considerations for acquiring and
distributing BGP-LS information are discussed in [RFC7752]. The TLV
introduced in this document is used to propagate the EAG extensions
defined in [RFC7308]. It is assumed that the IGP instances
originating this TLV will support any required security mechanisms
for OSPF and IS-IS, in order to prevent any security issues when
propagating the Sub-TLVs into BGP-LS.
Security concerns for OSPF are addressed in [RFC7474], [RFC4552], and
[RFC7166]. Further security analysis for the OSPF protocol is done
in [RFC6863].
Security considerations for IS-IS are specified by [RFC5304].
The advertisement of the link attribute information defined in this
document presents no significant additional risk beyond that
associated with the existing link attribute information already
supported in [RFC7752].
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7308] Osborne, E., "Extended Administrative Groups in MPLS
Traffic Engineering (MPLS-TE)", RFC 7308,
DOI 10.17487/RFC7308, July 2014,
<https://www.rfc-editor.org/info/rfc7308>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
6.2. Informative References
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
<https://www.rfc-editor.org/info/rfc4552>.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304, October
2008, <https://www.rfc-editor.org/info/rfc5304>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC6863] Hartman, S. and D. Zhang, "Analysis of OSPF Security
According to the Keying and Authentication for Routing
Protocols (KARP) Design Guide", RFC 6863,
DOI 10.17487/RFC6863, March 2013,
<https://www.rfc-editor.org/info/rfc6863>.
[RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
BGP, LDP, PCEP, and MSDP Issues According to the Keying
and Authentication for Routing Protocols (KARP) Design
Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
<https://www.rfc-editor.org/info/rfc6952>.
[RFC7166] Bhatia, M., Manral, V., and A. Lindem, "Supporting
Authentication Trailer for OSPFv3", RFC 7166,
DOI 10.17487/RFC7166, March 2014,
<https://www.rfc-editor.org/info/rfc7166>.
[RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
"Security Extension for OSPFv2 When Using Manual Key
Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
<https://www.rfc-editor.org/info/rfc7474>.
Acknowledgments
The authors would like to thank Eric Osborne, Les Ginsberg, Tim
Chown, Ben Niven-Jenkins, and Alvaro Retana for their reviews and
valuable comments.
Authors' Addresses
Jeff Tantsura
Microsoft
Email: jefftant.ietf@gmail.com
Zitao Wang
Huawei
Yuhua District
101 Software Avenue
Nanjing
Jiangsu, 210012
China
Email: wangzitao@huawei.com
Qin Wu
Huawei
Yuhua District
101 Software Avenue
Nanjing
Jiangsu, 210012
China
Email: bill.wu@huawei.com
Ketan Talaulikar
Cisco Systems
Email: ketant@cisco.com
AI ELI5
On this page
§1Introduction
Administrative groups, commonly called colors or link colors, are link attributes advertised by link-state protocols such as IS-IS, OSPFv2 and OSPFv3. In BGP-LS (Border Gateway Protocol - Link State), the original non-extended administrative groups are encoded using the Administrative Group (color) TLV 1088 defined in RFC 7752.
This document specifies an extension to BGP-LS for advertising the extended administrative groups.
Network links can carry colored tags. BGP-LS is a way of reporting the network's map to a planning program, and this note teaches it to report one more kind of tag.
§1.1Why Extended Groups Exist
The original administrative groups are a fixed-length 32-bit bitmask. As networks grew and more use cases appeared, 32 bits became constraining, so extended administrative groups (EAGs) were introduced in RFC 7308.
The new EAG TLV does not replace the Administrative Group (color) TLV. As RFC 7308 explains, both values can coexist. How a BGP-LS consumer behaves is out of scope for this document.
The old tag list only had room for 32 colors. When that ran out, a longer list was created, and the old list stays around alongside it.
§2The EAG TLV
BGP-LS speakers use the new TLV to signal the EAG of links to a consumer of topology data, such as a centralized controller, which can use the information in traffic engineering computations and other use cases. When the speaker originates topology learned from OSPF or IS-IS, the EAG information is taken from the underlying extensions in RFC 7308.
The TLV is a new Link Attribute TLV with Type 1173. The Length is the total length of the value field in octets and MUST be a multiple of 4; if it is not, the TLV MUST be considered malformed. The value is one or more 32-bit bitmasks, and a set bit means the corresponding administrative group (color) is enabled on the link.
The tag list is sent as a labeled package: a label saying what it is, a size, and then the colors in chunks of the same size. If the size is not a whole number of chunks, the package is thrown out as broken.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
TYPE | Type | 2 bytes | 1173 | Code point assigned for the TLV. |
LENGTH | Length | 2 bytes | Length of the value field in octets; MUST be a multiple of 4. | |
EAG | Extended Administrative Group | 4 bytes | One or more 32-bit bitmasks; the field is variable length. |
§3IANA Code Point
IANA has assigned code point 1173 from the 'BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs' registry. Its description is Extended Administrative Group, and it corresponds to IS-IS TLV/Sub-TLV 22/14.
The number 1173 is now officially reserved for this kind of tag list, so nobody else uses it.
§4Manageability
The extension adds to the existing IGP topology information distributed through RFC 7752 and does not affect BGP protocol operations and management, other than as discussed in Section 6 of RFC 7752. The syntactic checks for malformed attributes now cover the new TLV.
Semantic or content checking of the TLV, and its association with BGP-LS NLRI types or attributes, is left to the consumer of the information (an application or controller) and not to BGP itself.
BGP only checks that the package is built correctly. Deciding what the colors mean is up to the planning program that reads them.
§5Security Considerations
The extension does not affect the BGP security model. The document only introduces a new Attribute TLV, and any syntactic error in it would result in the BGP-LS Attribute being discarded. The TLV propagates the EAG extensions from RFC 7308, and the IGP instances originating it are assumed to support any required OSPF and IS-IS security mechanisms.
The advertisement of this link attribute information presents no significant additional risk beyond the link attribute information already supported in RFC 7752.
Sharing these extra tags is no riskier than sharing the other link information already shared, and a broken package is just ignored.