Network Working Group D. Voyer, Ed.
Internet-Draft Bell Canada
Intended status: Standards Track C. Filsfils
Expires: December 3, 2020 R. Parekh
Cisco Systems, Inc.
H. Bidgoli
Nokia
Z. Zhang
Juniper Networks
June 1, 2020
SR Replication Segment for Multi-point Service Delivery
draft-voyer-spring-sr-replication-segment-03
Abstract
This document describes the SR Replication segment for Multi-point
service delivery. A SR Replication segment allows a packet to be
replicated from a replication node to downstream nodes.
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].
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
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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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 3, 2020.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Replication Segment . . . . . . . . . . . . . . . . . . . . . 2
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
We define a new type of segment for Segment Routing [RFC8402], called
Replication segment, which allows a node (henceforth called as
Replication Node) to replicate packets to a set of other nodes
(called Downstream Nodes) in a Segment Routing Domain. Replication
segments provide building blocks for Point-to-Multi-point Service
delivery. A Replication segment at ingress node of Multi-point
service could replicates packets directly to each egress node of the
service (without need for any state on the internal routers), or it
could be stitched to other Replication segments to build a tree in SR
domain for Multi-point service. The latter is outside the scope of
this document but specified in [I-D.voyer-pim-sr-p2mp-policy].
2. Replication Segment
In a Segment Routing Domain, a Replication segment is a logical
segment which connects a Replication Node to a set of Downstream
Nodes. A Replication segment can be either provisioned locally on a
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node or programmed by a PCE. Replication segments apply equally to
both SR-MPLS and SRv6 instantiations of Segment Routing.
A Replication segment is identified by the tuple <Replication-ID,
Node-ID>, where:
o Replication-ID: An identifier for a Replication segment that is
unique in context of the Replication Node.
o Node-ID: The address of the Replication Node that the Replication
segment is for. Note that the root of a Multi-point service is
also a replication node.
In simplest case, Replication-ID can be a 32-bit number, but it can
be extended or modified as required based on specific use of a
Replication segment. When the PCE signals a Replication segment to
its node, the <Replication-ID, Node-ID> tuple identifies the segment.
Examples of such signaling and extension are described in
[I-D.voyer-pim-sr-p2mp-policy].
A Replication segment includes the following elements:
o Replication SID: The Segment Identifier of a Replication segment.
This is a SR-MPLS label or a SRv6 SID [RFC8402].
o Downstream Nodes: Set of nodes in Segment Routing domain to which
a packet is replicated by the Replication segment.
o Replication State: See below.
The Downstream Nodes and Replication State of a Replication segment
can change over time, depending on the network state and leaf nodes
of a Multi-point service that the segment is part of.
Replication State is a list of replication branches to the Downstream
Nodes. In this document, each branch is abstracted to a <Downstream
Node, Downstream Replication SID> tuple. A Downstream Node could be
represented by the node's Node SID (i.e. it does not matter how
traffic gets to the Downstream Node, whether it's directly connected
or not), or in case of a directly connected node it could be
represented by the Adjacency SID (for the interface connecting to the
directly connected Leaf Node). Alternatively, a Downstream Node
could be represented by a SID-list or a Segment Routing Policy
[I-D.ietf-spring-segment-routing-policy] that partially/fully
specifies the explicit path from the Replication Node to the
Downstream Node, or even represented by another Replication segment.
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Replication SID identifies the Replication segment in the forwarding
plane. For the root of a Multi-point service, the Replication SID
SHOULD be considered to be the equivalent of Binding SID
[I-D.ietf-spring-segment-routing-policy] of a Segment Routing Policy.
At a downstream node of the Multi-point service, the Replication SID
MAY be used to identify that portion of the Multi-point service.
A packet steered into a Replication segment at a node is replicated
to each Downstream Node with the Downstream Replication SID that is
relevant at that node. A packet is steered into a Replication
Segment in two ways:
o When the Active Segment [RFC8402] is the Replication SID. In this
case, the operation for a replicated copy is CONTINUE.
o On the root of a Multi-point service, based on local policy-based
routing. In this case, the operation for a replicated copy is
PUSH.
If a Downstream Node is an egress (aka leaf) of the Multi-point
service, i.e. no further replication is needed, then that leaf node's
Replication segment will not have any Replication State and the
operation is NEXT. Notice that the segment on the leaf node is still
referred to as a Replication segment for the purpose of
generalization.
A node can be a bud node, i.e. it is a replication node and a leaf
node of a Multi-point service at the same time
[I-D.voyer-pim-sr-p2mp-policy]. In this case, the Replication
segment's Replication State includes a branch with the Downstream
Node being itself and the operation for the replicated copy is NEXT.
3. Use Cases
In the simplest use case, a single Replication segment includes the
root node of a Multi-point service and the egress/leaf nodes of the
the service as all the Downstream Nodes. This achieves Ingress
Replication [RFC7988] that has been widely used for MVPN [RFC6513]
and EVPN [RFC7432] BUM (Broadcast, Unknown and Multicast) traffic.
Replication segments can also be used as building blocks for
replication trees when Replication segments on the root, intermediate
replication nodes and leaf nodes are stitched together to achieve
efficient replciation. That is specified in
[I-D.voyer-pim-sr-p2mp-policy].
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4. IANA Considerations
This document makes no request of IANA.
5. Security Considerations
There are no additional security risks introduced by this design.
6. Acknowledgements
The authors would like to acknowledge Siva Sivabalan, Mike Koldychev,
Vishnu Pavan Beeram and Alexander Vainshtein for their valuable
inputs.
7. Contributors
Clayton Hassen
Bell Canada
Vancouver
Canada
Email: clayton.hassen@bell.ca
Kurtis Gillis
Bell Canada
Halifax
Canada
Email: kurtis.gillis@bell.ca
Arvind Venkateswaran
Cisco Systems, Inc.
San Jose
US
Email: arvvenka@cisco.com
Zafar Ali
Cisco Systems, Inc.
US
Email: zali@cisco.com
Swadesh Agrawal
Cisco Systems, Inc.
San Jose
US
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Email: swaagraw@cisco.com
Jayant Kotalwar
Nokia
Mountain View
US
Email: jayant.kotalwar@nokia.com
Tanmoy Kundu
Nokia
Mountain View
US
Email: tanmoy.kundu@nokia.com
Tarek Saad
Juniper Networks
Canada
Email:tsaad@juniper.net
8. References
8.1. Normative References
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-07 (work in progress),
May 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>.
[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>.
8.2. Informative References
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[I-D.voyer-pim-sr-p2mp-policy]
Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z.
Zhang, "Segment Routing Point-to-Multipoint Policy",
draft-voyer-pim-sr-p2mp-policy-01 (work in progress),
April 2020.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <https://www.rfc-editor.org/info/rfc6513>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
[RFC7988] Rosen, E., Ed., Subramanian, K., and Z. Zhang, "Ingress
Replication Tunnels in Multicast VPN", RFC 7988,
DOI 10.17487/RFC7988, October 2016,
<https://www.rfc-editor.org/info/rfc7988>.
Authors' Addresses
Daniel Voyer (editor)
Bell Canada
Montreal
CA
Email: daniel.voyer@bell.ca
Clarence Filsfils
Cisco Systems, Inc.
Brussels
BE
Email: cfilsfil@cisco.com
Rishabh Parekh
Cisco Systems, Inc.
San Jose
US
Email: riparekh@cisco.com
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Hooman Bidgoli
Nokia
Ottawa
CA
Email: hooman.bidgoli@nokia.com
Zhaohui Zhang
Juniper Networks
Email: zzhang@juniper.net
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