Internet DRAFT - draft-ietf-idr-ext-opt-param
draft-ietf-idr-ext-opt-param
IDR E. Chen
Internet-Draft Palo Alto Networks
Updates: 4271 (if approved) J. Scudder
Intended status: Standards Track Juniper Networks
Expires: October 24, 2021 April 22, 2021
Extended Optional Parameters Length for BGP OPEN Message
draft-ietf-idr-ext-opt-param-13
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.
This document updates RFC 4271 by extending, in a backward-compatible
manner, the length of the Optional Parameters in the BGP OPEN. 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 October 24, 2021.
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
Chen & Scudder Expires October 24, 2021 [Page 1]
Internet-Draft Extended Optional Parameters Length April 2021
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.
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.
This document updates [RFC4271] by extending, in a backward-
compatible manner, the length of the Optional Parameters in BGP OPEN.
This is done by using Optional Parameter Type 255 as a distinguished
value, that indicates an extended Optional Parameters Length field
follows and that the parsing of the BGP OPEN should be modified
according to these procedures. In this case the Parameter Length
field of the individual 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", "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. Update to RFC 4271
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] SHOULD be used without alteration.
Configuration MAY override this to force the extended format to be
used in all cases; this might be used, for example to test that a
peer supports this specification. (In any case, an implementation
MUST accept an OPEN message that uses the encoding of this
specification even if the length of Optional Parameters is 255 or
less.)
Chen & Scudder Expires October 24, 2021 [Page 2]
Internet-Draft Extended Optional Parameters Length April 2021
However, if the length of Optional Parameters in the BGP OPEN message
does exceed 255, the OPEN message MUST be encoded according to the
procedure below.
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
+-+-+-+-+-+-+-+-+
| Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| My Autonomous System |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hold Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BGP Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Non-Ext OP Len.|Non-Ext OP Type| Extended Opt. Parm. Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Optional Parameters (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended Encoding OPEN Format
The Non-Extended Optional Parameters Length field (Non-Ext OP Len)
SHOULD be set to 255 on transmission and in any event MUST NOT be set
to 0, and MUST be ignored on receipt once the use of the extended
format is determined positively by inspection of the Non-Extended
Optional Parameters Type (Non-Ext OP Type) field.
The subsequent one-octet field (that would be the first Optional
Parameter Type field in the non-extended format, and is called "Non-
Ext OP Type" in the figure above) MUST be set to 255 on transmission.
On receipt, a value of 255 for this field is the indication that the
extended format is in use.
In this extended encoding, the subsequent two-octet field, termed the
Extended Optional Parameters Length field, is an unsigned integer
indicating the total length of the Optional Parameters field in
octets. If the value of this field is zero, no Optional Parameters
are present.
Likewise, in that situation the Optional Parameters encoding is
modified to be the following:
Chen & Scudder Expires October 24, 2021 [Page 3]
Internet-Draft Extended Optional Parameters Length April 2021
0 1 2
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parm. Type | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Parameter Value (variable) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Extended Parameters Format
The rules for encoding Optional Parameters are unchanged with respect
to those given in [RFC4271] other than the extension of the Parameter
Length field to be a two-octet unsigned integer.
In parsing an OPEN message, if the one-octet "Optional Parameters
Length" field (labeled "Non-Ext OP Len." in Figure 1) is non-zero, a
BGP speaker MUST use the value of the octet following the one-octet
"Optional Parameters Length" field (labeled "Non-Ext OP Type" in
Figure 1) to determine both the encoding of the Optional Parameters
length and the size of the "Parameter Length" field of individual
Optional Parameters. If the value of the "Non-Ext OP Type" field is
255, then the encoding described above is used for the Optional
Parameters length. Otherwise the encoding defined in [RFC4271] is
used.
3. Backward Compatibility
If a BGP speaker supporting this specification (a "new speaker") is
peering with one which does not (an "old speaker") no
interoperability issues arise unless the new speaker needs to encode
Optional Parameters whose length exceeds 255. In that case, it will
transmit an OPEN message which the old speaker will interpret as
containing an Optional Parameter with type code 255. Since by
definition the old speaker will not recognize that type code, the old
speaker is expected to close the connection with a NOTIFICATION with
an Error Code of OPEN Message Error and an Error Subcode of
Unsupported Optional Parameters, according to Section 6.2 of
[RFC4271].
Although the Optional Parameter Type code 255 is used in this
specification as the indication that the extended encoding is in use,
it is not a bona fide Optional Parameter Type in the usual sense, and
MUST NOT be used other than as described above. If encountered in
any position other than the first Optional Parameter Type, it MUST be
treated as an unrecognized Optional Parameter and handled according
to [RFC4271] Section 6.2.
Chen & Scudder Expires October 24, 2021 [Page 4]
Internet-Draft Extended Optional Parameters Length April 2021
It is not considered an error to receive an OPEN message whose
Extended Optional Parameters Length value is less than or equal to
255. It is not considered a fatal error to receive an OPEN message
whose (non-extended) Optional Parameters Length value is not 255, and
whose first Optional Parameter type code is 255 -- in this case the
encoding of this specification MUST be used for decoding the message.
4. IANA Considerations
IANA is requested to designate type code 255 in the BGP OPEN Optional
Parameter Types registry as the Extended Length type code.
5. Security Considerations
This extension to BGP does not change the underlying security or
confidentiality issues inherent in the existing BGP [RFC4272].
6. Acknowledgements
The authors would like to thank Yakov Rekhter and Srihari Sangli for
discussing various options to enlarge the Optional Parameters field.
We would also like to thank Matthew Bocci, Bruno Decraene, John
Heasley, Jakob Heitz, Christer Holmberg, Pradosh Mohapatra, Keyur
Patel and Hannes Gredler for their valuable comments.
7. References
7.1. 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>.
[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>.
[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>.
7.2. Informative References
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>.
Chen & Scudder Expires October 24, 2021 [Page 5]
Internet-Draft Extended Optional Parameters Length April 2021
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <https://www.rfc-editor.org/info/rfc5492>.
Authors' Addresses
Enke Chen
Palo Alto Networks
Email: enchen@paloaltonetworks.com
John Scudder
Juniper Networks
Email: jgs@juniper.net
Chen & Scudder Expires October 24, 2021 [Page 6]
