Internet DRAFT - draft-heitz-idr-wklc
draft-heitz-idr-wklc
IDR J. Heitz
Internet-Draft Cisco
Intended status: Standards Track K. Sriram
Expires: 9 September 2023 NIST
B. Dickson
J. Heasly
8 March 2023
BGP Well Known Large Community
draft-heitz-idr-wklc-06
Abstract
A range of BGP Autonomous System Numbers is reserved to create a set
of BGP Well Known Large Communities.
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 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 9 September 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Transitivity . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The Global Administrator field of the BGP Large community [RFC8092]
is an Autonomous System Number (ASN). To create a set of Well Known
Large Communities, a set of ASNs must be reserved for them, such that
a real ASN in the Global Administrator field cannot be mistaken for a
Well Known Large Community.
2. Encoding
Each BGP Well Known Large Community value is encoded as a 12-octet
quantity, 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 1 0 1| T | WKLC ID | Data 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields are as shown below:
T - Transitivity field (2 bits). This is further
described below.
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WKLC ID - Well Known Large Community Identifier (1 octet).
See IANA Considerations. If an experimental type
is used, then it MUST NOT be hard coded in the BGP
speaker software; it MUST be configurable.
Different experiments can then run in the same
network without having to coordinate identifier
assignment during the coding stage.
Data 1,2,3 - A 10 octet value specific to the WKLC. Data 1 is
16 bits long and Data 2 and Data 3 are 32 bits long
each. The data portion is divided into the three
fields only to encourage a canonical representation
that follows [RFC8092]. If any WKLC cannot make
use of this data division, it is free to define
another division.
3. Transitivity
The Large Community path attribute is a transitive attribute. Thus,
BGP speakers that do not implement the transitivity described here
will transit the WKLC regardless. If such a speaker wishes not to
receive a particular large community, it MUST filter it out using
local policy. The transitivity field determines how BGP speakers
transfer the WKLC across real Autonomous System (AS) boundaries. The
values are:
0 - Transitive: The WKLC is transitive across ASes.
1 - Non-transitive: The WKLC is not transitive across ASes.
2 - Administration Transitive: The WKLC is transitive across
ASes under the same administration only. By default, every
AS boundary is also an administration boundary. If an
external BGP session is configured as a non-administrative
boundary, then it will send and receive WKLCs with
transitivity 2, else it will discard the WKLC from the
UPDATE message.
3 - One-time Transitive: The WKLC is transitive across ASes
under the same administration and into an AS under the
neighboring administration, but not into an AS under a
further administration. A BGP speaker that receives a WKLC
with transitivity 3 on an external BGP session on an
administrative boundary SHOULD change the transitivity to 2.
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4. Discussion
A criterion considered important is the number of data octets
available for any WKLC type. This is maximized to 10 at the expense
of ASN space and type space.
8 bits for the type is considered to be plenty. 255 types are more
than enough for WKLC, considering how many extended community types
have been used so far (22 at time of this publication). If a large
set of types, each of which requires less than 10 octets of data, is
required, then they can all be specified under a single type code and
further distinguished by using the Data 1 field as a sub-type. An
equivalent example is the EVPN Extended Community type, which defines
further sub types.
The range of AS numbers currently unallocated by IANA is 399,261 to
4,199,999,999. The WKLC reserves 67,108,864 AS numbers. That still
leaves 4,132,491,874 unallocated AS numbers. For comparison, there
are 94,968,317 AS numbers reserved for private use. Thus, the number
of ASNs reserved for WKLCs is considered insignificant.
5. Security Considerations
The BGP Large Community Path attribute is transitive. Thus, a BGP
speaker that does not recognize the transitivity field may transmit
the WKLC contrary to the advisement of the transitivity field. If a
BGP speaker wishes not to receive any Large Community, it must
continue to filter it in the same way it was doing before the
transitivity field was introduced.
In some cases, a received route that contains an AS number from the
range assigned to WKLC in its AS_PATH may be considered unusual. A
receiving BGP speaker MAY drop such a received route in route-policy.
6. IANA Considerations
IANA is requested to assign the range 4093640704 (0xF4000000) to
4160749567 (0xF7FFFFFF) from the BGP ASN registry for BGP Well Known
Large Communities.
IANA is requested to create a registry of Well Known Large
Communities in the range 0 to 255. Numbers from this registry are to
be assigned in accordance with the policies defined in [RFC8126].
The policies for the following number ranges are:
0-63 - RFC Required
64-223 - First Come First Served
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224-255 - Experimental
7. 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>.
[RFC8092] Heitz, J., Ed., Snijders, J., Ed., Patel, K., Bagdonas,
I., and N. Hilliard, "BGP Large Communities Attribute",
RFC 8092, DOI 10.17487/RFC8092, February 2017,
<https://www.rfc-editor.org/info/rfc8092>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
Authors' Addresses
Jakob Heitz
Cisco
170 West Tasman Drive
San Jose, CA 95134
United States of America
Email: jheitz@cisco.com
Kotikalapudi Sriram
USA National Institute of Standards and Technology
100 Bureau Drive
Gaithersburg, MD 20899
United States of America
Email: kotikalapudi.sriram@nist.gov
Brian Dickson
Email: brian.peter.dickson@gmail.com
John Heasly
Email: heas@shrubbery.net
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