IDR Working Group Yao. Liu
Internet-Draft Shaofu. Peng
Intended status: Standards Track ZTE Corp.
Expires: August 26, 2021 February 22, 2021
BGP Extension for SR-MPLS Entropy Label Position
draft-zhou-idr-bgp-srmpls-elp-02
Abstract
This document proposes extensions for BGP to indicate the entropy
label position in the SR-MPLS label stack when distributing SR Policy
candidate paths.
Status of This Memo
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This Internet-Draft will expire on August 26, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Terminology and Acronyms . . . . . . . . . . . . . . . . 3
3. Entropy Labels in SR-MPLS Scenario with a Controller . . . . 3
4. BGP Extensions . . . . . . . . . . . . . . . . . . . . . . . 4
5. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Segment Routing (SR) leverages the source routing paradigm. Segment
Routing can be instantiated on MPLS data plane which is referred to
as SR-MPLS [RFC8660]. SR-MPLS leverages the MPLS label stack to
construct the SR path.
Entropy labels (ELs) [RFC6790] are used in the MPLS data plane to
provide entropy for load-balancing. The idea behind the entropy
label is that the ingress router computes a hash based on several
fields from a given packet and places the result in an additional
label named "entropy label". Then, this entropy label can be used as
part of the hash keys used by an LSR. Using the entropy label as
part of the hash keys reduces the need for deep packet inspection in
the LSR while keeping a good level of entropy in the load-balancing.
[RFC8662] proposes to use entropy labels for SR-MPLS networks and
mutiple < ELI, EL> pairs may be inserted in the SR-MPLS label stack.
The ingress node may decide the number and position of the ELI/ELs
which need to be inserted into the label stack, that is termed as ELP
(Entropy Label Position). In some cases, centralized controllers are
used to perform the TE path computation for intra or inter-domain
scenarios, thus it is also the responsibility of the controller to
calculate ELP and inform it to the headend of the SR-TE path.
[I-D.ietf-idr-segment-routing-te-policy] defines the specific process
of how the controller/PCE in the SR network passes the path
calculation result of the SR-TE policy to the headend of the network
through BGP.
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This document proposes extensions for BGP to indicate the ELP in the
segment list when distribute SR Policy candidate paths using BGP for
SR-MPLS networks.
2. Conventions used in this document
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.
2.2. Terminology and Acronyms
EL: Entropy Label
ELI: Entropy Label Indicator
ELC: Entropy Label Capability
ERLD: Entropy Readable Label Depth
ELP: Entropy Label Position
MSD: Maximum SID Depth
3. Entropy Labels in SR-MPLS Scenario with a Controller
[RFC8662] proposes to use entropy labels for SR-MPLS networks. The
Entropy Readable Label Depth (ERLD) is defined as the number of
labels which means that the router will perform load-balancing using
the ELI/EL. An appropriate algorithm should consider the following
criteria:
o a limited number of < ELI, EL> pairs SHOULD be inserted in the SR-
MPLS label stack;
o the inserted positions SHOULD be whithin the ERLD of a maximize
number of transit LSRs;
o a minimum number of < ELI, EL> pairs SHOULD be inserted while
satisfying the above criteria.
As shown in Figure 1, in SR-MPLS inter-domain scenario, an path from
A to Z is required, a centralized controller performs the computation
of the end-to-end path, along which traffic load-balancing is
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required. The controller can also be used to perform the computation
of the the Entropy Label Position (ELP) of the segment list that
corresponds to the path. The ELP includs the number and the position
of the ELI/ELs.
Multiple limitations MUST be taken into account by the controller
during path calculation, including Entropy Readable Label Depth
(ERLD) and Maximum SID Depth (MSD) etc. The ERLD is defined as the
number of labels which means that the node will perform load-
balancing using the ELI/EL pairs. And each ELI/EL pair must be
within the ERLD of the node. The Maximum SID Depth (MSD) defines the
maximum number of any kind of labels(service, entropy, transport,
etc.) and it is a limit when the ingress node imposing ELI/EL pairs
on the SR label stack.
The controller can get ERLD value and MSD via protocols. The ERLD
value can be advertised via IS-IS[I-D.ietf-isis-mpls-elc],
OSPF[I-D.ietf-ospf-mpls-elc], BGP-
LS[I-D.ietf-idr-bgp-ls-segment-routing-ext]. [RFC8476], [RFC8491],
and[RFC8814] provide examples of advertisement of the MSD.
As specified in section 7.2 [RFC8662], other criteria includes
segment type, preference for a part of the path, and etc. It's a
matter of implementation.
.................... .................... .....................
. . . . . .
.+---+ +---+ . . +---+ +---+ . .+---+ +----+ .
.| A |-------| B |------ | C |------| X |-------| Y |------| Z | .
.+---+ +---+ . . +---+ +---+ . .+---+ +----+ .
. domain 1 . . domain 2 . . domain 3 .
.................... .................... .....................
Figure 1: Entropy Labels in SR-MPLS Inter-Domain Scenario
4. BGP Extensions
The Segment Flags for Segment Sub-TLVs are defined in
Section 2.4.4.2.12 of [I-D.ietf-idr-segment-routing-te-policy]. In
this document, the ELP information is transmitted by extending the
flags of Segment Sub-TLVs.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|V|A|S|B|E| |
+-+-+-+-+-+-+-+-+
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E-Flag: This flag, when set, indicates that presence of < ELI, EL>
label pairs which are inserted after this segment. E-Flag is
applicable to Segment Types A, C, D, E, F, G and H. If E-Flag
appears with Segment Types B, I, J and K, it MUST be ignored. .
5. Operations
Node A receives an SR Policy NLRI with an Segment List sub-TLV from
the controller. The Segment List sub-TLV contains multiple Segment
sub-TLVs, for example, <S1, S2, S3, S4, S5, S6>, the E-Flags of S3
and S6 are set, it indicates that if load-balancing is required, two
<ELI, EL> pairs SHOULD be inserted into the label stack of the SR-TE
forwarding entry, respectively after the Label for S3 and Label for
S6.
The value of EL is supplemented by the ingress node according to
load-balancing function of the appropriate keys extracted from a
given packet. After inserting ELI/ELs, the label stack on the
ingress node would be <label1, label2, label3, ELI, EL, label4,
label5, label6, ELI, EL>.
6. Security Considerations
TBD
7. IANA Considerations
This document requests bit 4 for Entropy Label Flag.
Bit Description Reference
------------------------------------------------------------------
4 Entropy Label Position Flag(E-Flag) This document
8. References
8.1. Normative References
[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), November 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>.
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[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[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>.
[RFC8662] Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
Shakir, R., and J. Tantsura, "Entropy Label for Source
Packet Routing in Networking (SPRING) Tunnels", RFC 8662,
DOI 10.17487/RFC8662, December 2019,
<https://www.rfc-editor.org/info/rfc8662>.
8.2. Informative References
[I-D.ietf-idr-bgp-ls-segment-routing-ext]
Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
and M. Chen, "BGP Link-State extensions for Segment
Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
(work in progress), June 2019.
[I-D.ietf-isis-mpls-elc]
Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
and M. Bocci, "Signaling Entropy Label Capability and
Entropy Readable Label Depth Using IS-IS", draft-ietf-
isis-mpls-elc-13 (work in progress), May 2020.
[I-D.ietf-ospf-mpls-elc]
Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
and M. Bocci, "Signaling Entropy Label Capability and
Entropy Readable Label Depth Using OSPF", draft-ietf-ospf-
mpls-elc-15 (work in progress), June 2020.
[RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
"Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,
DOI 10.17487/RFC8476, December 2018,
<https://www.rfc-editor.org/info/rfc8476>.
[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/info/rfc8491>.
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[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[RFC8814] Tantsura, J., Chunduri, U., Talaulikar, K., Mirsky, G.,
and N. Triantafillis, "Signaling Maximum SID Depth (MSD)
Using the Border Gateway Protocol - Link State", RFC 8814,
DOI 10.17487/RFC8814, August 2020,
<https://www.rfc-editor.org/info/rfc8814>.
Authors' Addresses
Liu Yao
ZTE Corp.
Email: liu.yao71@zte.com.cn
Peng Shaofu
ZTE Corp.
Email: peng.shaofu@zte.com.cn
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