IS-IS Extensions To Support The IPv6 Compressed Routing Header (CRH)
draft-bonica-lsr-crh-isis-extensions-01

Abstract

Source nodes can use the IPv6 Compressed Routing Header (CRH) to steer packets through a specified path. This document defines IS-IS extensions that support the CRH.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on May 7, 2020.

Copyright Notice

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1. Introduction
2. Requirements Language
3. Advertising The CRH Capability
4. Advertising Supported Algorithms
5. Advertising Loosely Routed Segment Identifiers
6. Advertising Strictly Routed Segment Identifiers
7. Advertising Strictly Routed Segment Identifiers Into LANs
8. IANA Considerations

8.1. The CRH Sub-TLV
8.2. Loosely Routed SID Sub-TLV
8.3. Strictly Routed SID Sub-TLV

9. Security Considerations
10. Acknowledgements
11. References

11.1. Normative References
11.2. Informative References

Authors' Addresses

1. Introduction

Source nodes can use the IPv6 Compressed Routing Header (CRH) to steer packets through a specified path. This document defines IS-IS extensions that support the CRH.

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 [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Advertising The CRH Capability

The Router CAPABILITY TLV MAY contain exactly one CRH sub-TLV. The CRH sub-TLV indicates that the advertising node can process the CRH.

The CRH sub-TLV MAY contain sub-sub-TLVs. No sub-sub-TLVs are currently defined.

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     |  Max CRH Len  |    Reserved   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: CRH Sub-TLV

Figure 1 depicts the CRH sub-TLV. The CRH sub-TLV contains the following fields:

Type: 8 bits. CRH (value TBD by IANA)
Length: 8 bits. Length of TLV data excluding the TLV header. MUST be equal to 2 plus the length of sub-sub-TLVs (if any).
Max CRH Len: 8 bits. Maximum CRH length supported by the advertising node, measured in 8-octet units, not including the first 8 octets. See Note 1.
Reserved: 8 bits. SHOULD be set to zero by sender. MUST be ignored by receiver.

Note 1: According to [RFC8200], all IPv6 Routings header include a "Hdr Ext Len" field. That field specifies the length of the Routing header in 8-octet units, not including the first 8 octets. The same unit of measure was chosen for the "Max CRH Len" field in the CRH sub-TLV.

4. Advertising Supported Algorithms

CRH-capable nodes use the SR Algorithm TLV [I-D.ietf-isis-segment-routing-extensions] to specify the algorithms that they support.

5. Advertising Loosely Routed Segment Identifiers

The following TLVs MAY contain one or more Loosely Routed SID sub-TLVs:

[I-D.bonica-6man-comp-rtg-hdr].

TLV-236 (IPv6 IP Reachability) [RFC5308].
TLV-237 (Multitopology IPv6 IP Reachability) [RFC5120].

The Loosely Routed SID sub-TLV is valid only when its parent TLV specifies a prefix length of 128. In this case, it binds the SID that it contains to the prefix (i.e., IPv6 address) that its parent TLV contains. This information is used to construct the mapping table described in

When the parent TLV is propagated across level boundaries, the Loosely Routed SID sub-TLV SHOULD be kept.

    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    |    Reserved   |   Algorithm   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            SID         
   +-+-+-+-+-+-+-+

Figure 2: Loosely Routed SID sub-TLV

Figure 2 depicts the Loosely Routed SID sub-TLV. It contains the following fields:

Type: 8 bits. Loosely Routed SID sub-TLV (Value TBD by IANA)
Length: 8 bits. Length of TLV data excluding the TLV header, measured in bytes.
Reserved: SHOULD be set to zero by the sender. MUST be ignored by the receiver.
Algorithm : 8 bits. The router may use various algorithms when calculating reachability to other nodes. Algorithms identifiers are defined in Section 3.2 of [I-D.ietf-isis-segment-routing-extensions].
SID - Variable length. Segment Identifier.

6. Advertising Strictly Routed Segment Identifiers

The following TLVs can contain one or more Strictly Routed SID sub-TLVs:

TLV-22 (Extended IS reachability) [RFC5305]
TLV-222 (Multitopology IS) [RFC5120]
TLV-23 (IS Neighbor Attribute) [RFC5311]
TLV-223 (Multitopology IS Neighbor Attribute) [RFC5311]
TLV-141 (inter-AS reachability information) [RFC5316]

The Strictly Routed SID sub-TLV is valid only when its parent TLV also contains an IPv6 Neighbor Address sub-TLVs. In this case, the SID contained by the Strictly Routed SID sub-TLV is bound to the IPv6 address contained by the IPv6 Neighbor Address sub-TLV. This information is used to construct the mapping table described in [I-D.bonica-6man-comp-rtg-hdr].

    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     |     Weight    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            SID            
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Figure 3: Strictly Routed SID Sub-TLV

Figure 3 depicts the Strictly Routed SID sub-TLV. It contains the following fields:

Type: 8 bits. Strictly Routed SID sub-TLV (Value TBD by IANA)
Length: 8 bits. Length of TLV data excluding the TLV header, measured in bytes.
Flags: 8 bits. See below.
Weight: 8 bits. The value represents the SID weight for the purpose of load balancing. The use of the weight is defined in [RFC8402].
SID - Variable length. Segment Identifier.

          0 1 2 3 4 5 6 7
         +-+-+-+-+-+-+-+-+
         |B|S|P| Reserved|
         +-+-+-+-+-+-+-+-+

Figure 4: Strictly Routed SID Sub-TLV Flags

Figure 4 depicts Strictly Routed SID Sub-TLV flags. They include the following:

B-Flag: Backup flag. If set, the SID is eligible for protection as described in [RFC8402].
S-Flag:. Set flag. When set, the S-Flag indicates that the SID refers to a set of adjacencies (and therefore MAY be assigned to other adjacencies as well).
P-Flag: Persistent flag. When set, the P-Flag indicates that the SID is persistently allocated, i.e., the SID value remains consistent across router restart and/or interface flap.)

7. Advertising Strictly Routed Segment Identifiers Into LANs

In LAN subnetworks, the Designated Intermediate System (DIS) is elected and originates the Pseudonode-LSP (PN-LSP) including all neighbors of the DIS.

When the CRH is used, each router in the LAN MAY advertise its Strictly Routed SIDs of each of its neighbors. Since, on LANs, each router only advertises one adjacency to the DIS (and doesn't advertise any other adjacency), each router advertises the set of Strictly routed SIDs (for each of its neighbors) inside a newly defined sub-TLV part of the TLV advertising the adjacency to the DIS (e.g.: TLV-22).

The following TLVs can contain one or more LAN Strictly Routed SID sub-TLVs:

TLV-22 (Extended IS reachability) [RFC5305]
TLV-222 (Multitopology IS) [RFC5120]
TLV-23 (IS Neighbor Attribute) [RFC5311]
TLV-223 (Multitopology IS Neighbor Attribute) [RFC5311]

The LAN Strictly Routed SID sub-TLV binds an IPv6 address to a SID. The sub-TLV contains both the IPv6 address and the SID. This information is used to construct the mapping table described in [I-D.bonica-6man-comp-rtg-hdr].

    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    |    Weight     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Neighbor System-ID (ID length octets)        |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            SID            
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Figure 5: LAN Strictly Routed SID Sub-TLV

Figure 5 depicts the Strictly Routed SID sub-TLV. It contains the following fields:

Type: 8 bits. Strictly Routed SID sub-TLV (Value TBD by IANA)
Length: 8 bits. Length of TLV data excluding the TLV header, measured in bytes.
Flags: 8 bits. See below.
Weight: 8 bits. The value represents the SID weight for the purpose of load balancing. The use of the weight is defined in [RFC8402].
Neighbor System-ID: 6 bytes. IS-IS System-ID of length "ID Length" as defined in [ISO10589].
SID - Variable length. Segment Identifier.

          0 1 2 3 4 5 6 7
         +-+-+-+-+-+-+-+-+
         |B|S|P| Reserved|
         +-+-+-+-+-+-+-+-+

Figure 6: Strictly Routed SID Sub-TLV Flags

Figure 6 depicts Strictly Routed SID Sub-TLV flags. They include the following:

B-Flag: Backup flag. If set, the SID is eligible for protection as described in [RFC8402].
S-Flag:. Set flag. When set, the S-Flag indicates that the SID refers to a set of adjacencies (and therefore MAY be assigned to other adjacencies as well).
P-Flag: Persistent flag. When set, the P-Flag indicates that the SID is persistently allocated, i.e., the SID value remains consistent across router restart and/or interface flap.)

8. IANA Considerations

8.1. The CRH Sub-TLV

IANA is requested to add a new sub-TLV in the Sub-TLVs for TLV 242 (IS-IS Router CAPABILITY TLV) Registry.

[RFC7370]. Suggested registry name is "sub-sub-TLVs for CRH sub-TLV". No sub- sub-TLVs are defined by this document except for the reserved value.

Value - TBD by IANA
Description - CRH include

This document requests the creation of a new IANA managed registry for sub-sub-TLVs of the CRH sub-TLV. The registration procedure is "Expert Review" as defined in

0 - Reserved
1 - 255 Unassigned

8.2. Loosely Routed SID Sub-TLV

IANA is requested to add a new entry in the Sub-TLVs for TLVs 135, 235, 236, and 237 (Extended IP reachability, MT IP. Reach, IPv6 IP. Reach, and MT IPv6 IP. Reach TLVs) Registry.

Value - TBD by IANA
Description - Loosely Routed SID
135 - N
136 - N
236 - Y
237 - Y
Reference - This document.

8.3. Strictly Routed SID Sub-TLV

IANA is requested to add the following entries in the Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223 (Extended IS reachability, IS Neighbor Attribute, L2 Bundle Member Attributes, inter-AS reachability information, MT-ISN, and MT IS Neighbor Attribute TLVs) Registry.

The first entry follows:

Value - TBD by IANA
Description - Strictly Routed SID
22 - Y
23 - Y
25 - N
141 - Y
222 - Y
223 - Y
Reference - This document.

The second entry follows:

Value - TBD by IANA
Description - LAN Strictly Routed SID
22 - Y
23 - Y
25 - N
141 - N
222 - Y
223 - Y
Reference - This document.

9. Security Considerations

Security concerns for IS-IS are addressed in [ISO10589], [RFC5304], and [RFC5310].

10. Acknowledgements

Thanks to Ram Santhanakrishnan for his comments on this document.

11. References

11.1. Normative References

[I-D.bonica-6man-comp-rtg-hdr]	Bonica, R., Kamite, Y., Niwa, T., Alston, A., Henriques, D., Jalil, L., So, N., Xu, F., Chen, G., Zhu, Y., Yang, G. and Y. Zhou, "The IPv6 Compressed Routing Header (CRH)", Internet-Draft draft-bonica-6man-comp-rtg-hdr-08, October 2019.
[I-D.ietf-isis-segment-routing-extensions]	Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., Gredler, H. and B. Decraene, "IS-IS Extensions for Segment Routing", Internet-Draft draft-ietf-isis-segment-routing-extensions-25, May 2019.
[ISO10589]	, "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.
[RFC2119]	Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[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.
[RFC5304]	Li, T. and R. Atkinson, "IS-IS Cryptographic Authentication", RFC 5304, DOI 10.17487/RFC5304, October 2008.
[RFC5305]	Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2008.
[RFC5308]	Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, DOI 10.17487/RFC5308, October 2008.
[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.
[RFC5311]	McPherson, D., Ginsberg, L., Previdi, S. and M. Shand, "Simplified Extension of Link State PDU (LSP) Space for IS-IS", RFC 5311, DOI 10.17487/RFC5311, February 2009.
[RFC5316]	Chen, M., Zhang, R. and X. Duan, "ISIS Extensions in Support of Inter-Autonomous System (AS) MPLS and GMPLS Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316, December 2008.
[RFC6119]	Harrison, J., Berger, J. and M. Bartlett, "IPv6 Traffic Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119, February 2011.
[RFC7370]	Ginsberg, L., "Updates to the IS-IS TLV Codepoints Registry", RFC 7370, DOI 10.17487/RFC7370, September 2014.
[RFC7981]	Ginsberg, L., Previdi, S. and M. Chen, "IS-IS Extensions for Advertising Router Information", RFC 7981, DOI 10.17487/RFC7981, October 2016.
[RFC8174]	Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8200]	Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017.
[RFC8402]	Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S. and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018.

11.2. Informative References

[capreg]	, "Sub-TLVs for TLV 242 (IS-IS Router CAPABILITY TLV)", August 1987.
[loosereg]	, "Sub-TLVs for TLVs 135, 235, 236, and 237 (Extended IP reachability, MT IP. Reach, IPv6 IP. Reach, and MT IPv6 IP. Reach TLVs)", August 1987.
[strictreg]	, "Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223 (Extended IS reachability, IS Neighbor Attribute, L2 Bundle Member Attributes, inter-AS reachability information, MT-ISN, and MT IS Neighbor Attribute TLVs)", August 1987.

Authors' Addresses

Parag Kaneriya Juniper Networks Elnath-Exora Business Park Survey Bangalore, Karnataka 560103 India EMail: pkaneria@juniper.net

Rejesh Shetty Juniper Networks Elnath-Exora Business Park Survey Bangalore, Karnataka 560103 India EMail: mrajesh@juniper.net

Shraddha Hegde Juniper Networks Elnath-Exora Business Park Survey Bangalore, Karnataka 560103 India EMail: shraddha@juniper.net

Ron Bonica Juniper Networks 2251 Corporate Park Drive Herndon, Virginia 20171 USA EMail: rbonica@juniper.net