Interdomain Routing Working Group C. Li
Internet-Draft M. Chen
Intended status: Standards Track J. Dong
Expires: April 25, 2019 Z. Li
Huawei Technologies
October 22, 2018
SR Policies for Path Segment and Bidirectional Path in BGP-LS
draft-li-idr-bgp-ls-sr-policy-path-segment-01
Abstract
This document specifies the way of collecting configuration and
states of SR policies carrying Path Segment and bidirectional path
information by using BPG-LS. Such information can be used by
external conponents for many use cases such as performance
measurement, path re-optimization and end-to-end protection.
Requirements Language
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].
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 April 25, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Carrying SR Path Sub-TLVs in BGP-LS . . . . . . . . . . . . . 3
3.1. SR Path Segment Sub-TLV . . . . . . . . . . . . . . . . . 4
3.2. Sub-TLVs for Bidirectional Path . . . . . . . . . . . . . 5
3.2.1. SR Bidirectional Path Sub-TLV . . . . . . . . . . . . 5
3.2.2. SR Reverse Path Segment List Sub-TLV . . . . . . . . 6
4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Segment routing (SR) [RFC8402] is a source routing paradigm that
allows the ingress node steers packets into a specific path according
to the Segment Routing Policy
[I-D.ietf-spring-segment-routing-policy].
However, the SR Policies defined in
[I-D.ietf-spring-segment-routing-policy] only supports unidirectional
SR paths and there is no path ID in a Segment List to identify an SR
path. For identifying an SR path and supporting bidirectional path
[I-D.cheng-spring-mpls-path-segment], new policies carrying Path
Segment and bidirectional path information are defined in
[I-D.li-idr-sr-policy-path-segment-distribution], as well as the
extensions to BGP to distribute new SR policies. The Path Segment
can be a Path Segment in SR-MPLS [I-D.cheng-spring-mpls-path-segment]
, or a Path Segment in SRv6 [I-D.li-spring-srv6-path-segment], or
other IDs that can identify a path.
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In many network scenarios, the configuration and state of each TE
Policy is required by a controller which allows the network operator
to optimize several functions and operations through the use of a
controller aware of both topology and state information
[I-D.ietf-idr-te-lsp-distribution].
To collect the TE Policy information that is locally available in a
router, [I-D.ietf-idr-te-lsp-distribution] describes a new mechanism
by using BGP-LS update messages.
Based on the mechanism defined in [I-D.ietf-idr-te-lsp-distribution],
this document describes a mechanism to distribute configuration and
states of the new SR policies defined in
[I-D.li-idr-sr-policy-path-segment-distribution] to external
components using BGP-LS.
2. Terminology
This memo makes use of the terms defined in [RFC8402] and
[I-D.ietf-idr-te-lsp-distribution].
3. Carrying SR Path Sub-TLVs in BGP-LS
A mechanism to collect states of SR Policies via BGP-LS is proposed
by [I-D.ietf-idr-te-lsp-distribution]. The characteristics of an SR
policy can be described by a TE Policy State TLV, which is carried in
the optional non-transitive BGP Attribute "LINK_STATE Attribute"
defined in [RFC7752]. The TE Policy State TLV contains several sub-
TLVs such as SR TE Policy sub-TLVs. Rather than replicating SR TE
Policy sub-TLVs, [I-D.ietf-idr-te-lsp-distribution] reuses the
equivalent sub-TLVs as defined in
[I-D.ietf-idr-segment-routing-te-policy].
As defined in [I-D.li-idr-sr-policy-path-segment-distribution], the
new SR policies for bidirectional path has the following format:
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SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes: Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
Preference
Priority
Policy Name
Explicit NULL Label Policy (ENLP)
Bidirectioanl Path
Segment List
Weight
Path Segment
Segment
Segment
...
Reverse Segment List
Weight
Path Segment
Segment
Segment
...
Figure 1. SR policy for Bidirectional path
For collecting configuration and states of unidirectional and
bidirectional SR policies defined in
[I-D.li-idr-sr-policy-path-segment-distribution], new sub-TLVs in SR
TE Policy sub-TLVs should be defined. Likewise, rather than
replicating SR Policy sub-TLVs, this document can reuse the
equivalent sub-TLVs as defined in
[I-D.li-idr-sr-policy-path-segment-distribution].
3.1. SR Path Segment Sub-TLV
This section reuses the SR Path Segment sub-TLV defined in
[I-D.li-idr-sr-policy-path-segment-distribution] to describe a Path
Segment , and it can be included in the Segment List sub-TLV as
defined in [I-D.ietf-idr-te-lsp-distribution] . An SR Path Segment
sub-TLV can be associated with an SR path specified by a Segment List
sub-TLV, and it MUST appear only once within a Segment List sub-TLV.
Also, it can be used for identifying an SR candidate path or an SR
Policy defined in [I-D.ietf-spring-segment-routing-policy].
The format of Path Segment TLV is included below for reference.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flag | ST |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Segment (Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2. Path Segment sub-TLV
All fields, including type and length, are defined in
[I-D.li-idr-sr-policy-path-segment-distribution].
3.2. Sub-TLVs for Bidirectional Path
In some scenarios like mobile backhaul transport network, there are
requirements to support bidirectional path. In SR, a bidirectional
path can be represented as a binding of two unidirectional SR paths
[I-D.cheng-spring-mpls-path-segment].
[I-D.li-idr-sr-policy-path-segment-distribution] defines new sub-TLVs
to describe an SR bidirectional path. An SR policy carrying SR
bidirectional path information is expressed in Figure 1.
3.2.1. SR Bidirectional Path Sub-TLV
This section reuses the SR bidirectional path sub-TLV defined in
[I-D.li-idr-sr-policy-path-segment-distribution] to specify a
bidirectional path, which contains a Segment List sub-TLV
[I-D.ietf-idr-segment-routing-te-policy] and an associated Reverse
Path Segment List as defined in
[I-D.li-idr-sr-policy-path-segment-distribution]. The SR
bidirectional path sub-TLV has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3. SR Bidirectional path sub-TLV
All fields, including type and length, are defined in
[I-D.li-idr-sr-policy-path-segment-distribution].
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3.2.2. SR Reverse Path Segment List Sub-TLV
This section reuses the SR Reverse Path Segment List sub-TLV defined
in [I-D.li-idr-sr-policy-path-segment-distribution] to specify an
reverse SR path associated with the path specified by the Segment
List in the same SR Bidirectional Path Sub-TLV, and it has the
following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4. SR Reverse Path Segment List Sub-TLV
All fields, including type and length, are defined in
[I-D.li-idr-sr-policy-path-segment-distribution].
4. Operations
No new operation procedures are defined in this document, the
operations procedures of [RFC7752] can apply to this document.
Typically but not limited to, the uni/bidirectional SR policies
carrying path identification information can be distributed by the
ingress node.
Generally, BGP-LS is used for collecting link states and
synchronizing with the external component. The consumer of the uni/
bidirectional SR policies carrying path identification information is
not BGP LS process by itself, and it can be any applications such as
performance measurement [I-D.gandhi-spring-udp-pm] and path re-
coputation or re-optimization, etc. The operation of sending
information to other precesses is out of scope of this document.
5. IANA Considerations
TBA
6. Security Considerations
TBA
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7. Acknowledgements
TBA
8. References
8.1. Normative References
[I-D.cheng-spring-mpls-path-segment]
Cheng, W., Wang, L., Li, H., Chen, M., Gandhi, R., Zigler,
R., and S. Zhan, "Path Segment in MPLS Based Segment
Routing Network", draft-cheng-spring-mpls-path-segment-03
(work in progress), October 2018.
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Jain, D., Mattes, P., Rosen,
E., and S. Lin, "Advertising Segment Routing Policies in
BGP", draft-ietf-idr-segment-routing-te-policy-04 (work in
progress), July 2018.
[I-D.ietf-idr-te-lsp-distribution]
Previdi, S., Talaulikar, K., Dong, J., Chen, M., Gredler,
H., and J. Tantsura, "Distribution of Traffic Engineering
(TE) Policies and State using BGP-LS", draft-ietf-idr-te-
lsp-distribution-09 (work in progress), June 2018.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
bogdanov@google.com, b., and P. Mattes, "Segment Routing
Policy Architecture", draft-ietf-spring-segment-routing-
policy-01 (work in progress), June 2018.
[I-D.li-idr-sr-policy-path-segment-distribution]
Li, C., Chen, M., Dong, J., and Z. Li, "Segment Routing
Policies for Path Segment and Bi-directional Path", draft-
li-idr-sr-policy-path-segment-distribution-00 (work in
progress), April 2018.
[I-D.li-spring-srv6-path-segment]
Li, C., Chen, M., Dhody, D., Li, Z., Dong, J., and R.
Gandhi, "Path Segment for SRv6 (Segment Routing in IPv6)",
draft-li-spring-srv6-path-segment-00 (work in progress),
October 2018.
[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>.
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[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[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>.
8.2. Informative References
[I-D.gandhi-spring-udp-pm]
Gandhi, R., Filsfils, C., daniel.voyer@bell.ca, d.,
Salsano, S., Ventre, P., and M. Chen, "UDP Path for In-
band Performance Measurement for Segment Routing
Networks", draft-gandhi-spring-udp-pm-02 (work in
progress), September 2018.
[I-D.ietf-mpls-bfd-directed]
Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen,
"Bidirectional Forwarding Detection (BFD) Directed Return
Path", draft-ietf-mpls-bfd-directed-10 (work in progress),
September 2018.
Authors' Addresses
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: chengli13@huawei.com
Mach(Guoyi) Chen
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: Mach.chen@huawei.com
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Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: jie.dong@huawei.com
Zhenbin Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: lizhenbin@huawei.com
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