IDR Working Group Yao. Liu
Internet-Draft Shaofu. Peng
Intended status: Standards Track ZTE Corp.
Expires: February 22, 2021 August 21, 2020
BGP Extension for SR-MPLS Entropy Label Position
draft-zhou-idr-bgp-srmpls-elp-01
Abstract
This document proposed an extension for BGP to configure the entropy
label position for SR-MPLS networks.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Entropy Labels in SR-MPLS Scenario with a Controller . . . . 2
3. BGP Extensions . . . . . . . . . . . . . . . . . . . . . . . 3
4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
Entropy Label(EL) [RFC6790]is a technology that can be used for load-
balancing in Segment Routing (SR) MPLS.
[RFC8662] proposes to use entropy labels for SR-MPLS networks and
mutiple < ELI, EL> pairs SHOULD 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, the
controller is 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 in the SR network passes the path calculation
result of the SR-TE policy to the headend of the network through BGP.
In this document, the ELP information is transmitted by extending the
flags of Segment List Sub-TLV in the BGP.
2. 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.
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As shown in Figure 1 , in SR-MPLS inter-domain scenario, the
controller may perform the computation of the end-to-end path as well
as the the Entropy Label Position (ELP) including the number and the
position of the ELI/ELs. The controller has the capability to get
the ERLD information of all nodes in inter-domain scenarios.
.................... .................... .....................
. . . . . .
.+---+ +---+ . . +---+ +---+ . .+---+ +----+ .
.| A |-------| B |------ | C |------| X |-------| Y |------| Z | .
.+---+ +---+ . . +---+ +---+ . .+---+ +----+ .
. domain 1 . . domain 2 . . domain 3 .
.................... .................... .....................
Figure 1: Entropy Labels in SR-MPLS Inter-Domain Scenario
3. BGP Extensions
The Segment Flags is defined in Section 2.4.3.2.12 of
[I-D.ietf-idr-segment-routing-te-policy].
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|V|A|E| |
+-+-+-+-+-+-+-+-+
E-Flag: This flag indicates that presence of < ELI, EL> label pairs
are inserted after this segment. It is applicable to all SR-MPLS
Segment Types.
4. Operations
Supposed the head end had received a SR-TE path from the controller
with multiple Segment List Sub-TLVs, for example, <S1, S2, S3, S4,
S5, S6>, especially S3 and S6 with E-flag. It indicates that 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. With EL information, the label stack for SR-MPLS would be
<label1, label2, label3, ELI, EL, label4, label5, label6, ELI, EL>.
Note that the value of EL is supplemented by headend, according to
load-balancing function of the appropriate keys extracted from a
given packet.
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5. IANA Considerations
This document requests bit 2 for Entropy Label Flag.
Bit Description Reference
------------------------------------------------------------------
2 Entropy Label Position Flag(E-Flag) This document
6. 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-09 (work in progress), May 2020.
[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>.
[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>.
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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