Extended Optional Parameters Length for BGP OPEN Message
draft-ietf-idr-ext-opt-param-07
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(latest revision 2019-08-01)
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draft-chen-bgp-ext-opt-param
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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
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 1, 2020.
Copyright Notice
Copyright (c) 2019 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
Chen & Scudder Expires February 1, 2020 [Page 1]
Internet-Draft Extended Optional Parameters Length July 2019
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.
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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Internet-Draft Extended Optional Parameters Length July 2019
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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