draft-ietf-idr-ext-opt-param-09.txt   draft-ietf-idr-ext-opt-param-10.txt 
Internet Engineering Task Force E. Chen Internet Engineering Task Force E. Chen
Internet-Draft Cisco Systems Internet-Draft Palo Alto Networks
Updates: 4271 (if approved) J. Scudder Updates: 4271 (if approved) J. Scudder
Intended status: Standards Track Juniper Networks Intended status: Standards Track Juniper Networks
Expires: February 22, 2021 August 21, 2020 Expires: September 23, 2021 March 22, 2021
Extended Optional Parameters Length for BGP OPEN Message Extended Optional Parameters Length for BGP OPEN Message
draft-ietf-idr-ext-opt-param-09 draft-ietf-idr-ext-opt-param-10
Abstract Abstract
The Optional Parameters in the BGP OPEN message as defined in the 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 base BGP specification are limited to 255 octets due to a one-octet
length field. BGP Capabilities are carried in this field and may length field. BGP Capabilities are carried in this field and may
foreseeably exceed 255 octets in the future, leading to concern about foreseeably exceed 255 octets in the future, leading to concern about
this limitation. this limitation.
In this document we update RFC 4271 by extending, in a backward- This document updates RFC 4271 by extending, in a backward-compatible
compatible manner, the length of the Optional Parameters in the BGP manner, the length of the Optional Parameters in the BGP OPEN. The
OPEN. The Parameter Length field of individual Optional Parameters Parameter Length field of individual Optional Parameters is also
is also extended. extended.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on February 22, 2021. This Internet-Draft will expire on September 23, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
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skipping to change at page 2, line 20 skipping to change at page 2, line 20
1. Introduction 1. Introduction
The Optional Parameters Length field in the BGP OPEN message is The Optional Parameters Length field in the BGP OPEN message is
defined in the base BGP specification [RFC4271] as one octet, thus defined in the base BGP specification [RFC4271] as one octet, thus
limiting the Optional Parameters field in the OPEN message to 255 limiting the Optional Parameters field in the OPEN message to 255
octets. Since BGP Capabilities [RFC5492] are carried in the Optional octets. Since BGP Capabilities [RFC5492] are carried in the Optional
Parameters field, and new BGP capabilities continue to be introduced, Parameters field, and new BGP capabilities continue to be introduced,
the limitation is a concern for BGP development. the limitation is a concern for BGP development.
In this document we update [RFC4271] by extending, in a backward- This document updates [RFC4271] by extending, in a backward-
compatible manner, the length of the Optional Parameters in BGP OPEN. compatible manner, the length of the Optional Parameters in BGP OPEN.
This is done by using Optional Parameter Type 255 as a distinguished This is done by using Optional Parameter Type 255 as a distinguished
value, that indicates an extended Optional Parameters Length field value, that indicates an extended Optional Parameters Length field
follows. In this case the Parameter Length field of the individual follows. In this case the Parameter Length field of the individual
Optional Parameters in the BGP OPEN message is also extended. Optional Parameters in the BGP OPEN message is also extended.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC 2119 [RFC2119]. "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. Protocol Extensions 2. Protocol Extensions
This document reserves Optional Parameter Type code 255 as the This document reserves Optional Parameter Type code 255 as the
"Extended Length" type code. "Extended Length" type code.
In the event that the length of Optional Parameters in the BGP OPEN In the event that the length of Optional Parameters in the BGP OPEN
message does not exceed 255, the encodings of the base BGP message does not exceed 255, the encodings of the base BGP
specification [RFC4271] MUST be used without alteration. However, an specification [RFC4271] MUST be used without alteration. However, an
implementation MUST be prepared to accept an OPEN message that uses implementation MUST be prepared to accept an OPEN message that uses
the encoding of this specification for Optional Parameters of any the encoding of this specification for Optional Parameters of any
length. length.
If the length of Optional Parameters is greater than 255, the However, if the length of Optional Parameters in the BGP OPEN message
extended encoding defined here MUST be used. The (non-extended) does exceed 255, the OPEN message MUST be encoded according to the
length field MUST be set to 255. The subsequent octet (which would procedure below.
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
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.
In this case, the BGP speaker MUST use the Extended Optional
Parameters Length field in lieu of the [RFC4271] encoding to
determine the length of Optional Parameters contained in the message.
Accordingly, when the length of Optional Parameters in the BGP OPEN
message is greater than 255, the OPEN message format is modified as
follows, using the first Optional Parameter Type field to indicate
the use of the extended format:
0 1 2 3 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 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 | | Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| My Autonomous System | | My Autonomous System |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hold Time | | Hold Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BGP Identifier | | BGP Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Non-Ext OP Len.|Non-Ext OP Type| Extended Opt. Parm. Length | |Non-Ext OP Len.|Non-Ext OP Type| Extended Opt. Parm. Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Optional Parameters (variable) | | Optional Parameters (variable) |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The non-extended Optional Parameters Length field MUST be set to 255 Figure 1: Extended Encoding OPEN Format
on transmission, 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 field.
The subsequent one-octet field, that in the non-extended format would The Non-Extended Optional Parameters Length field (Non-Ext OP Len)
be the first Optional Parameter Type field, MUST be set to 255 on SHOULD be set to 255 on transmission and in any event MUST NOT be set
transmission. On receipt, a value of 255 for this field is the to 0, and MUST be ignored on receipt once the use of the extended
indication that the extended format is in use. 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 In this extended encoding, the subsequent two-octet field, termed the
Extended Optional Parameters Length field, is an unsigned integer Extended Optional Parameters Length field, is an unsigned integer
indicating the total length of the Optional Parameters field in indicating the total length of the Optional Parameters field in
octets. If the value of this field is zero, no Optional Parameters octets. If the value of this field is zero, no Optional Parameters
are present. are present.
Likewise, in that situation the Optional Parameters encoding is Likewise, in that situation the Optional Parameters encoding is
modified to be the following: modified to be the following:
0 1 2 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 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 | | Parm. Type | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Parameter Value (variable) ~ ~ Parameter Value (variable) ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Extended Parameters Format
The rules for encoding Optional Parameters are unchanged with respect The rules for encoding Optional Parameters are unchanged with respect
to those given in [RFC4271] other than the extension of the Parameter to those given in [RFC4271] other than the extension of the Parameter
Length field to be a two-octet unsigned integer. Length field to be a two-octet unsigned integer.
In parsing an OPEN message, if the one-octet "Optional Parameters In parsing an OPEN message, if the one-octet "Optional Parameters
Length" field is non-zero, a BGP speaker MUST use the value of the Length" field is non-zero, a BGP speaker MUST use the value of the
octet following the one-octet "Optional Parameters Length" field to octet following the one-octet "Optional Parameters Length" field to
determine both the encoding of the Optional Parameters length and the determine both the encoding of the Optional Parameters length and the
size of the "Parameter Length" field of individual Optional size of the "Parameter Length" field of individual Optional
Parameters. If the value of this field is 255, then the encoding Parameters. If the value of this field is 255, then the encoding
described above is used for the Optional Parameters length. described above is used for the Optional Parameters length.
Otherwise the encoding defined in [RFC4271] is used. Otherwise the encoding defined in [RFC4271] is used.
This encoding is chosen for backward compatibility reasons -- a BGP
speaker which has not been upgraded to support this specification may
legitimately send Optional Parameters whose length equals exactly
255, thus the Optional Parameters Length field alone is insufficient
as an indicator. However, such a speaker would never legitimately
send an Optional Parameter whose type code is 255, since that value
has been reserved by this specification.
The choice to mandate that when the extended encoding is in use, the
(non-extended) Optional Parameters Length field must be 255 was made
for backward compatibility with implementations of earlier versions
of this specification. When the extended encoding is in use, the
value 0 MUST NOT be used in that field since the presence of that
value could have the effect of causing a message parser to never
inspect the following octet.
3. Errors 3. Errors
If a BGP speaker supporting this specification (a "new speaker") is If a BGP speaker supporting this specification (a "new speaker") is
peering with one which does not (an "old speaker") no peering with one which does not (an "old speaker") no
interoperability issues arise unless the new speaker needs to encode interoperability issues arise unless the new speaker needs to encode
Optional Parameters whose length exceeds 255. In that case, it will Optional Parameters whose length exceeds 255. In that case, it will
transmit an OPEN message which the old speaker will interpret as transmit an OPEN message which the old speaker will interpret as
containing an Optional Parameter with type code 255. Since by containing an Optional Parameter with type code 255. Since by
definition the old speaker will not recognize that type code, the old definition the old speaker will not recognize that type code, the old
speaker may be expected to close the connection with a NOTIFICATION speaker is expected to close the connection with a NOTIFICATION with
with an Error Code of OPEN Message Error and an Error Subcode of an Error Code of OPEN Message Error and an Error Subcode of
Unsupported Optional Parameters, according to Section 6.2 of Unsupported Optional Parameters, according to Section 6.2 of
[RFC4271]. [RFC4271].
Although the above is the most likely error to be sent, it is not
impossible that the old speaker might detect some other error first,
such as a length error, depending on the details of the
implementation. In no case would the peering be expected to
establish successfully; the only question is which NOTIFICATION would
be generated.
We note that in any case, such a peering could not succeed, since by
definition the extended length encoding would not be used by the new
speaker unless the basic encoding was insufficient.
Although the Optional Parameter Type code 255 is used in this Although the Optional Parameter Type code 255 is used in this
specification as the indication that the extended encoding is in use, specification as the indication that the extended encoding is in use,
it is not a bonafide Optional Parameter Type in the usual sense, and it is not a bonafide Optional Parameter Type in the usual sense, and
MUST NOT be used other than as described above. If encountered as an MUST NOT be used other than as described above. If encountered as an
actual Optional Parameter Type code, it MUST be treated as an actual Optional Parameter Type code, it MUST be treated as an
unrecognized Optional Parameter and handled according to [RFC4271] unrecognized Optional Parameter and handled according to [RFC4271]
Section 6.2. Section 6.2.
It is not considered an error to receive an OPEN message whose It is not considered an error to receive an OPEN message whose
Extended Optional Parameters Length value is less than or equal to Extended Optional Parameters Length value is less than or equal to
255, any value SHOULD be silently accepted. It is not considered a 255. It is not considered a fatal error to receive an OPEN message
fatal error to receive an OPEN message whose (non-extended) Optional whose (non-extended) Optional Parameters Length value is not 255, and
Parameters Length value is not 255, and whose first Optional whose first Optional Parameter type code is 255 -- in this case the
Parameter type code is 255 -- in this case the encoding of this encoding of this specification MUST be used for decoding the message.
specification MUST be used for decoding the message. A warning MAY A warning MAY be logged.
be logged.
4. IANA Considerations 4. IANA Considerations
IANA is requested to designate type code 255 in the BGP OPEN Optional IANA is requested to designate type code 255 in the BGP OPEN Optional
Parameter Types registry as the Extended Length type code. Parameter Types registry as the Extended Length type code.
5. Security Considerations 5. Security Considerations
This extension to BGP does not change the underlying security issues This extension to BGP does not change the underlying security or
inherent in the existing BGP [RFC4272]. confidentiality issues inherent in the existing BGP [RFC4272].
6. Acknowledgements 6. Acknowledgements
The authors would like to thank Yakov Rekhter and Srihari Sangli for The authors would like to thank Yakov Rekhter and Srihari Sangli for
discussing various options to enlarge the Optional Parameters field. discussing various options to enlarge the Optional Parameters field.
We would also like to thank Matthew Bocci, Bruno Decraene, John We would also like to thank Matthew Bocci, Bruno Decraene, John
Heasley, Jakob Heitz, Pradosh Mohapatra, Keyur Patel and Hannes Heasley, Jakob Heitz, Pradosh Mohapatra, Keyur Patel and Hannes
Gredler for their valuable comments. Gredler for their valuable comments.
7. References 7. References
skipping to change at page 6, line 27 skipping to change at page 5, line 42
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006, DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>. <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 7.2. Informative References
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006, RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>. <https://www.rfc-editor.org/info/rfc4272>.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <https://www.rfc-editor.org/info/rfc5492>. 2009, <https://www.rfc-editor.org/info/rfc5492>.
Authors' Addresses Authors' Addresses
Enke Chen Enke Chen
Cisco Systems Palo Alto Networks
Email: enkechen@cisco.com Email: enchen@paloaltonetworks.com
John Scudder John Scudder
Juniper Networks Juniper Networks
Email: jgs@juniper.net Email: jgs@juniper.net
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