LSR Working Group P. Kaneriya
Internet-Draft Tony. Li
Intended status: Standards Track Antoni. Przygienda
Expires: 25 July 2022 S. Hegde
C. Bowers
Juniper Networks
L. Ginsberg
Cisco Systems
21 January 2022
Multiple TLV Instances in IS-IS
draft-pkaneria-lsr-multi-tlv-00
Abstract
Emerging technologies are adding information into IS-IS TLVs at a
steady pace while deployment scales are simultaneously increasing.
This causes the contents of many critical TLVs to exceed the
currently supported limit of 255 octets. Extensions such as
[RFC7356] require significant IS-IS changes that could help address
the problem, but a less drastic solution would be beneficial. This
document codifies the common mechanism of extending the TLV space
through multiple TLV instances.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 25 July 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Procedure for Advertising Multiple TLV Instances . . . . . . 3
4. Procedure for Receiving Multiple TLV Instances . . . . . . . 4
5. Operational Considerations . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The continued growth of the Internet has resulted in a commensurate
growth in the scale of service provider networks and the amount of
information carried in IS-IS [ISO10589] Type-Length-Value (TLV)
tuples. Simultaneously, new traffic engineering technologies are
defining new attributes, further adding to the scaling pressures.
The original TLV definition allows for 255 octets of payload, which
is becoming increasingly inadequate.
Some TLV definitions have addressed this by explicitly stating that a
TLV may appear multiple times inside of an LSP. However, this has
not been done for many legacy TLVs, leaving the situation ambiguous.
The intent of this document is to clarify the situation by explicitly
defining the use of multiple instances of TLVs as the mechanism for
scaling TLV contents, except where explicitly prohibited.
Today, as an example, the Extended IS Reachability TLV (22) [RFC5305]
and MT Intermediate Systems TLV (222) [RFC5120] are TLVs where
existing standards do not specify the behavior expected when multiple
copies of the TLV are present and no other mechanism for expanding
the information carrying capacity of the TLV has been specified.
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[RFC7356] has proposed a 16 bit length field for TLVs in flooding
scoped Protocol Data Units (PDUs), but does nothing to address legacy
implementations that do not yet implement the full breadth and scope
of that RFC.
2. 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.
3. Procedure for Advertising Multiple TLV Instances
If the TLV contains information that specifies the applicability of
its contents (i.e., a key), the key information MUST be replicated in
additional TLV instances so that all contents specific to that key
can be identified. This allows more sub-TLVs to be advertised for
the same key information. The specification of the key for a given
TLV is out of scope for this document.
This should be applied recursively. If a TLV is structured with sub-
TLVs and sub-sub-TLVs, then replication of key information allows for
the advertisement of additional sub-TLVs and sub-sub-TLVs for that
key.
Note: If the fixed portion of a TLV includes information that is NOT
part of the key and the non-key elements of the fixed portion of the
TLV (metric and other bits in the control octet in the example below)
differ, the values in the first TLV present in the lowest numbered
LSP MUST be used.
As an example, consider the Extended IP Reachability TLV (type 135).
A prefix in this TLV is specified by:
* 4 octets of metric information
* 1 octet of control information which includes 6 bits specifying
the prefix length
* 0-4 octets of IPv4 prefix
followed by up to 250 octets of sub-TLV information.
The key consists of the 6 bits of prefix length and the 0-4 octets of
IPv4 prefix.
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If this is insufficient sub-TLV space, then the node MAY advertise
additional instances of the Extended IS Reachability TLV. The key
information MUST be replicated identically and the additional sub-TLV
space may be populated with additional information. The complete
information for a given key in such cases is the joined set of all
the carried information under the key in all the TLV instances.
4. Procedure for Receiving Multiple TLV Instances
A node that receives multiple TLV instances MUST accept all of the
information in all of the instances. The order of arrival and
placement of the TLV instances in LSP fragments MUST NOT change the
behavior of the node once all the fragments have been received.
The contents of multiple TLV instances of the same type should be
processed as if they were concatenated. If the internals of the TLV
contain key information, then replication of the key information
should be taken to indicate that subsequent data should be processed
as if the subsequent data were concatenated.
Specifically, if a TLV is structured with sub-TLVs and key
information is replicated, then the sub-TLVs should be processed as
if they were concatenated.
This process should be applied recursively. If a TLV is structured
with sub-TLVs and sub-sub-TLVs with replicated key information at all
levels, then sub-sub-TLVs should be processed as if they were
concatenated.
For example, suppose that a node received an LSP with multiple
instances of the Extended IS Reachability TLV. The first instance
contained key information K with sub-TLVs A, B, and C. The second
instance contained key information K with sub-TLVs D, E, and F. The
receiving node should then process this as having key information K
and sub-TLVs A, B, C, D, E, F, or, because ordering is irrelevant,
sub-TLVs D, E, F, A, B, C.
5. Operational Considerations
The generation of multiple TLVs for a given object is triggered by
more information than will fit into a single TLV. If multiple TLVs
are advertised in the presence of nodes which do not support multiple
TLVs, operation of routing in the network is likely to be
compromised.
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6. IANA Considerations
This document makes no requests of IANA.
7. Security Considerations
This document creates no new security issues for IS-IS. Additional
instances of existing TLVs expose no new information.
Security concerns for IS-IS are addressed in [ISO10589], [RFC5304],
and [RFC5310].
8. References
8.1. Normative References
[ISO10589] ISO, "Intermediate system to Intermediate system routing
information exchange protocol for use in conjunction with
the Protocol for providing the Connectionless-mode Network
Service (ISO 8473)", August 1987, <ISO/IEC 10589:2002>.
[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>.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304, October
2008, <https://www.rfc-editor.org/info/rfc5304>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310, February
2009, <https://www.rfc-editor.org/info/rfc5310>.
[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>.
8.2. Informative References
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
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[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
Scope Link State PDUs (LSPs)", RFC 7356,
DOI 10.17487/RFC7356, September 2014,
<https://www.rfc-editor.org/info/rfc7356>.
Authors' Addresses
Parag Kaneriya
Juniper Networks
Elnath-Exora Business Park Survey
Bangalore 560103
Karnataka
India
Email: pkaneria@juniper.net
Tony Li,
Juniper Networks
1133 Innovation Way
Sunnyvale, California 94089
United States of America
Email: tony.li@tony.li
Antoni Przygienda,
Juniper Networks
1133 Innovation Way
Sunnyvale, California 94089
United States of America
Email: prz@juniper.net
Shraddha Hegde
Juniper Networks
Elnath-Exora Business Park Survey
Bangalore 560103
Karnataka
India
Email: shraddha@juniper.net
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Chris Bowers
Juniper Networks
1133 Innovation Way
Sunnyvale, California 94089
United States of America
Email: cbower@juniper.net
Les Ginsberg
Cisco Systems
821 Alder Drive
Milpitas, CA 95035
United States of America
Email: ginsberg@cisco.com
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