Inter-Domain Routing Working Group Y. Wang
Internet-Draft H. Li
Intended status: Standards Track Y. Qiu
Expires: August 2, 2021 L. Yang
M. Chen
H3C Technologies
February 2, 2021
Segment Routing PCE Delegation in BGP
draft-wang-idr-sr-policy-pce-delegation-00
Abstract
Segment Routing is a source routing paradigm that explicitly
indicates the forwarding path for packets at the ingress node. An
SR policy is a set of candidate SR paths consisting of one or more
segment lists with necessary path attributes. The headend of an SR
Policy may learn multiple candidate paths for an SR Policy.
Candidate paths may be learned via a number of different mechanisms,
e.g., CLI, NetConf, PCEP, or BGP.
The Path Computation Element (PCE) provides path computation
functions in support of traffic engineering in Multi Protocol Label
Switching (MPLS) and Generalized MPLS (GMPLS) networks.
Currently, when a controller uses BGP to deploy an SR Policy, there
is no way to encode PCE delegation related options. The only way to
import a PCE delegation is through local configuration management,
e.g., Netconf, CLI or gRPC.
This document defines extensions to BGP to distribute PCE
delegation information within an SR policy.
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
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 2, 2021.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. SR Policy for PCE Delegation. . . . . . . . . . . . . . . . . 4
3.1. PCE Delegation Sub-TLV . . . . . . . . . . . . . . . . . 6
4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
Segment routing (SR) [RFC8402] is a source routing paradigm that
explicitly indicates the forwarding path for packets at the
ingress node. The ingress node steers packets into a specific
path according to the Segment Routing Policy (SR Policy) as
defined in[I-D.ietf-spring-segment-routing-policy]. In order
to distribute SR policies to the headend,
[I-D.ietf-idr-segment-routing-te-policy] specifies a mechanism by
using BGP.
[RFC5440] describes the Path Computation Element (PCE) Communication
Protocol (PCEP). PCEP enables the communication between a Path
Computation Client (PCC) and a PCE, or between PCE and PCE, for the
purpose of computation of Multi protocol Label Switching (MPLS) as
well as Generalized MPLS (GMPLS) Traffic Engineering Label Switched
Path (TE LSP) characteristics.
When a controller uses BGP deploy an SR Policy, The only way to
import a PCE delegation is through configuration management e.g.,
Netconf, CLI or gRPC. It's inconvenient for a controller to use
separate channels to deploy SR policies.
This document defines extensions to BGP to distribute PCE delegation
information within SR policies.
2. Terminology
PCE delegation : An operation to grant a PCE temporary rights to
modify a subset of LSP parameters on one or more PCC's LSPs. LSPs
are delegated from a PCC to a PCE, and are referred to as delegated
LSPs. The PCC who owns the PCE state for the LSP has the right to
delegate it. An LSP is owned by a single PCC at any given point
in time. For intra-domain LSPs, this PCC SHOULD be the PCC of the
LSP head end.
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2.1. 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. SR Policy for PCE Delegation
As defined in [I-D.ietf-idr-segment-routing-te-policy] , the SR
policy encoding structure is as follows:
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)
Segment List
Weight
Segment
Segment
...
...
As introduced in Section 1, SR Policy could use PCE to calculate
path. SR policy with PCE delegation information is expressed as
below:
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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
PCE Delegation
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment
Segment
...
...
3.1. PCE Delegation Sub-TLV
A PCE Delegation sub-TLV is an Optional sub-TLV. When it appears,
it must appear only once at most within a SR Policy Sub-TLV. If
multiple PCE Delegation sub-TLVs appear within an SR Policy Sub-TLV,
the NLRI MUST be treated as a malformed NLRI.
As per [I-D.ietf-idr-segment-routing-te-policy], when the error
determined allows for the router to skip the malformed NLRI(s) and
continue processing of the rest of the update message, then it MUST
handle such malformed NLRIs as 'Treat-as-withdraw'. This document
does not define new error handling rules for PCE Delegation sub-TLV,
and the error handling rules defined in
[I-D.ietf-idr-segment-routing-te-policy] apply to this document.
PCE Delegation is a new sub-TLV of the BGP Tunnel Encapsulation
Attribute [I-D.ietf-idr-tunnel-encaps].
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A PCE Delegation sub-TLV is associated with an SR policy. The PCE
Delegation 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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1. PCE Delegation sub-TLV
Where:
Type: to be assigned by IANA.
Length: the total length of the value field not including Type and
Length fields.
Flags: 1 octet of flags.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|D|R|
+-+-+-+-+-+-+-+-+
where:
* D-Flag: The flag encode PCE delegation. When this flag is set, it
indicates to enable PCE delegation function, otherwise it indicates
to disable PCE delegation.
* R-Flag: The flag encode passive delegation report only. An
implementation SHOULD report its the status of SR policies to PCE
server without using PCE Server to calculate path.
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To avoid confusion, D-Flag and R-Flag SHOULD NOT be set
simultaneously.
Unused bits in the Flag octet SHOULD be set to zero upon
transmission and MUST be ignored upon receipt.
Reserved: 8 bits reserved and MUST be set to 0 on transmission and
MUST be ignored on receipt.
4. Operations
The document does not bring new operation beyond the description of
operations defined in [I-D.ietf-idr-segment-routing-te-policy]. The
existing operations defined in
[I-D.ietf-idr-segment-routing-te-policy] can apply to this document
directly.
Typically but not limit to, the SR policies carrying PCE Delegation
information are configured by a controller.
After configuration, the SR policies carrying PCE Delegation
information will be advertised by BGP update messages. The operation
of advertisement is the same as defined in
[I-D.ietf-idr-segment-routing-te-policy], as well as the reception.
The consumer of the SR policies is not the BGP process. The
operation of sending information to consumers is out of scope of this
document.
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5. IANA Considerations
This document defines a new Sub-TLV in registries "SR Policy List
Sub- TLVs" [I-D.ietf-idr-segment-routing-te-policy]:
Value Description Reference
---------------------------------------------------------------------
TBA PCE Delegation sub-TLV This document
6. Security Considerations
TBA
7. Contributors
Yang.Wang
H3C Technology
China
Email: wang.a.yang@h3c.com
8. Acknowledgements
Authors would like to thank Changwang.Lin, Jinrong.Ye for their
proprefessional comments and help.
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9. References
9.1. Normative References
[I-D.ietf-idr-tunnel-encaps]
Patel, K., Velde, G., Sangli, S., and J. Scudder, "The BGP
Tunnel Encapsulation Attribute", draft-ietf-idr-tunnel-
encaps-22 (work in progress), January 2021.
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
Rosen, E., Jain, D., and S. Lin, "Advertising Segment
Routing Policies in BGP", draft-ietf-idr-segment-routing-
te-policy-11 (work in progress), May 2020.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-09 (work in progress),
July 2020.
[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>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[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>.
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Authors' Addresses
Yang Wang
H3C Technologies
China
Email: wang.a.yang@h3c.com
Hao Li
H3C Technologies
China
Email: lihao@h3c.com
Yuanxiang Qiu
H3C Technologies
China
Email: qiuyuanxiang@h3c.com
Liping Yang
H3C Technologies
China
Email: liping_yang@h3c.com
Mengxiao Chen
H3C Technologies
China
Email: chen.mengxiao@h3c.com
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