The Use of Path Segment in SR-MPLS and MPLS Interworking
draft-xiong-mpls-path-segment-sr-mpls-interworking-00
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| Authors | Quan Xiong , Greg Mirsky , Weiqiang Cheng | ||
| Last updated | 2019-07-03 | ||
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draft-xiong-mpls-path-segment-sr-mpls-interworking-00
MPLS Quan Xiong
Internet-Draft Greg Mirsky
Intended status: Standards Track ZTE Corporation
Expires: January 4, 2020 Weiqiang Cheng
China Mobile
July 3, 2019
The Use of Path Segment in SR-MPLS and MPLS Interworking
draft-xiong-mpls-path-segment-sr-mpls-interworking-00
Abstract
This document discusses the SR-MPLS and MPLS interworking scenarios
and proposes the solution with the use of Path Segment.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. SR-MPLS Interworking with MPLS . . . . . . . . . . . . . . . 3
3.1. Stitching interworking with i-Path . . . . . . . . . . . 4
3.2. Nesting interworking with e-Path . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Segment Routing (SR) leverages the source routing paradigm. A node
steers a packet through a SR Policy instantiated as an ordered list
of instructions called "segments". SR supports per-flow explicit
routing while maintaining per-flow state only at the ingress nodes of
the SR domain. Segment Routing can be instantiated on MPLS data
plane which is referred to as SR-MPLS
[I-D.ietf-spring-segment-routing-mpls]. SR-MPLS leverages the MPLS
label stack to construct the SR path.
In some scenarios, for example, mobile backhaul transport network, it
is required to provide end-to-end bidirectional tunnel across
multiple domains. IP/MPLS technology can be deployed in these
domains which may be access network, aggregation network or core
network under the control of a single operator. With the SR
architecture, the IP/MPLS may be upgraded to support the SR-MPLS
technology. There are requirements to support the interworking
between MPLS and SR-MPLS neworks at the boundaries and provide end-
to-end bidirectional service.
[I-D.ietf-spring-mpls-path-segment] defined a Path Segment identifier
to support SR path PM, end-to-end 1+1 SR path protection and
bidirectional SR paths correlation. This document discusses the
interworking scenarios between SR-MPLS and MPLS networks and proposes
the solution with the use of Path Segment.
2. Conventions used in this document
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2.1. Terminology
ABR: Area Border Routers. Routers used to connect two IGP areas
(areas in OSPF or levels in IS-IS).
AS: Autonomous System. An Autonomous System is composed by one or
more IGP area.
ASBR: Autonomous System Border Router. Router used to connect
together ASes of the same or different service providers via one or
more inter-AS links.
Border Node: Two IGP areas interconnects with an ABR.
Border Link: Two ASes interconnects with an ASBR.
Domains:Autonomous System (AS) or IGP Area. An Autonomous System is
composed by one or more IGP area.
e-Path: End-to-end Path segment.
IGP: Interior Gateway Protocol.
i-Path/i-PSID: Inter-domain Path Segment.
PM: Performance Measurement.
SR: Segment Routing.
SR-MPLS: Segment Routing with MPLS data plane.
s-Path: Sub-path Path Segment.
VPN: Virtual Private Network.
2.2. 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-MPLS Interworking with MPLS
It is required to establish the end-to-end VPN service across the
access network, aggregation network and core network. For example,
SR-MPLS may be deployed in access and core network and MPLS may be
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deployed in aggregation network. The network interworking should be
taken into account in deployment are the following:
o Border Node or Border Link
o Stitching Model or Nesting Model
o End-to-End OAM or Per-domain OAM
The domains of the networks may be IGP Areas or ASes. The SR-MPLS
and MPLS networks can be interconnect with border node between IGP
Areas or border link between ASes. This document takes IGP Areas
domains for example. MPLS domain can be deployed between two SR-MPLS
domains as Figure 1 shown. The packets being transmitted along the
SR path in SR-MPLS domains by using the SID list at the ingress node.
And the path in MPLS domains can be pre-configuration either via NMS
or via the MPLS control plane signaling.
B E X
+ + . . + +
+ + . . + +
+ + . . + +
A SR-MPLS C MPLS G SR-MPLS Z
+ IGP 1 + . IGP 2 . + IGP 3 +
+ + . . + +
+ + . . + +
D F Y
|<---Access Network--->|<-Aggregation Network->|<----Core Network---->|
Figure 1: SR-MPLS and MPLS interworking Scenario
The VPN service across the SR-MPLS and MPLS domains is an end-to-end
bidirectional path. In the SR-MPLS network, a Path Segment uniquely
identifies an SR path and can be used for bidirectional path. This
document proposed the solution of Path Segment used in interworking
scenario including the stitching and nesting models.
3.1. Stitching interworking with i-Path
It is a common requirement that SR-MPLS needs to interwork with MPLS
when SR is incrementally being deployed in the MPLS domain. Figure 2
shows the stitching model of SR-MPLS inter-working with MPLS.
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The end-to-end bidirectional path acrossing the SR-MPLS and MPLS
network being split into multiple segments. And each segment can be
identified by an inter-domain path segment (i-Path or i-PSID) as
defined in draft-xiong-spring-path-segment-sr-inter-domain. The
i-Pathis valid in the corresponding domain and the border nodes
maintain the forwarding entries of that i-Path segment binding the
next i-Path and the related labels, e.g, SID list or MPLS labels. In
the headend node, the i-Path can correlate the inter-domain path of
reverse direction and bind the two unidirectional paths.
+-----------------+ ................ +-----------------+
| +---+ | . +---+ . | +---+ |
| | B | | . | E | . | | X | |
| +---+ | . +---+ . | +---+ |
| / \ | . / \ . | / \ |
| +---+ SR-MPLS +-----+ MPLS +-----+ SR-MPLS +---+ |
| | A | domain1 | C | domain2 | G | domain3 | Z | |
| +---+ +-----+ +-----+ +---+ |
| \ / | . \ / . | \ / |
| +---+ | . +---+ . | +---+ |
| | D | | . | F | . | | Y | |
| +---+ | . +---+ . | +---+ |
+-----------------+ ................ +-----------------+
|<----SID List---->|<--- MPLS Label--->|<----SID List---->|
|<-----i-Path----->|<------i-Path----->|<-----i-Path----->|
|<----------------------VPN Service---------------------->|
Figure 2: SR-MPLS and MPLS interworking with Path Segment
3.2. Nesting interworking with e-Path
Figure 3 displays the nesting model of SR-MPLS and MPLS interworking.
Compared with stitching model, the path segment presents end-to-end
encapsulation in the packet from SR-MPLS domain to MPLS domain. As
described in [I-D.ietf-spring-mpls-path-segment], an end-to-end path
segment, also referred to as e-Path, is used to indicate the end-to-
end path, and an s-Path is used to indicate the intra-domain path.The
e-Path is encapsulated at the ingress nodes and decapsulated at the
egress nodes. The transit nodes, even the border nodes of domains,
are not aware of the e-Path segment. The s-Path can be used as
stitching label to correlate the two domains. The use of the binding
SID [RFC8402] is also recommended to reduce the size of lable stack.
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+-----------------+ ................ +-----------------+
| +---+ | . +---+ . | +---+ |
| | B | | . | E | . | | X | |
| +---+ | . +---+ . | +---+ |
| / \ | . / \ . | / \ |
| +---+ SR-MPLS +-----+ MPLS +-----+ SR-MPLS +---+ |
| | A | domain1 | C | domain2 | G | domain3 | Z | |
| +---+ +-----+ +-----+ +---+ |
| \ / | . \ / . | \ / |
| +---+ | . +---+ . | +---+ |
| | D | | . | F | . | | Y | |
| +---+ | . +---+ . | +---+ |
+-----------------+ ................ +-----------------+
|<----SID List---->|<-- MPLS Label-->|<----SID List---->|
|<-----s-Path----->|<------s-Path----->|<-----s-Path----->|
|<------------------------e-Path------------------------->|
|<----------------------VPN Service---------------------->|
Figure 3: Nesting SR-MPLS inter-working with MPLS
4. Security Considerations
TBA
5. Acknowledgements
TBA
6. IANA Considerations
TBA
7. Normative References
[I-D.ietf-spring-mpls-path-segment]
Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler,
"Path Segment in MPLS Based Segment Routing Network",
draft-ietf-spring-mpls-path-segment-00 (work in progress),
March 2019.
[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-22
(work in progress), May 2019.
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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>.
[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>.
Authors' Addresses
Quan Xiong
ZTE Corporation
No.6 Huashi Park Rd
Wuhan, Hubei 430223
China
Phone: +86 27 83531060
Email: xiong.quan@zte.com.cn
Greg Mirsky
ZTE Corporation
USA
Email: gregimirsky@gmail.com
Weiqiang Cheng
China Mobile
Beijing
China
Email: chengweiqiang@chinamobile.com
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