Network Working Group C. Filsfils, Ed.
Internet-Draft S. Previdi, Ed.
Intended status: Standards Track A. Bashandy
Expires: October 20, 2014 Cisco Systems, Inc.
B. Decraene
S. Litkowski
Orange
M. Horneffer
Deutsche Telekom
I. Milojevic
Telekom Srbija
R. Shakir
British Telecom
S. Ytti
TDC Oy
W. Henderickx
Alcatel-Lucent
J. Tantsura
Ericsson
E. Crabbe
Google, Inc.
April 18, 2014
Segment Routing with MPLS data plane
draft-filsfils-spring-segment-routing-mpls-01
Abstract
Segment Routing (SR) leverages the source routing paradigm. A node
steers a packet through a controlled set of instructions, called
segments, by prepending the packet with an SR header. A segment can
represent any instruction, topological or service-based. SR allows
to enforce a flow through any topological path and service chain
while maintaining per-flow state only at the ingress node to the SR
domain.
Segment Routing can be directly applied to the MPLS architecture with
no change in the forwarding plane. This drafts describes how Segment
Routing operates on top of the MPLS data plane.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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 October 20, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Illustration . . . . . . . . . . . . . . . . . . . . . . . . 3
3. MPLS Instantiation of Segment Routing . . . . . . . . . . . . 4
4. IGP Segments Examples . . . . . . . . . . . . . . . . . . . . 5
4.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . . . 7
4.4. Example 4 . . . . . . . . . . . . . . . . . . . . . . . . 7
4.5. Example 5 . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Segment List History . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Manageability Considerations . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
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10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The Segment Routing architecture [I-D.filsfils-rtgwg-segment-routing]
can be directly applied to the MPLS architecture with no change in
the MPLS forwarding plane. This drafts describes how Segment Routing
operates on top of the MPLS data plane.
The Segment Routing use cases are described in in
[I-D.filsfils-rtgwg-segment-routing-use-cases].
Link State protocol extensions for Segment Routing are described in
[I-D.previdi-isis-segment-routing-extensions],
[I-D.psenak-ospf-segment-routing-extensions] and
[I-D.psenak-ospf-segment-routing-ospfv3-extension].
2. Illustration
Segment Routing, applied to the MPLS data plane, offers the ability
to tunnel services (VPN, VPLS, VPWS) from an ingress PE to an egress
PE, without any other protocol than ISIS or OSPF
([I-D.previdi-isis-segment-routing-extensions] and
[I-D.psenak-ospf-segment-routing-extensions]). LDP and RSVP-TE
signaling protocols are not required.
Note that [draft-filsfils-rtgwg-segment-routing-ldp-interop-00]
documents SR co-existence and interworking with other MPLS signaling
protocols, if present in the network during a migration, or in case
of non-homogeneous deployments.
The operator only needs to allocate one node segment per PE and the
SR IGP control-plane automatically builds the required MPLS
forwarding constructs from any PE to any PE.
P1---P2
/ \
A---CE1---PE1 PE2---CE2---Z
\ /
P4---P4
Figure 1: IGP-based MPLS Tunneling
In Figure 1 above, the four nodes A, CE1, CE2 and Z are part of the
same VPN.
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PE2 advertises (in the IGP) a host address 192.0.2.2/32 with its
attached node segment 102.
CE2 advertises to PE2 a route to Z. PE2 binds a local label LZ to
that route and propagates the route and its label via MPBGP to PE1
with nhop 192.0.2.2 (PE2 loopback address).
PE1 installs the VPN prefix Z in the appropriate VRF and resolves the
next-hop onto the node segment 102. Upon receiving a packet from A
destined to Z, PE1 pushes two labels onto the packet: the top label
is 102, the bottom label is LZ. 102 identifies the node segment to
PE2 and hence transports the packet along the ECMP-aware shortest-
path to PE2. PE2 then processes the VPN label LZ and forwards the
packet to CE2.
Supporting MPLS services (VPN, VPLS, VPWS) with SR has the following
benefits:
Simple operation: one single intra-domain protocol to operate: the
IGP. No need to support IGP synchronization extensions as
described in [RFC5443] and [RFC6138].
Excellent scaling: one Node-SID per PE.
3. MPLS Instantiation of Segment Routing
When applied to MPLS, the 20 right-most bits of the segment are
encoded as a label. This implies that, in the MPLS instantiation,
the SID values are allocated within a reduced 20-bit space out of the
32-bit SID space.
The notion of indexed global segment fits the MPLS architecture
[RFC3031] as the absolute value allocated to any segment (global or
local) can be managed by a local allocation process (similarly to
other MPLS signaling protocols).
As described in [RFC3031] labels can be signaled by various
protocols. Within a SR domain, LDP and RSVP MPLS signaling protocols
are not required. If present, SR can coexist and interwork with LDP
and RSVP [draft-filsfils-rtgwg-segment-routing-ldp-interop-00].
The source routing model described in
[I-D.filsfils-rtgwg-segment-routing] is inherited from the ones
proposed by [RFC1940] and [RFC2460]. The source routing model offers
the support for explicit routing capability.
Contrary to RSVP-based explicit routes where tunnel midpoints
maintain states, SR-based explicit routes only require per-flow
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states at the ingress edge router where the traffic engineer policy
is applied.
Contrary to RSVP-based explicit routes which consist in non-ECMP
circuits (similar to ATM/FR), SR-based explicit routes can be built
as list of ECMP-aware node segments and hence ECMP-aware traffic
engineering is natively supported by SR.
When Segment Routing is instantiated over the MPLS data plane the
following applies:
A list of segments is represented as a stack of labels.
The active segment is the top label.
The CONTINUE operation is implemented as an MPLS swap operation.
When the same SRGB block is used throughout the SR domain, the
outgoing label value is equal to the incoming label value . Else,
the outgoing label value is [SRGB(next_hop)+index]
The NEXT operation is implemented as an MPLS pop operation.
The PUSH operation is implemented as an MPLS push of a label
stack.
In conclusion, there are no changes in the operations of the data-
plane currently used in MPLS networks.
4. IGP Segments Examples
Assuming the network diagram of Figure 2 and the IP address and IGP
Segment allocation of Figure 3, the following examples can be
constructed.
+--------+
/ \
R1-----R2----------R3-----R8
| \ / |
| +--R4--+ |
| |
+-----R5-----+
Figure 2: IGP Segments - Illustration
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+-----------------------------------------------------------+
| IP address allocated by the operator: |
| 192.0.2.1/32 as a loopback of R1 |
| 192.0.2.2/32 as a loopback of R2 |
| 192.0.2.3/32 as a loopback of R3 |
| 192.0.2.4/32 as a loopback of R4 |
| 192.0.2.5/32 as a loopback of R5 |
| 192.0.2.8/32 as a loopback of R8 |
| 198.51.100.9/32 as an anycast loopback of R4 |
| 198.51.100.9/32 as an anycast loopback of R5 |
| |
| SRGB defined by the operator as 1000-5000 |
| |
| Global IGP SID allocated by the operator: |
| 1001 allocated to 192.0.2.1/32 |
| 1002 allocated to 192.0.2.2/32 |
| 1003 allocated to 192.0.2.3/32 |
| 1004 allocated to 192.0.2.4/32 |
| 1008 allocated to 192.0.2.8/32 |
| 2009 allocated to 198.51.100.9/32 |
| |
| Local IGP SID allocated dynamically by R2 |
| for its "north" adjacency to R3: 9001 |
| for its "north" adjacency to R3: 9003 |
| for its "south" adjacency to R3: 9002 |
| for its "south" adjacency to R3: 9003 |
+-----------------------------------------------------------+
Figure 3: IGP Address and Segment Allocation - Illustration
4.1. Example 1
R1 may send a packet P1 to R8 simply by pushing an SR header with
segment list {1008}.
1008 is a global IGP segment attached to the IP prefix 192.0.2.8/32.
Its semantic is global within the IGP domain: any router forwards a
packet received with active segment 1008 to the next-hop along the
ECMP-aware shortest-path to the related prefix.
In conclusion, the path followed by P1 is R1-R2--R3-R8. The ECMP-
awareness ensures that the traffic be load-shared between any ECMP
path, in this case the two north and south links between R2 and R3.
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4.2. Example 2
R1 may send a packet P2 to R8 by pushing an SR header with segment
list {1002, 9001, 1008}.
1002 is a global IGP segment attached to the IP prefix 192.0.2.2/32.
Its semantic is global within the IGP domain: any router forwards a
packet received with active segment 1002 to the next-hop along the
shortest-path to the related prefix.
9001 is a local IGP segment attached by node R2 to its north link to
R3. Its semantic is local to node R2: R2 switches a packet received
with active segment 9001 towards the north link to R3.
In conclusion, the path followed by P2 is R1-R2-north-link-R3-R8.
4.3. Example 3
R1 may send a packet P3 along the same exact path as P1 using a
different segment list {1002, 9003, 1008}.
9003 is a local IGP segment attached by node R2 to both its north and
south links to R3. Its semantic is local to node R2: R2 switches a
packet received with active segment 9003 towards either the north or
south links to R3 (e.g. per-flow loadbalancing decision).
In conclusion, the path followed by P3 is R1-R2-any-link-R3-R8.
4.4. Example 4
R1 may send a packet P4 to R8 while avoiding the links between R2 and
R3 by pushing an SR header with segment list {1004, 1008}.
1004 is a global IGP segment attached to the IP prefix 192.0.2.4/32.
Its semantic is global within the IGP domain: any router forwards a
packet received with active segment 1004 to the next-hop along the
shortest-path to the related prefix.
In conclusion, the path followed by P4 is R1-R2-R4-R3-R8.
4.5. Example 5
R1 may send a packet P5 to R8 while avoiding the links between R2 and
R3 while still benefitting from all the remaining shortest paths (via
R4 and R5) by pushing an SR header with segment list {2009, 1008}.
2009 is a global IGP segment attached to the anycast IP prefix
198.51.100.9/32. Its semantic is global within the IGP domain: any
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router forwards a packet received with active segment 2009 to the
next-hop along the shortest-path to the related prefix.
In conclusion, the path followed by P5 is either R1-R2-R4-R3-R8 or
R1-R2-R5-R3-R8 .
5. Segment List History
In the abstract SR routing model
[I-D.filsfils-rtgwg-segment-routing], any node N along the journey of
the packet is able to determine where the packet P entered the SR
domain and where it will exit. The intermediate node is also able to
determine the paths from the ingress edge router to itself, and from
itself to the egress edge router.
In the MPLS instantiation, as the packet travels through the SR
domain, the stack is depleted and the segment list history is
gradually lost.
Future version of this document will describe how this information
can be preserved in MPLS domains.
6. IANA Considerations
TBD
7. Manageability Considerations
TBD
8. Security Considerations
TBD
9. Acknowledgements
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
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10.2. Informative References
[I-D.filsfils-rtgwg-segment-routing-use-cases]
Filsfils, C., Francois, P., Previdi, S., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., Kini, S., and E.
Crabbe, "Segment Routing Use Cases", draft-filsfils-rtgwg-
segment-routing-use-cases-02 (work in progress), October
2013.
[I-D.filsfils-rtgwg-segment-routing]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
"Segment Routing Architecture", draft-filsfils-rtgwg-
segment-routing-01 (work in progress), October 2013.
[I-D.previdi-isis-segment-routing-extensions]
Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
Litkowski, S., and J. Tantsura, "IS-IS Extensions for
Segment Routing", draft-previdi-isis-segment-routing-
extensions-05 (work in progress), February 2014.
[I-D.psenak-ospf-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., and W. Henderickx, "OSPF Extensions for
Segment Routing", draft-psenak-ospf-segment-routing-
extensions-04 (work in progress), February 2014.
[I-D.psenak-ospf-segment-routing-ospfv3-extension]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., and W. Henderickx, "OSPFv3 Extensions for
Segment Routing", draft-psenak-ospf-segment-routing-
ospfv3-extension-01 (work in progress), February 2014.
[RFC1940] Estrin, D., Li, T., Rekhter, Y., Varadhan, K., and D.
Zappala, "Source Demand Routing: Packet Format and
Forwarding Specification (Version 1)", RFC 1940, May 1996.
[RFC5443] Jork, M., Atlas, A., and L. Fang, "LDP IGP
Synchronization", RFC 5443, March 2009.
[RFC6138] Kini, S. and W. Lu, "LDP IGP Synchronization for Broadcast
Networks", RFC 6138, February 2011.
[draft-filsfils-rtgwg-segment-routing-ldp-interop-00]
Filsfils, C. and S. Previdi, "Segment Routing
interoperability with LDP", October 2013.
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Authors' Addresses
Clarence Filsfils (editor)
Cisco Systems, Inc.
Brussels
BE
Email: cfilsfil@cisco.com
Stefano Previdi (editor)
Cisco Systems, Inc.
Via Del Serafico, 200
Rome 00142
Italy
Email: sprevidi@cisco.com
Ahmed Bashandy
Cisco Systems, Inc.
170, West Tasman Drive
San Jose, CA 95134
US
Email: bashandy@cisco.com
Bruno Decraene
Orange
FR
Email: bruno.decraene@orange.com
Stephane Litkowski
Orange
FR
Email: stephane.litkowski@orange.com
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Martin Horneffer
Deutsche Telekom
Hammer Str. 216-226
Muenster 48153
DE
Email: Martin.Horneffer@telekom.de
Igor Milojevic
Telekom Srbija
Takovska 2
Belgrade
RS
Email: igormilojevic@telekom.rs
Rob Shakir
British Telecom
London
UK
Email: rob.shakir@bt.com
Saku Ytti
TDC Oy
Mechelininkatu 1a
TDC 00094
FI
Email: saku@ytti.fi
Wim Henderickx
Alcatel-Lucent
Copernicuslaan 50
Antwerp 2018
BE
Email: wim.henderickx@alcatel-lucent.com
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Jeff Tantsura
Ericsson
300 Holger Way
San Jose, CA 95134
US
Email: Jeff.Tantsura@ericsson.com
Edward Crabbe
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: edc@google.com
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