Internet DRAFT - draft-hu-spring-sr-tp-use-case
draft-hu-spring-sr-tp-use-case
SPRING WG Fangwei Hu
Internet-Draft Quan Xiong
Intended status: Informational Greg Mirsky
Expires: September 5, 2018 ZTE Corporation
Weiqiang Cheng
China Mobile
Mar 4, 2018
Segment Routing Transport Profile Use Case
draft-hu-spring-sr-tp-use-case-01.txt
Abstract
This document discusses the use case and requirement of segment
routing is used in MPLS-TP network.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. SRTP Requirement . . . . . . . . . . . . . . . . . . . . . . 3
4. SRTP Use Case . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1. SRTP Scenario . . . . . . . . . . . . . . . . . . . . . . 3
4.2. SRTP Loose Constraints Path . . . . . . . . . . . . . . . 5
4.3. SRTP Strict Constraints Path . . . . . . . . . . . . . . 6
5. Bi-direction SRTP Tunnel Binding . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Normative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
With the wide spread adoption of virtualization and cloud computing,
the east-west traffic is greatly increased in the current MPLS-TP
network. This trend brought the new requirements for the MPLS-TP
networks:
(1) The access layer nodes should be meshed to provide the east-west
traffic forwarding capability.
(2) The access nodes should support signaling protocol and maintain
large volume of state for traffic engineering and tunnel
connection, which is very challenging for the access nodes in
the current MPLS-TP networks.
Segment Routing(SR)[I-D.ietf-spring-segment-routing] allows a node to
steer a packet through a controlled set of instructions, called
segments, by prepending an SR header to the packet. The transit
nodes forward the packet based on the segment list, and do not need
to maintain the service status. There is no need to run signaling
protocol in the traffic engineering network, which simplifies the
network deployment and operation. The Segment Routing architecture
can be directly applied to the MPLS dataplane with no change on the
forwarding plane [I-D.ietf-spring-segment-routing-mpls]. It requires
a minor extension to the existing link-state routing protocols.
If the segment routing technology is deployed in the current MPLS-TP
network, the challenge for the access layer nodes could be addressed.
The access layer nodes only need to support IGP protocol (ISIS,
OSPF), and they do not need to support signaling protocol and
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maintain traffic engineering status and tunnel information, which
simplifies the access layer nodes. The segment routing technology
being deployed in the MPLS-TP network is referred to as SRTP
technology. This document discusses uses case and requirements for
the SR-TP.
2. Conventions used in this document
2.1. Terminology
SRTP: segment routing transport profile. The segment routing is
deployed in the packet-switched transport networks.
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. SRTP Requirement
The requirement of SRTP are as following:
(1) It is required to support bi-direction tunnel to fit for the
requirement of packet-switched transport networks. The SR nodes
are required to announce the related capability and parameters
information to the centralized controller.
(2) It is required to support SRTP loose constraints traffic
engineering path for packet-switched transport networks.
(3) It is required to support SRTP strict constraints traffic
engineering path for packet-switched transport networks. The
data forwarding path is usually maintained by centralized
controller.
4. SRTP Use Case
4.1. SRTP Scenario
Figure 1 is a typical SRTP deployment scenario. The SR nodes run IGP
protocol extension for segment routing
([I-D.ietf-isis-segment-routing-extensions] or
[I-D.ietf-ospf-segment-routing-extensions]), and flood the SR
parameters to the network. The nodes maintain local SR information,
and receiving the other nodes' SR information through IGP protocol.
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They create the RIB and SR label forwarding table for traffic
forwarding. A centralized controller can be used to configure and
manage the nodes in the transport network. The segment routing nodes
report their topology information to the centralized controller, e.g.
through [I-D.ietf-idr-bgp-ls-segment-routing-ext]. The centralized
controller creates the RIB and synchronizes the forwarding table
among segment routing nodes. The centralized controller also
calculates the end to end SR paths, and creates the ordered segment
list, then downloads it to the ingress segment routing nodes.
Both the loose constraints path and strict constraints path are
support in the packet-switched transport networks. The SRTP loose
constraints path is usually used in the access rings or access and
aggregation rings for the east-west data flows (the synchronized data
among eNodeB) in the packet-switched transport, and the SRTP strict
constraints path is usually used for the south-north data flows
(e.g., the data from eNodeB to core network).
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************************
* *
* Controller *
* *
************************
/ ^
/ \
/ \
v \
+---+ +---+ +----+ +----+
|SR2|--------|SR3| |SR9 |-------|SR10|
+---+ +---+ +----+ +----+
/ \ / \
/ \ / \
+---+ +---+ +---+ +----+
|BS1|------|SR1| |SR4| |SR11|
+---+ +---+ +---+ +----+
| | |
| | |
+---+ +---+ +---+ +----+
|BS2|------|SR8| |SR5| |SR12|
+---+ +---+ +---+ +----+
\ / \ /
\ / \ /
+---+ +---+ +----+ +----+
|SR7|--------|SR6| |SR14|-------|SR13|
+---+ +---+ +----+ +----+
Figure 1 SRTP Scenario
4.2. SRTP Loose Constraints Path
Figure 2 shows the typical SRTP loose constraints path application
scenario. A and F is the ingress SR node and egress node
respectively, and D is the gateway of the access ring. The data
traffic will be forwarded to go across access ring and aggregation
ring from A to F. The F node's Node SID and D's Node SID are flooded
in the access ring and aggregation ring (The access ring and
aggregation ring belong to the same IGP area). Node A encapsulates
the SID D and SID F in the segment routing data packet. The data
traffic is forwarded along the best path from A to D, and then is
forwarded from D to F.
In the SRTP loose constraints path mechanism, the SR nodes in the IGP
area are assigned a global unique node SID, and all the SR nodes
should run IGP protocol(ISIS OR OSPF) to advertise their Node SIDs.
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The SR packets forwarding is based on the best route to the
destination SR nodes calculated at each node.
+-----------+ +-----------+
| B | | SR |
+-----------+ +-----------+
/ \ / \
/ \ / \
+-----+ +----+ +-----+
| A | | C | |SR11 |
+-----+ +----+ +-----+
| | |
| | |
+---+ +---+ +------+
|SR | | D | | F |
+---+ +---+ +------+
\ / \ /
\ / \ /
+-------------+ +------------+
| SR | | E |
+-------------+ +------------+
+--------+ +--------+
| node D | | node D |
+--------+ +--------+ +--------+ +--------+
| node E | | node E | | node E | | node E |
+--------+ +--------+ +--------+ +--------+ +--------+
|payload | |payload | |payload | |payload | |payload |
+--------+ +--------+ +--------+ +--------+ +--------+
Figure 2 SRTP Loose Constraints Path
4.3. SRTP Strict Constraints Path
Figure 3 shows the SRTP strict constraints path. The SR nodes are
assigned the Adjacent SIDs(local SID) by the centralized controller.
The centralized controller collects the global topology and TE
information, and calculates the end-to-end path based on the service
requirement and the routing policy (minimum hop count, minimum delay,
load balancing, etc.) to form the strictly constrained path. The
ingress SR nodes (PE nodes) push the SID list to encapsulate the SR
packet. The transit SR nodes (P nodes) forward the SR packets based
on the SID list. Egress SR nodes (PE nodes) decapsulate the SR
packet and forwards to the destination.
Because there is no label or only the last label in the MPLS label
stack when the packet reaches the egress node, the egress node cannot
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determine from which ingress node or SR path the packet comes. A
path segment is introduced to address this issue(Section 5 for
details).
+-----------+ +-----------+
| A | | SR |
+-----------+ +-----------+
/ \ / \
/ adj A adj B\ / \
+-----+ +----+ +-----+
| PE1 | | B | |SR11 |
+-----+ +----+ +-----+
| | |
| adj C | |
+---+ +---+ +-----+
|SR | | C | | PE2 |
+---+ +---+ +-----+
\ / \ adj D /
\ / \ / adj E
+-------------+ +------------+
| SR | | D |
+-------------+ +------------+
+--------+
| adj A |
+--------+ +--------+
| adj B | | adj B |
+--------+ +--------+ +--------+
| adj C | | adj C | | adj C |
+--------+ +--------+ +--------+
| adj D | | adj D | | adj D |
+--------+ +--------+ +--------+ +--------+
| adj E | | adj E | | adj E | | adj E |
+--------+ +--------+ +--------+ +--------+ +--------+
|path SID| |path SID| |path SID| |path SID| |path SID|
+--------+ +--------+ +--------+ +--------+ +--------+
|payload | |payload | |payload | |payload | |payload |
+--------+ +--------+ +--------+ +--------+ +--------+
Figure 3 SRTP Strict Constraints Path
5. Bi-direction SRTP Tunnel Binding
It is required to establish the bi-direction tunnel, for some use
cases, such as end-to-end 1+1 path protection, bidirectional path
correlation or performance measurement (PM) in MPLS-TP network . But
the SR is a one direction tunnel, so when deploying the SR to packet-
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switched transport networks, it is necessary to binding two direction
tunnel as a bi-direction tunnel to meet the requirement of MPLS-TP.
[I-D.cheng-spring-mpls-path-segment] provides the solution to binding
the bi-direction SRTP tunnel.
6. Security Considerations
7. Acknowledgements
8. IANA Considerations
9. Normative References
[I-D.cheng-spring-mpls-path-segment]
Cheng, W., Wang, L., Li, H., Chen, M., Zigler, R., and S.
Zhan, "Path Segment in MPLS Based Sement Routing Network",
draft-cheng-spring-mpls-path-segment-00 (work in
progress), October 2017.
[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-04
(work in progress), January 2018.
[I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura,
"IS-IS Extensions for Segment Routing", draft-ietf-isis-
segment-routing-extensions-15 (work in progress), December
2017.
[I-D.ietf-ospf-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", draft-ietf-ospf-segment-
routing-extensions-24 (work in progress), December 2017.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing
Architecture", draft-ietf-spring-segment-routing-15 (work
in progress), January 2018.
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[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-12
(work in progress), February 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>.
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
Sprecher, N., and S. Ueno, "Requirements of an MPLS
Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
September 2009, <https://www.rfc-editor.org/info/rfc5654>.
[RFC5921] Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
L., and L. Berger, "A Framework for MPLS in Transport
Networks", RFC 5921, DOI 10.17487/RFC5921, July 2010,
<https://www.rfc-editor.org/info/rfc5921>.
[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>.
Authors' Addresses
Fangwei Hu
ZTE Corporation
No.889 Bibo Rd
Shanghai 201203
China
Phone: +86 21 68896273
Email: hu.fangwei@zte.com.cn
Quan Xiong
ZTE Corporation
No.6 Huashi Park Rd
Wuhan, Hubei 430223
China
Phone: +86 27 83531060
Email: xiong.quan@zte.com.cn
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Greg Mirsky
ZTE Corporation
USA
Email: gregimirsky@gmail.com
Weiqiang Cheng
China Mobile
Beijing
China
Email: chengweiqiang@chinamobile.com
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