LSR WG Ran. Chen
Internet-Draft Shaofu. Peng
Intended status: Standards Track ZTE Corporation
Expires: November 9, 2020 May 8, 2020
IGP Extensions for Shorter SRv6 SID
draft-chen-lsr-igp-shorter-srv6-extensions-02
Abstract
This document describes the IGP extensions required to support the
Shorter SRv6 SIDs( Compressing SRv6 SIDs).
Status of This Memo
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This Internet-Draft will expire on November 9, 2020.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Advertising Shorter SRv6 SIDs capabilities. . . . . . . . . . 2
2.1. IS-IS Extensions . . . . . . . . . . . . . . . . . . . . 2
2.2. OSPFv3 Extensions . . . . . . . . . . . . . . . . . . . . 4
3. Advertising SRv6 SID Structure Sub-Sub-TLV . . . . . . . . . 5
4. Advertising Endpoint Behaviors with U-Flavor . . . . . . . . 6
5. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Segment Routing [RFC8402] leverages the source routing paradigm. An
ingress node steers a packet through an ordered list of
instructions,called segments.
Segment Routing can be directly instantiated on the IPv6 data plane
through the use of the Segment Routing Header defined in [RFC8754].
SRv6 refers to this SR instantiation on the IPv6 dataplane.
However, the size of the SRv6 SID presents a scalabilities challenge
to use topological instructions that define a strict explicitly
routed path in combination with service-based instructions. At the
same time, the size of the SRH/SID may be a challenge for some data
plane processors and traffic overhead.
[I-D.cheng-spring-shorter-srv6-sid-requirement] describes a list of
requirements for the use of a shortened identifier in a segment
routing network with the IPv6 data plane.
[I-D.mirsky-6man-unified-id-sr] proposed an extension of SRH that
enables the use of a shorter segment identifier in dataplane, such as
32-bits Label format SID or 32-bits IP address format SID.
This document defines extensions to IGP in order to to support the
Shorter SRv6 SIDs contained in SID list that installed in dataplane.
2. Advertising Shorter SRv6 SIDs capabilities.
2.1. IS-IS Extensions
A node indicates that it supports the SR Segment Endpoint Node
functionality as specified in [RFC8754] by advertising a new SRv6
Capabilities sub-TLV [I-D.ietf-lsr-isis-srv6-extensions] of the
router capabilities TLV [RFC7981].
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This document extensions the flags field in the SRv6 Capabilities
sub-TLV [I-D.ietf-lsr-isis-srv6-extensions] to indicate the node
supports the Shorter SRv6 SIDs.
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 |U|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional sub-sub-TLVs...
Figure 1: U-Flag in SRv6 Capabilities sub-TLV
where
U: U-SID Encapsulation Capability. When the U flag is set, it
indicates that the node supports the encapsulate and decapsulate the
U-SID, that is to say, the SID list composed of multiple classic 128
bit SIDs can be compressed into an U-SID list containing multiple
shorter U-SIDs, which is encapsulated in SRH, or the shorter U-SID
can be obtained from SRH and restored to the classic 128 bit SID.
Optional sub-sub-TLVs: When the U flag is set, A new U-Domain sub-
sub-TLV is carried to describe which compression domain (U-Domain)
the node is in. If the U-Domain sub-sub-tlv is not carried, it is in
32-bit compression domain by default. Note that each node is always
in the classical 128 bit compression domain, without explicit
notification.
The format of the U-Domain sub-Sub-TLV is as 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-Type=U-D | Length | Flags |M|S|T|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2:U-Domain sub-Sub-TLV
Three flags are currently defined in the U-Domain sub-Sub-TLV:
T: The node is in 32-bit compression domain.
S: The node is in 16-bit compression domain.
M: The node is in MPLS compression domain.
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Note that the U-SID Encapsulation capability has nothing to do with
the type of compression domain the node is in. For example, an N1
node in a 128 bit compression domain has U-SID Encapsulation
capability, while an N2 node in the same domain may not have U-SID
Encapsulation capability.
2.2. OSPFv3 Extensions
The SRv6 Capabilities TLV is used by an OSPFv3 router to advertise
its SRv6 support along with its related capabilities for SRv6
functionality. This is an optional top level TLV of the OSPFv3
Router Information LSA [RFC7770] which MUST be advertised by an SRv6
enabled router.
This document extensions the flags field in the SRv6 Capabilities TLV
[I-D.ietf-lsr-ospfv3-srv6-extensions] to indicate the node supports
the Shorter SRv6 SIDs.
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 |U| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: U-Flag in SRv6 Capabilities TLV
where
U: U-SID Encapsulation Capability. When the U flag is set, it
indicates that the node supports the encapsulate and decapsulate the
U-SID, that is to say, the SID list composed of multiple classic 128
bit SIDs can be compressed into an U-SID list containing multiple
shorter U-SIDs, which is encapsulated in SRH, or the shorter U-SID
can be obtained from SRH and restored to the classic 128 bit SID.
Sub-TLVs: When the U flag is set, A new U-Domain sub-TLV is carried
to describe which compression domain (U-Domain) the node is in. If
the U-Domain sub-tlv is not carried, it is in 32-bit compression
domain by default. Note that each node is always in the classical
128 bit compression domain, without explicit notification.
The format of the U-Domain sub-Sub-TLV is as below:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-Type=U-D | Length | Flags |M|S|T|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: U-Domain sub-TLV
Three flags are currently defined in the U-Domain sub-TLV:
T: The node is in 32-bit compression domain.
S: The node is in 16-bit compression domain.
M: The node is in MPLS compression domain.
Note that the U-SID Encapsulation capability has nothing to do with
the type of compression domain the node is in. For example, an N1
node in a 128 bit compression domain has U-SID Encapsulation
capability, while an N2 node in the same domain may not have U-SID
Encapsulation capability.
3. Advertising SRv6 SID Structure Sub-Sub-TLV
SRv6 SID Structure Sub-Sub-TLV is an optional Sub-Sub-TLV of SRv6 End
SID Sub-TLV, SRv6 End.U SID Sub-TLV ,and SRv6 LAN End.U SID Sub-TLV .
As discussed in [I-D.ietf-spring-srv6-network-programming], the node
with the SRv6 capability will maintain its local SID table. A Local
SID is generally composed of two parts, that is, LOC:FUNCT, or may
carry arguments at the same time, that is, LOC:FUNCT:ARGS. The
controller plane protocol can also use B:N to represent an LOC, where
B is SRv6 SID Locator Block and N to represent node N. In other
words, the structure of a complete SID is B:N:FUNCT:ARGS.
SRv6 SID Structure Sub-Sub-TLV [I-D.ietf-lsr-isis-srv6-extensions] or
SRv6 SID Structure Sub-TLV [I-D.ietf-lsr-ospfv3-srv6-extensions] is
used to advertise the length of each individual part of the SRv6 SID.
If a node advertised the compression domains which the node is in, it
SHOULD advertise the related SIDs with structure information,
otherwise the result optimized SID list will have to contain related
classical 128-bits SRv6 SID.
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4. Advertising Endpoint Behaviors with U-Flavor
Endpoint behaviors are defined in
[I-D.ietf-spring-srv6-network-programming]
and[I-D.ietf-6man-spring-srv6-oam] . The codepoints for the Endpoint
behaviors are defined in the "SRv6 Endpoint Behaviors" registry
defined in [I-D.ietf-spring-srv6-network-programming]. For End,
End.X and End.T behaviors, they can also have PSP, USP and USD
variants. This document continues to extend the following new
flavors for End and End.X behaviors:
U32-Flavor: indicate the next SID is 32-bits IP address.
U16-Flavor: indicate the next SID is 16-bits IP address.
We can take regard the traditional behaviors that has not any
indication of next SID type as behaviors with U128-flavor.
To extend the above U related flavors for other endpoint behaviors,
such as VPN related SID and SFC related SID, is out the scope of this
document.
Note that a SID MUST NOT set two or more of the above flavors at the
same time, because these flavors is used to indicate the next SID
type in SRH, that is, the local SID entry must provide exact
indication for this purpose.
Each of the above U related flavors can be used combined with
existing PSP/USP/USD flavors.
5. Operations
Based on the IGP link-state database which contains U-SID
Encapsulation Capabilities and SID(s) per U-Flavors, a headend or
controller can firstly check which compression domains a computed SR
path crossed, then secondly select U-Flavor related SID to construct
an optimized E2E SID list.
The detailed description can refer to [I-D.mirsky-6man-unified-id-sr]
and [I-D.liu-idr-segment-routing-te-policy-complement].
6. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the security considerations discussed in [I-D.ietf-lsr-isis-sr
v6-extensions]and[I-D.ietf-lsr-ospfv3-srv6-extensions] .
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7. IANA Considerations
TBD
8. Normative References
[I-D.cheng-spring-shorter-srv6-sid-requirement]
Cheng, W., Xie, C., Pang, R., Li, Z., Chen, R., Lijun, L.,
Duan, X., and G. Mirsky, "Shorter SRv6 SID Requirements",
draft-cheng-spring-shorter-srv6-sid-requirement-01 (work
in progress), March 2020.
[I-D.ietf-6man-spring-srv6-oam]
Ali, Z., Filsfils, C., Matsushima, S., Voyer, D., and M.
Chen, "Operations, Administration, and Maintenance (OAM)
in Segment Routing Networks with IPv6 Data plane (SRv6)",
draft-ietf-6man-spring-srv6-oam-04 (work in progress),
March 2020.
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extension to Support Segment Routing over
IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-08
(work in progress), April 2020.
[I-D.ietf-lsr-ospfv3-srv6-extensions]
Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak,
"OSPFv3 Extensions for SRv6", draft-ietf-lsr-
ospfv3-srv6-extensions-00 (work in progress), February
2020.
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
Matsushima, S., and Z. Li, "SRv6 Network Programming",
draft-ietf-spring-srv6-network-programming-15 (work in
progress), March 2020.
[I-D.liu-idr-segment-routing-te-policy-complement]
Yao, L. and S. Peng, "BGP Extensions for Unified SID in TE
Policy", draft-liu-idr-segment-routing-te-policy-
complement-02 (work in progress), May 2020.
[I-D.mirsky-6man-unified-id-sr]
Cheng, W., Mirsky, G., Peng, S., Aihua, L., Wan, X., and
C. Wei, "Unified Identifier in IPv6 Segment Routing
Networks", draft-mirsky-6man-unified-id-sr-06 (work in
progress), March 2020.
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[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>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>.
[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
for Advertising Router Information", RFC 7981,
DOI 10.17487/RFC7981, October 2016,
<https://www.rfc-editor.org/info/rfc7981>.
[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>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
Authors' Addresses
Ran Chen
ZTE Corporation
No. 50 Software Ave, Yuhuatai Distinct
Nanjing
China
Email: chen.ran@zte.com.cn
Peng Shaofu
ZTE Corporation
No. 50 Software Ave, Yuhuatai Distinct
Nanjing
China
Email: peng.shaofu@zte.com.cn
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