SR Replication Segment for Multi-point Service Delivery
draft-ietf-spring-sr-replication-segment-08
The information below is for an old version of the document.
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|---|---|---|---|
| Authors | Daniel Voyer , Clarence Filsfils , Rishabh Parekh , Hooman Bidgoli , Zhaohui (Jeffrey) Zhang | ||
| Last updated | 2022-07-01 | ||
| Replaces | draft-voyer-spring-sr-replication-segment | ||
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draft-ietf-spring-sr-replication-segment-08
Network Working Group D. Voyer, Ed.
Internet-Draft Bell Canada
Intended status: Standards Track C. Filsfils
Expires: 2 January 2023 R. Parekh
Cisco Systems, Inc.
H. Bidgoli
Nokia
Z. Zhang
Juniper Networks
1 July 2022
SR Replication Segment for Multi-point Service Delivery
draft-ietf-spring-sr-replication-segment-08
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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 2 January 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Replication Segment . . . . . . . . . . . . . . . . . . . . . 3
2.1. SR-MPLS data plane . . . . . . . . . . . . . . . . . . . 4
2.2. SRv6 data plane . . . . . . . . . . . . . . . . . . . . . 5
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Illustration of a Replication Segment . . . . . . . 9
A.1. SR-MPLS . . . . . . . . . . . . . . . . . . . . . . . . . 9
A.2. SRv6 . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
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-Multipoint Service
delivery via SR Point-to-Multipoint (SR P2MP) policy. A Replication
segment can replicate packet to directly connected nodes or to
downstream nodes (without need for state on the transit routers).
This document focuses on the Replication segment building block. The
use of one or more stitched Replication segments constructed for SR
P2MP Policy tree is specified in [I-D.ietf-pim-sr-p2mp-policy].
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2. Replication Segment
In a Segment Routing Domain, a Replication segment is a logical
construct which connects a Replication Node to a set of Downstream
Nodes. A Replication segment is a local segment instantiated at a
Replication node. It can be either provisioned locally on a 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:
* Replication-ID: An identifier for a Replication segment that is
unique in context of the Replication Node.
* 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.ietf-pim-sr-p2mp-policy].
A Replication segment includes the following elements:
* Replication SID: The Segment Identifier of a Replication segment.
This is a SR-MPLS label or a SRv6 SID [RFC8402].
* Downstream Nodes: Set of nodes in Segment Routing domain to which
a packet is replicated by the Replication segment.
* 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 SID identifies the Replication segment in the forwarding
plane. At a Replication node, the Replication SID is the equivalent
of Binding SID [I-D.ietf-spring-segment-routing-policy] of a Segment
Routing Policy.
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.
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In a branch tuple, <Downstream Node> represents the reachability from
the Replication Node to the Downstream Node. In its simplest form,
this MAY be specified as an interface or nexthop if downstream node
is adjacent to the Replication Node. The reachability may be
specified in terms of Flex-Algo path (including the default algo)
[I-D.ietf-lsr-flex-algo], or specified by an SR explicit path
represented either by a SID-list (of one or more SIDs) or by a
Segment Routing Policy [I-D.ietf-spring-segment-routing-policy].
A packet is steered into a Replication segment at a Replication Node
in two ways:
* When the Active Segment [RFC8402] is a locally instantiated
Replication SID
* By the root of a multi-point service based on local configuration
outside the scope of this document.
In either case, the packet is replicated to each Downstream node in
the associated Replication state.
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. At an egress node, the Replication SID MAY be
used to identify that portion of the multi-point service. 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.ietf-pim-sr-p2mp-policy].
2.1. SR-MPLS data plane
When the Active Segment is a Replication SID, the processing results
in a POP operation and lookup of the associated Replication state.
For each replication in the Replication state, the operation is a
PUSH of the downstream Replication SID and an optional segment list
on to the packet which is forwarded to the Downstream node. For leaf
nodes the inner packet is forwarded as per local configuration.
When the root of a multi-point service steers a packet to a
Replication segment, it results in a replication to each Downstream
node in the associated replication state. The operation is a PUSH of
the replication SID and an optional segment list on to the packet
which is forwarded to the downstream node.
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2.2. SRv6 data plane
In SRv6 [RFC8986], the "Endpoint with replication" behavior
(End.Replicate for short) replicates a packet and forwards the packet
according to a Replication state.
When processing a packet destined to a local Replication-SID, the
packet is replicated to Downstream nodes and/or locally delivered off
tree (when this is a bud/leaf node) according to the associated
replication state. For replication, the outer header is re-used, and
the Downstream Replication SID is written into the outer IPv6 header
destination address. If required, an optional segment list may be
used on some branches using H.Encaps.Red (while some other branches
may not need that). Note that this H.Encaps.Red is independent from
the replication segment - it is just used to steer the replicated
traffic on a traffic engineered path to a Downstream node. If SRv6
SID compression is possible [I-D.ietf-spring-srv6-srh-compression],
the Replication node SHOULD use a CSID container with Downstream
Replication SID as the Last uSID in the container instead of
H.Encaps.Red.
The above also applies when the Replication segment is for the Root
node, whose upstream node has placed the Replication-SID in the
header. A local application (e.g. MVPN/EVPN) may also apply
H.Encaps.Red and then steer the resulting traffic into the segment.
Again note that the H.Encaps.Red is independent of the Replication
segment - it is the action of the application (e.g. MVPN/EVPN
service). If the service is on a Root node, the two H.Encaps
mentioned, one for the service and other in the previous paragraph
for replication to Downstream node SHOULD be combined for
optimization (to avoid extra IPv6 encapsulation).
For the local delivery on a bud/leaf node, the action associated with
Replication-SID is "look at next SID in SRH". The next SID could be
a SID with End.DTMC4/6 or End.DT2M local behavior (equivalent of
MVPN/EVPN PMSI label in case of tunnel sharing across multiple VPNs).
There may also not be a next SID (e.g. MVPN/EVPN with one tunnel per
VPN), in which case the Replication-SID is then equivalent to
End.DTM4/6 or End.DT2M. Note that decapsulation is not an inherent
action of a Replication segment even on a bud/leaf node.
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
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.
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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 replication. That is specified in
[I-D.ietf-pim-sr-p2mp-policy].
4. IANA Considerations
This document requests IANA to allocate the following codepoints in
"SRv6 Endpoint Behaviors" sub-registry of "Segment Routing
Parameters" top-level registry.
+=======+========+===================+===========+
| Value | Hex | Endpoint behavior | Reference |
+=======+========+===================+===========+
| 75 | 0x004B | End.Replicate | [This.ID] |
+-------+--------+-------------------+-----------+
Table 1: IETF - SRv6 Endpoint Behaviors
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, Alexander Vainshtein, Bruno Decraene, Thierry
Couture and Joel Halpern 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
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Swadesh Agrawal Cisco Systems, Inc. San Jose US
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
Andrew Stone Nokia Ottawa Canada
Email: andrew.stone@nokia.com
Tarek Saad Juniper Networks Canada
Email:tsaad@juniper.net
Kamran Raza Cisco Systems, Inc. Canada
Email:skraza@cisco.com
8. References
8.1. Normative References
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", Work in
Progress, Internet-Draft, draft-ietf-spring-segment-
routing-policy-22, 22 March 2022,
<https://www.ietf.org/archive/id/draft-ietf-spring-
segment-routing-policy-22.txt>.
[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>.
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[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
8.2. Informative References
[I-D.filsfils-spring-srv6-net-pgm-illustration]
Filsfils, C., Garvia, P. C., Li, Z., Matsushima, S.,
Decraene, B., Steinberg, D., Lebrun, D., Raszuk, R., and
J. Leddy, "Illustrations for SRv6 Network Programming",
Work in Progress, Internet-Draft, draft-filsfils-spring-
srv6-net-pgm-illustration-04, 30 March 2021,
<https://www.ietf.org/archive/id/draft-filsfils-spring-
srv6-net-pgm-illustration-04.txt>.
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", Work in Progress,
Internet-Draft, draft-ietf-lsr-flex-algo-20, 18 May 2022,
<https://www.ietf.org/archive/id/draft-ietf-lsr-flex-algo-
20.txt>.
[I-D.ietf-pim-sr-p2mp-policy]
(editor), D. V., Filsfils, C., Parekh, R., Bidgoli, H.,
and Z. Zhang, "Segment Routing Point-to-Multipoint
Policy", Work in Progress, Internet-Draft, draft-ietf-pim-
sr-p2mp-policy-04, 7 March 2022,
<https://www.ietf.org/archive/id/draft-ietf-pim-sr-p2mp-
policy-04.txt>.
[I-D.ietf-spring-srv6-srh-compression]
Cheng, W., Filsfils, C., Li, Z., Decraene, B., Cai, D.,
Voyer, D., Clad, F., Zadok, S., Guichard, J. N., Aihua,
L., Raszuk, R., and C. Li, "Compressed SRv6 Segment List
Encoding in SRH", Work in Progress, Internet-Draft, draft-
ietf-spring-srv6-srh-compression-01, 21 March 2022,
<https://www.ietf.org/archive/id/draft-ietf-spring-srv6-
srh-compression-01.txt>.
[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>.
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[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>.
Appendix A. Illustration of a Replication Segment
This section illustrates an example of a single Replication segment.
Examples showing Replication segment stitched together to form P2MP
tree (based on SR P2MP policy) are in [I-D.ietf-pim-sr-p2mp-policy].
Consider the following topology:
R3------R6
/ \
R1----R2----R5-----R7
\ /
+--R4---+
Figure 1: Figure 1
A.1. SR-MPLS
In this example, the Node-SID of a node Rn is N-SIDn and Adjacency-
SID from node Rm to node Rn is A-SIDmn. Interface between Rm and Rn
is Lmn.
Assume a Replication segment identified with R-ID at Replication Node
R1 and downstream Nodes R2, R6 and R7. The Replication SID at node n
is R-SIDn. A packet replicated from R1 to R7 has to traverse R4.
The Replication segment state at nodes R1, R2, R6 and R7 is shown
below. Note nodes R3, R4 and R5 do not have state for the
Replication segment.
Replication segment at R1:
Replication segment <R-ID,R1>:
Replication SID: R-SID1
Replication State:
R2: <R-SID2->L12>
R6: <N-SID6, R-SID6>
R7: <N-SID4, A-SID47, R-SID7>
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Replication to R2 steers packet directly to R2 on interface L12.
Replication to R6, using N-SID6, steers packet via IGP shortest path
to that node. Replication to R7 is steered via R4, using N-SID4 and
then adjacency SID A-sID47 to R7.
Replication segment at R2:
Replication segment <R-ID,R2>:
Replication SID: R-SID2
Replication State:
R2: <Leaf>
Replication segment at R6:
Replication segment <R-ID,R6>:
Replication SID: R-SID6
Replication State:
R6: <Leaf>
Replication segment at R7:
Replication segment <R-ID,R7>:
Replication SID: R-SID7
Replication State:
R7: <Leaf>
When a packet is steered into the Replication segment at R1:
* Since R1 is directly connected to R2, R1 performs PUSH operation
with just <R-SID2> label for the replicated copy and sends it to
R2 on interface L12. R2, as Leaf, performs NEXT operation, pops
R-SID2 label and delivers the payload.
* R1 performs PUSH operation with <N-SID6, R-SID6> label stack for
the replicated copy to R6 and sends it to R2, the nexthop on IGP
shortest path to R6. R2 performs CONTINUE operation on N-SID6 and
forwards it to R3. R3 is the penultimate hop for N-SID6; it
performs penultimate hop popping, which corresponds to the NEXT
operation and the packet is then sent to R6 with <R-SID6> in the
label stack. R6, as Leaf, performs NEXT operation, pops R-SID6
label and delivers the payload.
* R1 performs PUSH operation with <N-SID4, A-SID47, R-SID7> label
stack for the replicated copy to R7 and sends it to R2, the
nexthop on IGP shortest path to R4. R2 is the penultimate hop for
N-SID4; it performs penultimate hop popping, which corresponds to
the NEXT operation and the packet is then sent to R4 with
<A-SID47, R-SID1> in the label stack. R4 performs NEXT operation,
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pops A-SID47, and delivers packet to R7 with <R-SID7> in the label
stack. R7, as Leaf, performs NEXT operation, pops R-SID7 label
and delivers the payload.
A.2. SRv6
For SRv6 , we use SID allocation scheme, reproduced below, from
Illustrations for SRv6 Network Programming
[I-D.filsfils-spring-srv6-net-pgm-illustration]
* 2001:db8::/32 is an IPv6 block allocated by a RIR to the operator
* 2001:db8:0::/48 is dedicated to the internal address space
* 2001:db8:cccc::/48 is dedicated to the internal SRv6 SID space
* We assume a location expressed in 64 bits and a function expressed
in 16 bits
* Node k has a classic IPv6 loopback address 2001:db8::k/128 which
is advertised in the IGP
* Node k has 2001:db8:cccc:k::/64 for its local SID space. Its SIDs
will be explicitly assigned from that block
* Node k advertises 2001:db8:cccc:k::/64 in its IGP
* Function :1:: (function 1, for short) represents the End function
with PSP support
* Function :Cn:: (function Cn, for short) represents the End.X
function from to Node n
Each node k has:
* An explicit SID instantiation 2001:db8:cccc:k:1::/128 bound to an
End function with additional support for PSP
* An explicit SID instantiation 2001:db8:cccc:k:Cj::/128 bound to an
End.X function to neighbor J with additional support for PSP
* An explicit SID instantiation 2001:db8:cccc:k:Fk::/128 bound to an
End.Replcate function
Assume a Replication segment identified with R-ID at Replication Node
R1 and downstream Nodes R2, R6 and R7. The Replication SID at node
k, bound to an End.Replcate function, is 2001:db8:cccc:k:Fk::/128. A
packet replicated from R1 to R7 has to traverse R4.
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The Replication segment state at nodes R1, R2, R6 and R7 is shown
below. Note nodes R3, R4 and R5 do not have state for the
Replication segment.
Replication segment at R1:
Replication segment <R-ID,R1>:
Replication SID: 2001:db8:cccc:1:F1::0
Replication State:
R2: <2001:db8:cccc:2:F2::0->L12>
R6: <2001:db8:cccc:6:F6::0>
R7: <2001:db8:cccc:4:C7::0, 2001:db8:cccc:7:F7::0>
Replication to R2 steers packet directly to R2 on interface L12.
Replication to R6, using 2001:db8:cccc:6:F6::0, steers packet via IGP
shortest path to that node. Replication to R7 is steered via R4,
using End.X SID 2001:db8:cccc:4:C7::0 at R4 to R7.
Replication segment at R2:
Replication segment <R-ID,R2>:
Replication SID: 2001:db8:cccc:2:F2::0
Replication State:
R2: <Leaf>
Replication segment at R6:
Replication segment <R-ID,R6>:
Replication SID: 2001:db8:cccc:6:F6::0
Replication State:
R6: <Leaf>
Replication segment at R7:
Replication segment <R-ID,R7>:
Replication SID: 2001:db8:cccc:7:F7::0
Replication State:
R7: <Leaf>
When a packet, (A,B2), is steered into the Replication segment at R1:
* Since R1 is directly connected to R2, R1 creates encapsulated
replicated copy (2001:db8::1, 2001:db8:cccc:2:F2::0) (A, B2), and
sends it to R2 on interface L12. R2, as Leaf, removes outer IPv6
header and delivers the payload.
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* R1 creates encapsulated replicated copy (2001:db8::1,
2001:db8:cccc:6:F6::0) (A, B2) then forwards the resulting packet
on the shortest path to 2001:db8:cccc:6::/64. R2 and R3 forward
the packet using 2001:db8:cccc:6::/64. R6, as Leaf, removes outer
IPv6 header and delivers the payload.
* R1 creates encapsulated replicated copy (2001:db8::1,
2001:db8:cccc:4:C7::0) (2001:db8:cccc:7:F7::0; SL=1) (A, B2) and
sends it to R2, the nexthop on IGP shortest path to
2001:db8:cccc:4::/64. R2 forwards packet to R4 using
2001:db8:cccc:4::/64. R4 executes End.X function on
2001:db8:cccc:4:C7::0, performs PSP action, removes SRH and sends
resulting packet (2001:db8::1, 2001:db8:cccc:7:F7::0) (A, B2) to
R7. R7, as Leaf, removes outer IPv6 header and delivers the
payload.
Authors' Addresses
Daniel Voyer (editor)
Bell Canada
Montreal
Canada
Email: daniel.voyer@bell.ca
Clarence Filsfils
Cisco Systems, Inc.
Brussels
Belgium
Email: cfilsfil@cisco.com
Rishabh Parekh
Cisco Systems, Inc.
San Jose,
United States of America
Email: riparekh@cisco.com
Hooman Bidgoli
Nokia
Ottawa
Canada
Email: hooman.bidgoli@nokia.com
Zhaohui Zhang
Juniper Networks
Voyer, Ed., et al. Expires 2 January 2023 [Page 13]
Internet-Draft SR Replication Segment July 2022
Email: zzhang@juniper.net
Voyer, Ed., et al. Expires 2 January 2023 [Page 14]