IGP extensions for Advertising Offset for Flex-Algorithm
draft-chan-lsr-igp-adv-offset-00
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| Authors | Louis Chan , Krzysztof Grzegorz Szarkowicz | ||
| Last updated | 2022-03-07 | ||
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draft-chan-lsr-igp-adv-offset-00
LSR Working Group Louis Chan
INTERNET-DRAFT Krzysztof Szarkowicz
Intended status: Standard Track Juniper Networks
Expires: Sep 6, 2022 Mar 6, 2022
IGP extensions for Advertising Offset for Flex-Algorithm
draft-chan-lsr-igp-adv-offset-00.txt
Abstract
This document describes the IGP extensions to provide predictable Adjacency-SIDs
per Flex-Algorithm [FLEXALGO] in segment routing.
We propose some methods to allow the advertisement of additional TLV in IGP so that
the Flex-Algorithm specific Adjacency-SIDs could be automatically derived.
With the proposed method, the size of advertisement on per node per link basis is
greatly reduced. Each participating router would derive the required labels
automatically.
Extensions for offset to derive Flex-Algorithm Prefix-SID is also included in the
document.
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-
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inappropriate to use Internet-Drafts as reference material or to cite them other
than as "work in progress."
This Internet-Draft will expire on Sep 6, 2022.
Copyright Notice
Copyright (c) 2017 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
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Components extracted from this document must include Simplified BSD License text as
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described in Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction...................................................2
2. Conventions used in this document..............................2
3. ISIS extension.................................................2
3.1. Algorithm Offset for Adj-SID..............................3
3.2. Algorithm Offset for LAN based Adj-SID....................4
3.3. Algorithm Offset for Prefix SID...........................5
4. Compatibility..................................................6
5. OSPF extension.................................................6
6. Security Consideration.........................................6
7. References.....................................................7
7.1. Normative References......................................7
7.2. Informative References....................................7
8. Acknowledgments................................................7
1. Introduction
The draft proposes methods for routers to announce Flex-Algorithm specific
Adjacency-SID with minimal advertisement in IGP. When the other routers need a SR
policy (aka SR-TE) or TI-LFA path, the Flex-Algorithm specific Adjacency-SID would
be taken into the path label construction.
Hence, the top most label, either node or link related, in a SR policy stack would
be used to identify a certain Flex-Algo with full identification.
2. Conventions used in this document
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].
In this document, these words will appear with that interpretation only when in ALL
CAPS. Lower case uses of these words are not to be interpreted as carrying
significance described in RFC 2119.
3. ISIS extension
With reference to RFC8667, the information could be advertised in SR-Capabilities
sub-TLV in Section 3.
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3.1. Algorithm Offset for Adj-SID
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label | Base offset/Index offset (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Flags/ Algo/ Base offset/ Index offset ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TDB
Length: variable; multiple advertisements
Flags: 1 octet field of the following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| |B|V|L| |
+-+-+-+-+-+-+-+-+
where:
B-Flag: Backup Flag. If set, the Adj-SID is eligible
for protection (e.g., using IP Fast Reroute
(IPFRR) or MPLS Fast Reroute (MPLS-FRR)) as
described in [RFC8402].
V-Flag: Value Flag. If set, then it carries
a label value. If not set, it is an index value.
L-Flag: Local Flag. Always set to 1
Algorithm: 1 octet
Flex-Algo value is between 128 and 255.
Base Offset: 3 octets
Local label base for Adjacency-SIDs for given Flex-
Algorithm. The derived Adjacency-SID is the sum of the base
offset and the Algo 0 label
Index Offset: 4 octets
If Adjacency-SID is advertised as index, this provides an
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offset index value. The new label is sum of (SRGB base +
index + index offset)
The format of Base Offset and Index Offset is the same as RFC8667. The choice of
advertising Base Offset or Index Offset must match the advertisement of original
Adjacency-SID method from the same router.
3.2. Algorithm Offset for LAN based Adj-SID
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor System-ID (ID length octets) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label Base Offset/Index Offset (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Flags/ Algo/NB Sys-ID/ SID/Label/Index Offset (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TDB
Length: variable; multiple advertisements
Flags: 1 octet field of the following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| |B|V|L| |
+-+-+-+-+-+-+-+-+
where:
B-Flag: Backup Flag. If set, the Adj-SID is eligible
for protection (e.g., using IP Fast Reroute
(IPFRR) or MPLS Fast Reroute (MPLS-FRR)) as
described in [RFC8402].
V-Flag: Value Flag. If set, then it carries
a label value. If not set, it is an index value.
L-Flag: Local Flag. Always set to 1
Algorithm: 1 octet. Same as Section 5.1
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Neighbor System-ID: IS-IS System-ID of length "ID Length" as
defined in [ISO10589].
Base Offset: 3 octets. Same as Section 5.1
Index Offset: 4 octets. Same as Section 5.1
3.3. Algorithm Offset for Prefix SID
Prefix-SID for Algorithm could also be generated by adding an index offset value or
a base offset for label.
This advertisement is an sub-TLV in RFC8667 Section 2.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label Base offset/ Index offset ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Flags/ Algorithm/ Base Offset/ Index offset ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: TDB
Length: variable
Flags: 1 octet field of the following flags:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|R|N| |V|L| |
+-+-+-+-+-+-+-+-+
where:
R-Flag: Re-advertisement Flag. If set, then the prefix
to which this Prefix-SID is attached has been
propagated by the router from either another
level (i.e., from Level-1 to Level-2 or the
opposite) or redistribution (e.g., from another
protocol).
N-Flag: Node-SID Flag. If set, then the Prefix-SID
refers to the router identified by the prefix.
Typically, the N-Flag is set on Prefix-SIDs that
are attached to a router loopback address. The
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N-Flag is set when the Prefix-SID is a Node-SID
as described in [RFC8402].
V-Flag: Value Flag. If set, then it carries
a label value. If not set, it is an index value.
L-Flag: Local Flag. Always set to 0
Algorithm: 1 octet
Flex-Algo value is between 128 and 255
Base offset: 3 octets
Label base for Prefix-SIDs for given Algorithm
The derived Prefix-SID is the sum of the base
Offset and the Algo 0 label
Index Offset: 4 octets
Index offset counting from Algo 0
The new label for Prefix is sum of (SRGB base +
index + index offset)
The format of Base offset and Index Offset is the same as RFC8667. The choice of
advertising Base Offset or Index Offset MUST match the advertisement of original
Prefix-SID method from the same router.
4. Compatibility
For nodes that do not support Algorithm Offset for Adj-SID extension, the label
stack could use normal Adj-SID, providing that the node still supports Flex-Algo
Prefix SID.
For TI-LFA, there would be two modes of operation - loose or strict. For strict
mode, all Adj-SID involved in TI-LFA candidate path must be derived with offset
method.
For loose mode, Adj-SID in the TI-LFA candidate path could be a mix of Adj-SID's
with and without offset. This allows backward compatibility with routers which only
support Flex-Algo.
5. OSPF extension
TBD
6. Security Consideration
TBD
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels",
BCP 14, RFC 2119, March 1997.
7.2. Informative References
[RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
Extensions for Segment Routing", RFC 8667,
DOI 10.17487/RFC8667, December 2019,
<https://www.rfc-editor.org/info/rfc8667>.
[TI-LFA] Litkowski, S., Bashandy, A., Filsfils, C., Francois, P.,
Decraene, B., and D. Voyer, "Topology Independent Fast
Reroute using Segment Routing",
<https://datatracker.ietf.org/doc/html/draft-ietf-rtgwg-segment-
routing-ti-lfa>
[FLEXAGLO] S. Hegde, P. Psenak and etc, IGP Flexible Algorithm
https://datatracker.ietf.org/doc/draft-ietf-lsr-flex-algo
[ISO10589] International Organization for Standardization,
"Information technology -- Telecommunications and
information exchange between systems -- Intermediate
system to Intermediate system intra-domain routeing
information exchange protocol for use in conjunction with
the protocol for providing the connectionless-mode network
service (ISO 8473)", ISO/IEC 10589:2002, Second Edition,
November 2002.
8. Acknowledgments
The following people have contributed to this document:
Shraddha Hegde, Juniper Networks
Author Address
Louis Chan
Juniper Networks
2604, Cityplaza One, 1111 King's Road
Taikoo Shing
Hong Kong
Phone: +852-25876659
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Email: louisc@juniper.net
Krzysztof Grzegorz Szarkowicz
Juniper Networks
Parkring 10
A-1010 Wien
Austria
Phone: +49 89 203012127
Email: kszarkowicz@juniper.net
Chan Expires Sep 6, 2022 [Page 8]