Extended Optional Parameters Length for BGP OPEN Message
draft-ietf-idr-ext-opt-param-07
Internet Engineering Task Force E. Chen
Internet-Draft Cisco Systems
Updates: 4271 (if approved) J. Scudder
Intended status: Standards Track Juniper Networks
Expires: February 1, 2020 July 31, 2019
Extended Optional Parameters Length for BGP OPEN Message
draft-ietf-idr-ext-opt-param-07
Abstract
The Optional Parameters in the BGP OPEN message as defined in the
base BGP specification are limited to 255 octets due to a one-octet
length field. BGP Capabilities are carried in this field and may
foreseeably exceed 255 octets in the future, leading to concern about
this limitation.
In this document we update RFC 4271 by extending the BGP OPEN length
field in a backward-compatible manner. The Parameter Length field of
individual Optional Parameters is also extended.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on February 1, 2020.
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1. Introduction
The Optional Parameters Length field in the BGP OPEN message is
defined in the base BGP specification [RFC4271] as one octet, thus
limiting the Optional Parameters field in the OPEN message to 255
octets. Since BGP Capabilities [RFC5492] are carried in the Optional
Parameters field, and new BGP capabilities continue to be introduced,
the limitation is a concern for BGP development.
In this document we update [RFC4271] by extending the BGP OPEN length
field in a backward-compatible manner. The Parameter Length field of
individual Optional Parameters is also extended. This is done by
using Optional Parameter Type 255 as a distinguished value, that
indicates an extended Optional Parameters Length field follows. In
this case the Parameter Length field of the Optional Parameters in
the BGP OPEN message is also extended.
1.1. 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 RFC 2119 [RFC2119].
2. Protocol Extensions
This document reserves Optional Parameter Type code 255 as the
"Extended Length" type code.
In the event that the length of Optional Parameters in the BGP OPEN
message does not exceed 255, the encodings of the base BGP
specification [RFC4271] MUST be used without alteration. However, an
implementation MUST be prepared to accept an OPEN message that uses
the encoding of this specification for Optional Parameters of any
length.
If the length of Optional Parameters is greater than 255, the
extended encoding defined here MUST be used. The (non-extended)
length field MUST be set to 255. The subsequent octet (which would
be the first Optional Parameter Type in the non-extended format) MUST
be set to 255 as well. The subsequent two octets carry the actual
length. In addition, the "Parameter Length" field of each Optional
Parameter is enlarged to two octets. Other than the larger sizes of
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the given fields, there is no change to the BGP OPEN message defined
in [RFC4271].
When receiving an OPEN, a BGP speaker determines the extended
encoding is in use if the first Optional Parameter Type field is 255.
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