Internet DRAFT - draft-ietf-bess-mvpn-evpn-sr-p2mp
draft-ietf-bess-mvpn-evpn-sr-p2mp
Network Working Group R. Parekh
Internet-Draft C. Filsfils
Intended status: Standards Track A. Venkateswaran
Expires: 9 May 2024 Cisco Systems, Inc.
H. Bidgoli
Nokia
D. Voyer
Bell Canada
Z. Zhang
Juniper Networks
6 November 2023
Multicast and Ethernet VPN with Segment Routing P2MP and Ingress
Replication
draft-ietf-bess-mvpn-evpn-sr-p2mp-08
Abstract
A Point-to-Multipoint (P2MP) Tree in a Segment Routing domain carries
traffic from a Root to a set of Leaves. This document describes
extensions to BGP encodings and procedures for P2MP trees and Ingress
Replication used in BGP/MPLS IP VPNs and Ethernet VPNs in a Segment
Routing domain.
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 9 May 2024.
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Copyright Notice
Copyright (c) 2023 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
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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. SR P2MP P-Tunnels . . . . . . . . . . . . . . . . . . . . . . 3
3. PMSI Tunnel Attribute for SR P2MP . . . . . . . . . . . . . . 4
3.1. MPLS Label . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.1. SR-MPLS . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.2. SRv6 . . . . . . . . . . . . . . . . . . . . . . . . 5
4. MVPN Auto-Discovery and Binding Procedures for P2MP Trees . . 6
4.1. Intra-AS I-PMSI . . . . . . . . . . . . . . . . . . . . . 7
4.1.1. Originating Intra-AS I-PMSI routes . . . . . . . . . 7
4.1.2. Receiving Intra-AS I-PMSI A-D routes . . . . . . . . 7
4.2. Using S-PMSIs for binding customer flows to P2MP
Segments . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2.1. Originating S-PMSI A-D routes . . . . . . . . . . . . 8
4.2.2. Receiving S-PMSI A-D routes . . . . . . . . . . . . . 9
4.3. Inter-AS P-tunnels using P2MP Segments . . . . . . . . . 10
4.3.1. Advertising Inter-AS I-PMSI routes into iBGP . . . . 10
4.3.2. Receiving Inter-AS I-PMSI A-D routes in iBGP . . . . 10
4.4. Leaf A-D routes for P2MP Segment Leaf Discovery . . . . . 10
4.4.1. Originating Leaf A-D routes . . . . . . . . . . . . . 10
4.4.2. Receiving Leaf A-D routes . . . . . . . . . . . . . . 11
5. MVPN with Ingress Replication over Segment Routing . . . . . 11
5.1. SR-MPLS . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2. SRv6 . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2.1. SRv6 Multicast Endpoint Behaviors . . . . . . . . . . 14
6. Dampening of MVPN routes . . . . . . . . . . . . . . . . . . 14
7. SR P2MP Trees for EVPN . . . . . . . . . . . . . . . . . . . 15
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
12.1. Normative References . . . . . . . . . . . . . . . . . . 17
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12.2. Informative References . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
Multicast in MPLS/BGP IP VPNs [RFC6513] and BGP Encodings and
Procedures for Multicast in MPLS/BGP IP VPNs [RFC6514] specify
procedures that allow a Service Provider to provide Multicast VPN
(MVPN) service to its customers. Multicast traffic from a customer
is tunneled across the service provider network over Provider Tunnels
(P-Tunnels). P-Tunnels can be instantiated via different
technologies. A service provider network that uses Segment Routing
can use a Point-to-Multipoint (SR P2MP) tree
[I-D.ietf-pim-sr-p2mp-policy] or P2MP Ingress Replication to
instantiate P-Tunnels for MVPN. SR P2MP P-Tunnels can be realized
both for SR-MPLS [RFC8660] and SRv6 [RFC8986][RFC8754].
In a Segment Routing network, a P2MP tree allows efficient delivery
of traffic from a Root to set of Leaf nodes. A SR P2MP tree is
defined by a SR P2MP Policy and instantiated via a PCE. A P2MP
Policy consists of a Root, a Set of Leaf Nodes and a set of candidate
paths with optional set of constraints and/or optimization objectives
to be satisfied by the P2MP tree. A unique Identifier, called Tree-
SID, is associated with a P2MP tree. This Tree-SID can be an MPLS
label or an IPv6 address.
This document describes extensions to BGP Auto-Discovery procedures
specified in RFC 6514 for SR P2MP P-Tunnels. Use of PIM for Auto-
Discovery is outside scope of this document. Support for customer
BIDIR-PIM is outside the scope of this document.
For BGP MPLS Ethernet VPN specified in [RFC7432] and extensions to
this document, P-Tunnels are advertised for handling multi-
destination traffic. These P-Tunnels can be realized by SR-MPLS or
SRv6 P2MP trees. SRv6 P2MP trees can also be used to support
Multicast in Network Virtualization over Layer 3 [RFC8293].
The reader is expected to be familiar with concepts and terminology
of RFC 6513, RFC 6514 and SR P2MP drafts.
2. SR P2MP P-Tunnels
For MVPN or EVPN, Provider Edge(PE) routers steer customer traffic
into a P-Tunnel that can be instantiated by a SR-MPLS or SRv6 P2MP.
A SR P2MP tree is defined by a SR P2MP policy
[I-D.ietf-pim-sr-p2mp-policy].
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Given a SR P2MP policy, a PCE computes and instantiates the SR P2MP
tree on the nodes that are part of the tree by stitching Replication
segments [I-D.ietf-spring-sr-replication-segment] at Root, Leaf and
intermediate replication nodes. Tree-SID is an unique identifier for
the tree. A Replication segment of a SR P2MP tree can be initiated
by various methods (BGP, PCEP, others) which are outside the scope of
this document.
A PCE provides conceptual APIs, listed below, to define and modify SR
P2MP policies SR P2MP Policy Section 4.1.1
(https://tools.ietf.org/html/draft-ietf-pim-sr-p2mp-policy-
00#section-4.1.1). These APIs are invoked by a PCC, which is the
root of P2MP tree, using various methods (BGP, PCEP, etc.) which are
outside the scope of this document.
CreatePolicy: CreateSRP2MPPolicy<Root, Tree-ID>
DeletePolicy: DeleteSRP2MPPolicy<Root, Tree-ID>
UpdateLeafSet: SRP2MPPolicyLeafSetModify<Root, Tree-ID, {Leaf
Set}>
The Root of a P2MP tree imposes the Tree-SID to steer the customer
payload into the P2MP tree. Provider (P) routers replicate customer
payload, using Replication segments, towards the Leaf nodes of the
P2MP tree. Leaf nodes of the P2MP tree deliver the customer payload
after disposing the Tree-SID.
An Ingress PE can deliver payload to egress PEs of the service using
Ingress Replication. This payload is encapsulated in SR-MPLS or SRv6
and replicated to each egress PE.
3. PMSI Tunnel Attribute for SR P2MP
BGP PMSI Tunnel Attribute (PTA) is defined in RFC 6514 to identify
the P-Tunnel that is used to instantiate a Provider Multicast Service
Interface (PMSI). The PTA is carried in Intra-AS I-PMSI, Inter-AS
I-PMSI, Selective PMSI, and Leaf Auto-Discovery routes.
A P2MP tree PTA is constructed as specified below.
* Tunnel Type: The IANA assigned codepoint 0x0C for "SR-MPLS P2MP
Tree" or codepoint
// TBDfor "SRv6 P2MP Tree", from the "P-Multicast Service
Interface Tunnel (PMSI Tunnel) Tunnel Types" registry.
* Flags: See Section 4 for use of "Leaf Info Required bit".
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* MPLS Label: See Section 3.1
* Tunnel Identifier: The SR P2MP P-Tunnel is identified by <Tree-ID,
Root> where,
- Tree-ID is a 32-bit unsigned value that identifies a unique
P2MP tree at a Root.
- Root is an IP address identifying the Root of a P2MP tree.
This can be either an IPv4 or IPv6 address and can be inferred
from the PTA length.
When a P-Tunnel is non-segmented, the PTA is created by PE router at
the Root of a SR P2MP tree. For segmented P-Tunnels, each segment
can be instantiated by a different technology. If a segment is
instantiated using P2MP tree, the router at the root of a P2MP tree
creates the PTA.
3.1. MPLS Label
[RFC6514] allows a PE to aggregate two or more MVPNs onto one
P-Tunnel by advertising the same P-Tunnel in PTA of Auto-Discovery
routes of different MVPNs. This section specifies how the "MPLS
Label" field of PTA is filled to provide a context bound to a
specific MVPN. For EVPN considerations, see SR P2MP Trees for EVPN
section.
3.1.1. SR-MPLS
When a SR P2MP P-Tunnel is shared across two or more MVPNs in a SR
MPLS domain [RFC8660], the "MPLS Label" field of a PTA advertised in
an Auto-Discovery route MUST contain an upstream-assigned MPLS label
that the advertising PE has bound to the MVPN, or a label assigned
from a global context such as "Domain- wide Common Block" (DCB) as
specified in [I-D.ietf-bess-mvpn-evpn-aggregation-label].
When a customer payload is steered into a shared SR P2MP P-Tunnel,
this MPLS label MUST be imposed before the MPLS label representing
the Tree-SID.
3.1.2. SRv6
When a SR P2MP P-Tunnel is shared across two or more MVPNs in a SRv6
domain [RFC8986], the "MPLS Label" field of a PTA advertised in an
Auto-Discovery route MUST contain an upstream-assigned SRv6 Multicast
Service SID Section 5.2.1 that the advertising PE has bound to the
MVPN, or a SRv6 Multicast Service SID assigned from a global context;
this follows same concept of "Domain- wide Common Block" (DCB) label
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as specified in [I-D.ietf-bess-mvpn-evpn-aggregation-label]. The
high order 20 bits of this field carry the whole or a portion of the
Function part of the SRv6 Multicast Service SID when Transposition
Scheme of encoding as defined in [RFC9252] is used. When using the
Transposition Scheme, the Transposition Length of SRv6 SID Structure
Sub-Sub-TLV of SRv6 Prefix-SID attribute (see below) MUST be less
than or equal to 20 and less than or equal to the Function Length.
When Transposition shceme is not used, the label field MUST be set to
zero and Transposition Length MUST be zero.
The advertising ingress PE attaches a BGP Prefix-SID attribute
[RFC8669] to Intra-AS I-PMSI, Inter-AS I-PMSI or S-PMSI A-D routes
with SRv6 L3 Service TLV [RFC9252] to signal SRv6 Multicast Service
SID. The SRv6 SID Information Sub-TLV carries the SRv6 Multicast
Service SID in SRv6 SID Value field. The SRv6 Endpoint Behavior of
the SRv6 SID Information Sub-TLV encodes one of End.DTMC4, End.DTMC6
or End.DTMC46 codepoint values. The SRv6 SID Structure Sub-Sub-TLV
encodes the structure of SRv6 Multicast Service SID. If
Transposition scheme is used, the offset and length of SRv6 Multicast
Endpoint function of SRv6 Multicast Service SID is set in
Transposition Length and Transposition Offset fields of this sub-sub
TLV. Otherwise, the Transposition Length and Offset fields MUST be
set to zero.
The ingress PE MUST encapsulate customer payload, steered into a
shared SR P2MP P-Tunnel, in an outer IPv6 header with SRH in which
the SRv6 Multicast Service SID MUST be the last segment in the
segment list (note the SRv6 Multicast Service SID may be the only
segment in SRH) . If Transposition scheme is used, ingress PE MUST
merge Function in MPLS Label field of PTA with SRv6 SID in SID
Information TLV using the Transposition Offset and Length fields from
SID structure sub-sub TLV to create SRv6 Multicast Service SID
The Egress PEs of a shared SR P2MP P-Tunnel use the SRv6 Multicast
Service SID in SRH to determine the MVPN in which the customer
payload is to be delivered. An Egress PE, in role of Leaf or Bud
Node of Replication Segment associated with shared SR-P2MP P-Tunnel
tree, uses "look at next SID in SRH"
[I-D.ietf-spring-sr-replication-segment] behavior to process the SRv6
Multicast Service SID.
4. MVPN Auto-Discovery and Binding Procedures for P2MP Trees
RFC 6514 defines procedures for discovering PEs participating in a
given MVPN and binding customer multicast flows to specific
P-Tunnels. This section specifies modifications to these procedures
for SR P2MP tree P-Tunnels. In this section, the term "SR P2MP"
refers to both SR-MPLS and SRv6.
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4.1. Intra-AS I-PMSI
Intra-AS I-PMSI A-D routes are exchanged to discover PEs
participating in a MVPN within an AS, or across different ASes when
non-segmented P-Tunnels are used for inter-AS MVPNs.
4.1.1. Originating Intra-AS I-PMSI routes
RFC 6514 Section 9.1.1 (https://tools.ietf.org/html/rfc6514#section-
9.1.1) describes procedures for originating Intra-AS I-PMSI A-D
routes. For SR P2MP P-Tunnels, these procedures remain unchanged
except as described in the following paragraphs.
When a PE originates an Intra-AS I-PMSI A-D route with a PTA having
SR P2MP P-Tunnel Type, it MUST create a P2MP policy by invoking
CreatePolicy API of the PCE. When the PCE instantiates the P2MP tree
on the PE, the Tree-SID MUST be imposed for customer flow(s) steered
into the P2MP tree. The Leaf nodes of P2MP tree are discovered using
procedures described in Section 4.1.2.
For a PE in "Receiver Sites set", condition (c) is modified to
include P2MP tree; such a PE MUST originate an Intra-AS I-PMSI A-D
route when some PEs of the MVPN have VRFs that use SR P2MP tree but
MUST NOT create a SR P2MP policy as described above.
When a PE withdraws an Intra-AS I-PMSI A-D route, advertised with a
PTA having SR P2MP P-Tunnel Type, the Tree-SID imposition state at
the PE MUST be removed.
A PE MAY aggregate two or more Intra-AS I-PMSIs from different MVPNs
onto the same SR P2MP P-Tunnel. When a PE withdraws the last Intra-
AS I-PMSI A-D route, advertised with a PTA identifying a SR P2MP
P-Tunnel , it SHOULD remove the SR P2MP policy by invoking
DeletePolicy API of the PCE.
4.1.2. Receiving Intra-AS I-PMSI A-D routes
Procedure for receiving Intra-AS I-PMSI A-D routes, as described in
RFC 6514 Section 9.1.2 (https://tools.ietf.org/html/rfc6514#section-
9.1.2), remain unchanged for SR P2MP P-Tunnels except as described in
the following paragraphs.
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When a PE that advertises a SR P2MP P-Tunnel in the PTA of its Intra-
AS I-PMSI A-D route, imports an Intra-AS I-PMSI A-D route from some
PE, it MUST add that PE as a Leaf node of the P2MP tree. The
Originating IP Address of the Intra-AS i-PMSI A-D route is used as
the Leaf Address when invoking UpdateLeafSet API of the PCE. This
procedure MUST also be followed for all Intra-AS I-PMSI routes that
are already imported when the PE advertises a SR P2MP P-Tunnel in PTA
of its Intra-AS I-PMSI A-D route.
A PE that imports and processes an Intra-AS I-PMSI A-D route from
another PE with PTA having SR P2MP P-Tunnel MUST program the Tree-SID
of the P2MP tree identified in the PTA of the route for disposition.
Note that an Intra-AS I-PMSI A-D route from another PE can be
imported before the P2MP tree identified in the PTA of the route is
instantiated by the PCE at the importing PE. In such case, the PE
MUST correctly program Tree-SID for disposition. A PE in "Sender
Sites set" MAY avoid programming the Tree-SID for disposition.
When an Intra-AS I-PMSI A-D route, advertised with a PTA having SR
P2MP P-Tunnel Type is withdrawn, a PE MUST remove the disposition
state of the Tree-SID associated with P2MP tree.
A PE MAY aggregate two or more Intra-AS I-PMSIs from different MVPNs
onto the same SR P2MP P-Tunnel. When a remote PE withdraws an Intra-
AS I-PMSI A-D route from a MVPN, and if this is the last MVPN sharing
a SR P2MP P-Tunnel, a PE must remove the originating PE as a Leaf
from the P2MP tree, by invoking UpdateLeafSet API.
4.2. Using S-PMSIs for binding customer flows to P2MP Segments
RFC 6514 specifies procedures for binding (C-S,C-G) customer flows to
P-Tunnels using S-PMSI A-D routes. Wildcards in Multicast VPN Auto-
Discovery Routes [RFC6625] specifies additional procedures to binding
aggregate customer flows to P-Tunnels using "wildcard" S-PMSI A-D
routes. This section describes modification to these procedures for
SR P2MP P-Tunnels.
4.2.1. Originating S-PMSI A-D routes
RFC 6514 Section 12.1 (https://tools.ietf.org/html/rfc6514#section-
12.1) describes procedures for originating S-PMSI A-D routes. For SR
P2MP P-Tunnels, these procedures remain unchanged except as described
in the following paragraphs.
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When a PE originates S-PMSI A-D route with a PTA having SR P2MP
P-Tunnel Type, it MUST set the "Leaf Info Required bit" in the PTA.
The PE MUST create a SR P2MP policy by invoking CreatePolicy API of
the PCE. When the PCE instantiates the P2MP tree on the PE, the
Tree-SID MUST be imposed for customer flows steered into the SR P2MP
P-Tunnel.
The Leaf nodes of P2MP tree are discovered by Leaf A-D routes using
procedures described in Section 4.4.2. When a PE originates S-PMSI
A-D route with a PTA having SR P2MP P-Tunnel Type, it is possible the
PE might have imported Leaf A-D routes whose route keys match the
S-PMSI A-D route. The PE MUST re-apply procedures of Section 4.4.2
to these Leaf A-D routes.
When a PE withdraws a S-PMSI A-D route, advertised with PTA having
P2MP tree P-Tunnel type, the Tree-SID imposition state MUST be
removed.
A PE MAY aggregate two or more S-PMSIs onto the same SR P2MP
P-Tunnel. When a PE withdraws the last S-PMSI A-D route, advertised
with a PTA identifying a specific SR P2MP P-Tunnel , it SHOULD remove
the SR P2MP policy by invoking DeletePolicy API of the PCE.
4.2.2. Receiving S-PMSI A-D routes
RFC 6514 Section 12.3 (https://tools.ietf.org/html/rfc6514#section-
12.3) describes procedures for receiving S-PMSI A-D routes. For SR
P2MP P-Tunnels, these procedures remain unchanged except as described
in the following paragraphs.
The procedure to join SR P2MP P-Tunnel of S-PMSI A-D route by using a
Leaf A-D route is described in Section 4.4.1. If P2MP tree
identified in PTA of S-PMSI A-D route is already instantiated by PCE,
the PE MUST program Tree-SID for disposition. If the P2MP tree is
instantiated later, the Tree-SID MUST be programmed for disposition
at that time.
When a S-PMSI A-D route, whose SR P2MP P-Tunnel has been joined by a
PE, is withdrawn, or when conditions (see RFC 6514 Section 12.3
(https://tools.ietf.org/html/rfc6514#section-12.3)) required to join
that P-Tunnel are no longer satisfied, the PE MUST leave the
P-Tunnel. The PE MUST withdraw the Leaf A-D route it had originated
and remove the Tree-SID disposition state.
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4.3. Inter-AS P-tunnels using P2MP Segments
A segmented inter-AS P-Tunnel consists of one or more intra-AS
segments, one in each AS, connected by inter-AS segments between
ASBRs of different ASes https://tools.ietf.org/html/rfc6514#section-
9.2. These segments are constructed by PEs/ASBRs originating or re-
advertising Inter-AS I-PMSI A-D routes. This section describes
procedures for instantiating intra-AS segments using SR P2MP trees.
4.3.1. Advertising Inter-AS I-PMSI routes into iBGP
RFC 6514 Section 9.2.3.2 (https://tools.ietf.org/html/
rfc6514#section-9.2.3.2) specifies procedures for advertising an
Inter-AS I-PMSI A-D route to construct an intra-AS segment. The PTA
of the route identifies the type and identifier of the P-Tunnel
instantiating the intra-AS segment. The procedure for creating SR
P2MP P-Tunnel for intra-AS segment are same as specified in
Section 4.2.1 except that instead of S-PMSI A-D routes, the
procedures apply to Inter-AS I-PMSI A-D routes.
4.3.2. Receiving Inter-AS I-PMSI A-D routes in iBGP
RFC 6514 Section 9.2.3.2 (https://tools.ietf.org/html/
rfc6514#section-9.2.3.2) specifies procedures for processing an
Inter-AS I-PMSI A-D route received via iBGP. If the PTA of the
Inter-AS I-PMSI A-D route has SR P2MP P-Tunnel Type, the procedures
are same as specified in Section 4.2.2 except that instead of S-PMSI
A-D routes, the procedures apply to Inter-AS I-PMSI A-D routes. If
the receiving router is an ASBR, the Tree-SID is stitched to the
inter-AS segments to ASBRs in other ASes.
4.4. Leaf A-D routes for P2MP Segment Leaf Discovery
This section describes procedures for originating and processing Leaf
A-D routes used for Leaf discovery of SR P2MP trees.
4.4.1. Originating Leaf A-D routes
The procedures for originating Leaf A-D route in response to
receiving a S-PMSI or Inter-AS I-PMSI A-D route with PTA having SR
P2MP P-Tunnel Type are same as specified in RFC 6514
Section 9.2.3.4.1 (https://tools.ietf.org/html/rfc6514#section-
9.2.3.4.1).
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4.4.2. Receiving Leaf A-D routes
Procedures for processing a received Leaf A-D route are specified in
RFC 6514 Section 9.2.3.5 (https://tools.ietf.org/html/
rfc6514#section-9.2.3.5). These procedures remain unchanged for
discovering Leaf nodes of P2MP trees except for considerations
described in following paragraphs. These procedures apply to Leaf
A-D routes received in response to both S-PMSI and Inter-AS I-PMSI
A-D routes, shortened to "A-D routes" in this section
A Root PE/ASBR MAY use the same SR P2MP P-Tunnel in PTA of two or
more A-D routes. For such aggregated P2MP trees, the PE/ASBR may
receive multiple Leaf A-D routes from a Leaf PE. The P2MP tree for
which a Leaf A-D is received can be identified by examining the P2MP
tunnel Identifier in the PTA of A-D route that matches "Route Key"
field of the Leaf A-D route. When the PE receives the first Leaf A-D
route from a Leaf PE, identified by the Originating Router's IP
address field, it MUST add that PE as Leaf of the P2MP tree by
invoking the UpdateLeafSet API of the PCE.
When a Leaf PE withdraws the last Leaf A-D route for a given SR P2MP
P-Tunnel, the Root PE MUST remove the Leaf PE from the P2MP tree by
invoking UpdateLeafSet API of PCE. Note that Root PE MAY remove the
P2MP tree, via the DeletePolicyAPI, before the last Leaf A-D is
withdrawn. In this case, the Root PE MAY decide to not invoke the
UpdateLeafSet API.
5. MVPN with Ingress Replication over Segment Routing
A PE can provide MVPN service using Ingress Replication over Segment
Routing. Customer payload is encapsulated in SR-MPLS or IPv6 (SRv6)
at Ingress PE. The encapsulated payload is replicated and a unicast
copy is sent to each egress PE.
Ingress Replication Tunnels in Multicast VPN [RFC7988] specifies
procedures that can be used to provide MVPN service with Ingress
Replication in a Segment Routing domain. A PE advertises Intra-AS,
Inter-AS, Selective PMSI BGP Auto-Discovery routes with PTA for
Ingress Replication. Egress PEs join asLeaf Nodes using Intrra-AS
I-PMSI or Leaf Auto-Discovery routes.
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RFC 7988 procedures allow an ingress PE to deliver MVPN traffic to
egress PEs using best-effort unicast connectivity. For MVPN service
with an underlay SLA from ingress PE to an egress PE, the egress PE
colors the Leaf Auto-Discovery route with a Color Extended Community
as specified in [I-D.ietf-idr-segment-routing-te-policy]. The
ingress PE replicates MVPN customer payload to that egress PE by
steering traffic into a SR-TE policy (Color, egress PE) according to
section 8 of [RFC9256].
5.1. SR-MPLS
Procedures of RFC 7988 are sufficient to create a SR-MPLS Ingress
Replication for MVPN service.
If an egress PE colors the Leaf A-D route with Color Extended
Community, the ingress PE encapsulates the payload packet into
segment list of (Color, egress PE) SR-TE policy along with IR label
received from the egress PE. Suppose the egress PE, say PE2, sends
Leaf A-D route with extended color community C1 and IR label L10.
Assume the segment list of SR-TE policy (C1, PE2) at ingress PE1 is
<L1, L2, L3>, PE1 will encapsulate MVPN customer payload into MPLS
label stack <L1, L2, L3, L10> with L10 as BoS label.
5.2. SRv6
Procedures of RFC 7988, along with modifications described in this
Section, are sufficient to create a SRv6 Ingress Replication for MVPN
service.
The PTA carried in Intra-AS, Inter-AS, Selective PMSI and Leaf Auto-
Discovery routes is constructed as specified in RFC 7988 with
modifications as below:
* Tunnel Type: "Ingress Replication" as per RFC 6514.
* MPLS Label: The high order 20 bits of this field carry the whole
or a portion of the Function part of the SRv6 Multicast Service
SID when ingress replication is used with the Transposition Scheme
of encoding as defined in [RFC9252]. When using the Transposition
Scheme, the Transposition Length of SRv6 SID Structure Sub-Sub-TLV
of SRv6 Prefix-SID attribute (see below) MUST be less than or
equal to 20 and less than or equal to the Function Length. When
Transposition shceme is not used, the label field MUST be set to
zero and Transposition Length MUST be zero.
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Section 6 and 7 of RFC 7988 (https://datatracker.ietf.org/doc/html/
rfc7988#section-6) describe considerations and procedures for
allocating MPLS labels for IR P-Tunnel. For SRv6 Ingress
Replication, these sections apply to SRv6 Multicast Service SID.
To join a SRv6 Ingres Replication P-Tunnel advertised in PTA of Inra-
AS, Inter-AS, or Selective S-PMSI A-D routes, an egress PE constructs
a Leaf A-D or Intra-AS I-PMSI route as described in RFC 7988 with
modified PTA above. The egress PE attaches a BGP Prefix-SID
attribute [RFC8669] in Leaf A-D or Intra-AS I-PMSI route with SRv6 L3
Service TLV [RFC9252] to signal SRv6 Multicast Service SID . The SRv6
SID Information Sub-TLV carries the SRv6 Multicast Service SID in
SRv6 SID Value field. The SRv6 Endpoint Behavior of the SRv6 SID
Information Sub-TLV encodes one of End.DTMC4, End.DTMC6 or End.DTMC46
codepoint value. The SRv6 SID Structure Sub-Sub-TLV encodes the
structure of SRv6 Multicast Service SID. If Transposition scheme is
used, the offset and length of SRv6 Multicast Endpoint function of
SRv6 Multicast Service SID is set in Transposition Length and
Transposition Offset fields of this sub-sub TLV. Otherwise, the
Transposition Length and Offset fields MUST be set to zero. The BGP
Prefix SID attribute with SRv6 L3 Service TLV in Intra-AS I-PMSI or
Leaf A-D route indicates to ingress PE that egress PE supports SRv6.
The SRv6 Multicast Service SID SHOULD be routable within the AS of
the egress PE. As per RFC 7988, the Ingress PE uses the Tunnel
Identifier of PTA to determine the unicast tunnel to use in order to
send data to the egress PE. This document requires the ingress PE to
use the SRv6 Multicast Service SID to determine the unicast tunnel to
be used. For best-effort MVPN service or SLA based MVPN service
using IGP Flexible Algorithm, the ingress PE MUST encapsulate payload
in an outer IPv6 header with the SRv6 Multicast Service SID provided
by the egress PE as the destination address. If Transposition scheme
is used, ingress PE MUST merge Function in MPLS Label field of PTA
with SRv6 SID in SID Information TLV using the Transposition Offset
and Length fields from SID structure sub-sub TLV to create SRv6
Multicast Service SID
If an egress PE colors a Leaf A-D route with Color Extended
Community, the ingress PE SHOULD encapsulate the payload packet into
outer IPv6 header with segment list of (Color, egress PE) SR-TE
policy along with SRv6 Multicast Service SID received with Leaf A-D
route from the egress PE using SRH. Suppose the egress PE, say PE2,
sends Leaf A-D route with extended color community C1 and SRv6
Multicast Service SID S10. Assume the segment list of SR-TE policy
(C1, PE2) at ingress PE1 is <S1, S2, S3>, PE1 will encapsulate MVPN
customer payload into IPv6 header with SRH (PE1, S1) (S10, S3, S2;
SL=3) (payload). If SRv6 SID compression is used, the ingress PE
SHOULD use CSID containers for the policy segments.
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5.2.1. SRv6 Multicast Endpoint Behaviors
The following behaviors can be associated with SRv6 Multicast Service
SID.
5.2.1.1. End.DTMC4: Decapsulation and Specific IPv4 Multicast
Table Lookup
The "Endpoint with decapsulation and specific IPv4 Multicast table
lookup" behavior ("End.DTMC4" for short) is similar to End.DT4
behavior of RFC 8986 except the lookup is in IPv4 multicast table.
5.2.1.2. End.DTMC6: Decapsulation and Specific IPv6 Multicast
Table Lookup
The "Endpoint with decapsulation and specific IPv6 Multicast table
lookup" behavior ("End.DTMC6" for short) is similar to End.DT6
behavior of RFC 8986 except the lookup is in IPv6 multicast table.
5.2.1.3. End.DTMC46: Decapsulation and Specific IP Multicast
Table Lookup
The "Endpoint with decapsulation and specific IP Multicast table
lookup" behavior ("End.DTMC46" for short) is similar to End.DT4 and
End.DT6 behaviors of RFC 8986 except the lookup is in IP multicast
table.
6. Dampening of MVPN routes
When P2MP trees are used as P-Tunnels for S-PMSI A-D routes, change
in group membership of receivers connected to PEs has direct impact
on the Leaf node set of a P2MP tree. If group membership changes
frequently for a large number of groups with a lot of receivers
across sites connected to different PEs, it can have an impact on the
interaction between PEs and the PCE.
Since Leaf A-D routes are used to discover Leaf PE of a P2MP tree, it
is RECOMMENDED that PEs SHOULD damp Leaf A-D routes as described in
Section 6.1 of RFC 7899 [RFC7899]. PEs MAY also implement procedures
for damping other Auto-Discovery and BGP C-multicast routes as
described in [RFC7899].
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7. SR P2MP Trees for EVPN
BGP MPLS Ethernet VPN specified in RFC 7432 specifies Inclusive
Multicast Ethernet Tag route to support Broadcast, Unknown Unicast
and Multicast (BUM) traffic. This IMET route is the equivalent of
MVPN Intra-AS I-PMSI route and is advertised with a PMSI Tunnel
Attribute (PTA) as specified in RFC 6514 to advertise the inclusive
P-Tunnels.
[I-D.ietf-bess-evpn-bum-procedure-updates] updates BUM procedures to
support selective P-Tunnels and P-Tunnel segmentation in EVPN. That
document specifies new route types that are advertised with PTA,
including Selective PMSI (S-PMSI) Auto-Discovery route.
These inclusive/selective P-Tunnels can be realized by SR P2MP trees.
As with other types of P2MP P-Tunnels, the ESI label used for split
horizon MUST be either upstream assigned by PE advertising the IMET
or S-PMSI route, or assigned from a global context such as "Domain-
wide Common Block" (DCB) as specified in
[I-D.ietf-bess-mvpn-evpn-aggregation-label].
[I-D.ietf-bess-evpn-irb-mcast] specifies procedures to support Inter-
Subnet Multicast. [I-D.ietf-bess-evpn-mvpn-seamless-interop]
specifies how MVPN SAFI routes can be used to support Inter-Subnet
Multicast. The P-Tunnels advertised in PTA of either EVPN and MVPN
routes as specified in these documents respectively can be realized
by SR P2MP trees.
SRv6 P2MP trees can serve as an underlay multicast as described in
RFC 8293 Section 3.4 (https://tools.ietf.org/html/rfc8293#section-
3.4). A NVE encapsulates a tenant packet in an SRv6 header and
deliver it over SRv6 P2MP trees to other NVEs.
The same procedures specified for MVPN are used to collect the leaf
information of corresponding SR P2MP tree (either based on IMET route
or Leaf A-D routes in response to x-PMSI routes), to pass the tree
information to the PCE controller, and to get back tree forwarding
state used for customer multicast traffic forwarding.
8. IANA Considerations
IANA has assigned the value 0x0C for "SR-MPLS P2MP Tree" in the
"P-Multicast Service Interface Tunnel (PMSI Tunnel) Tunnel Types"
registry https://www.iana.org/assignments/bgp-parameters/bgp-
parameters.xhtml#pmsi-tunnel-types [RFC 7385] in the "Border Gateway
Protocol (BGP) Parameters" registry.
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IANA is requested to assign codepoint for "SRv6 P2MP Tree" in the
"P-Multicast Service Interface Tunnel (PMSI Tunnel) Tunnel Types"
registry https://www.iana.org/assignments/bgp-parameters/bgp-
parameters.xhtml#pmsi-tunnel-types [RFC 7385] in the "Border Gateway
Protocol (BGP) Parameters" registry. A proposed value is 0x0D.
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 |
+=======+========+===================+===========+
| 76 | 0x004C | End.DTMC4 | [This.ID] |
+-------+--------+-------------------+-----------+
| 77 | 0x004D | End.DTMC6 | [This.ID] |
+-------+--------+-------------------+-----------+
| 78 | 0x004E | End.DTMC46 | [This.ID] |
+-------+--------+-------------------+-----------+
Table 1: IETF - SRv6 Endpoint Behaviors
9. Security Considerations
The procedures in this document do not introduce any additional
security considerations beyond those mentioned in [RFC6513] and
[RFC6514]. For general security considerations applicable to P2MP
trees, please refer to [I-D.ietf-pim-sr-p2mp-policy] .
10. Acknowledgements
The authors would like to acknowledge Luc Andre Burdett reviewing the
document..
11. Contributors
Zafar Ali Cisco Systems, Inc. US
Email: zali@cisco.com
Ehsan Hemmati Cisco Systems, Inc. US
Email: ehemmati@cisco.com
Jayant Kotalwar Nokia Mountain View US
Email: jayant.kotalwar@nokia.com
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Tanmoy Kundu Nokia Mountain View US
Email: tanmoy.kundu@nokia.com
Clayton Hassen Bell CanadaVancouver CA
Email: clayton.hassen@bell.ca
12. References
12.1. Normative References
[I-D.ietf-pim-sr-p2mp-policy]
Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z.
J. Zhang, "Segment Routing Point-to-Multipoint Policy",
Work in Progress, Internet-Draft, draft-ietf-pim-sr-p2mp-
policy-07, 11 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-pim-sr-
p2mp-policy-07>.
[I-D.ietf-spring-sr-replication-segment]
Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z.
J. Zhang, "SR Replication segment for Multi-point Service
Delivery", Work in Progress, Internet-Draft, draft-ietf-
spring-sr-replication-segment-19, 28 August 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
sr-replication-segment-19>.
[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>.
[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>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[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>.
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[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[RFC8669] Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah,
A., and H. Gredler, "Segment Routing Prefix Segment
Identifier Extensions for BGP", RFC 8669,
DOI 10.17487/RFC8669, December 2019,
<https://www.rfc-editor.org/info/rfc8669>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[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>.
[RFC9252] Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene,
B., Zhuang, S., and J. Rabadan, "BGP Overlay Services
Based on Segment Routing over IPv6 (SRv6)", RFC 9252,
DOI 10.17487/RFC9252, July 2022,
<https://www.rfc-editor.org/info/rfc9252>.
12.2. Informative References
[I-D.ietf-bess-evpn-bum-procedure-updates]
Zhang, Z. J., Lin, W., Rabadan, J., Patel, K., and A.
Sajassi, "Updates on EVPN BUM Procedures", Work in
Progress, Internet-Draft, draft-ietf-bess-evpn-bum-
procedure-updates-14, 18 November 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-bum-procedure-updates-14>.
[I-D.ietf-bess-evpn-irb-mcast]
Lin, W., Zhang, Z. J., Drake, J., Rosen, E. C., Rabadan,
J., and A. Sajassi, "EVPN Optimized Inter-Subnet Multicast
(OISM) Forwarding", Work in Progress, Internet-Draft,
draft-ietf-bess-evpn-irb-mcast-09, 21 February 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-irb-mcast-09>.
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[I-D.ietf-bess-evpn-mvpn-seamless-interop]
Sajassi, A., Thiruvenkatasamy, K., Thoria, S., Gupta, A.,
and L. Jalil, "Seamless Multicast Interoperability between
EVPN and MVPN PEs", Work in Progress, Internet-Draft,
draft-ietf-bess-evpn-mvpn-seamless-interop-06, 23 October
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
bess-evpn-mvpn-seamless-interop-06>.
[I-D.ietf-bess-mvpn-evpn-aggregation-label]
Zhang, Z. J., Rosen, E. C., Lin, W., Li, Z., and I.
Wijnands, "MVPN/EVPN Tunnel Aggregation with Common
Labels", Work in Progress, Internet-Draft, draft-ietf-
bess-mvpn-evpn-aggregation-label-14, 4 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
mvpn-evpn-aggregation-label-14>.
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and
D. Jain, "Advertising Segment Routing Policies in BGP",
Work in Progress, Internet-Draft, draft-ietf-idr-segment-
routing-te-policy-26, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-26>.
[RFC6625] Rosen, E., Ed., Rekhter, Y., Ed., Hendrickx, W., and R.
Qiu, "Wildcards in Multicast VPN Auto-Discovery Routes",
RFC 6625, DOI 10.17487/RFC6625, May 2012,
<https://www.rfc-editor.org/info/rfc6625>.
[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>.
[RFC7899] Morin, T., Ed., Litkowski, S., Patel, K., Zhang, Z.,
Kebler, R., and J. Haas, "Multicast VPN State Damping",
RFC 7899, DOI 10.17487/RFC7899, June 2016,
<https://www.rfc-editor.org/info/rfc7899>.
[RFC8293] Ghanwani, A., Dunbar, L., McBride, M., Bannai, V., and R.
Krishnan, "A Framework for Multicast in Network
Virtualization over Layer 3", RFC 8293,
DOI 10.17487/RFC8293, January 2018,
<https://www.rfc-editor.org/info/rfc8293>.
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[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
Authors' Addresses
Rishabh Parekh
Cisco Systems, Inc.
170 W. Tasman Drive
San Jose, CA 95134
United States of America
Email: riparekh@cisco.com
Clarence Filsfils
Cisco Systems, Inc.
Brussels
Belgium
Email: cfilsfil@cisco.com
Arvind Venkateswaran
Cisco Systems, Inc.
170 W. Tasman Drive
San Jose, CA 95134
United States of America
Email: arvvenka@cisco.com
Hooman Bidgoli
Nokia
Ottawa
Canada
Email: hooman.bidgoli@nokia.com
Daniel Voyer
Bell Canada
Montreal
Canada
Email: daniel.voyer@bell.ca
Zhaohui Zhang
Juniper Networks
Email: zzhang@juniper.net
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