Internet DRAFT - draft-ietf-bess-bgp-multicast
draft-ietf-bess-bgp-multicast
BESS Z. Zhang
Internet-Draft L. Giuliano
Intended status: Standards Track Juniper Networks
Expires: 4 June 2024 K. Patel
I. Wijnands
Arrcus
M. Mishra
Cisco Systems
A. Gulko
EdwardJones
2 December 2023
BGP Based Multicast
draft-ietf-bess-bgp-multicast-07
Abstract
This document specifies a BGP address family and related procedures
that allow BGP to be used for setting up multicast distribution
trees. This document also specifies procedures that enable BGP to be
used for multicast source discovery, and for showing interest in
receiving particular multicast flows. Taken together, these
procedures allow BGP to be used as a replacement for other multicast
routing protocols, such as PIM or mLDP. The BGP procedures specified
here are based on the BGP multicast procedures that were originally
designed for use by providers of Multicast Virtual Private Network
service.
This document also describes how various signaling mechanisms can be
used to set up end-to-end inter-region multicast trees.
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 4 June 2024.
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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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Motivation . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.1. Native/unlabeled Multicast . . . . . . . . . . . . . 5
1.2.2. Labeled Multicast . . . . . . . . . . . . . . . . . . 6
1.3. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.1. (x,G) Multicast . . . . . . . . . . . . . . . . . . . 7
1.3.1.1. Source Discovery for ASM . . . . . . . . . . . . 8
1.3.1.2. ASM Shared-tree-only Mode . . . . . . . . . . . . 8
1.3.1.3. Integration with BGP-MVPN . . . . . . . . . . . . 9
1.3.2. BGP Inband Signaling for mLDP Tunnels . . . . . . . . 9
1.3.3. BGP Sessions . . . . . . . . . . . . . . . . . . . . 9
1.3.4. LAN and Parallel Links . . . . . . . . . . . . . . . 10
1.3.5. Transition . . . . . . . . . . . . . . . . . . . . . 11
1.3.6. Inter-region Multicast . . . . . . . . . . . . . . . 12
1.3.6.1. Inband Signaling across a Region . . . . . . . . 12
1.3.6.2. Overlay Signaling Over a Region . . . . . . . . . 13
1.3.6.3. Controller Based Signaling . . . . . . . . . . . 14
1.3.7. BGP Classful Transport Planes . . . . . . . . . . . . 14
1.3.8. Flexible Algorithm and Multi-topology . . . . . . . . 15
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2. Specification . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1. BGP NLRIs and Attributes . . . . . . . . . . . . . . . . 15
2.1.1. S-PMSI A-D Route . . . . . . . . . . . . . . . . . . 16
2.1.2. Leaf A-D Route . . . . . . . . . . . . . . . . . . . 17
2.1.3. Source Active A-D Route . . . . . . . . . . . . . . . 18
2.1.4. S-PMSI A-D Route for mLDP . . . . . . . . . . . . . . 19
2.1.5. Session Address Extended Community . . . . . . . . . 19
2.1.6. Multicast RPF Address Extended Community . . . . . . 20
2.1.7. Topology/IPA Extended Community . . . . . . . . . . . 20
2.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.1. Source Discovery for ASM . . . . . . . . . . . . . . 20
2.2.2. Originating Tree Join Routes . . . . . . . . . . . . 21
2.2.2.1. (x,G) Multicast Tree . . . . . . . . . . . . . . 21
2.2.2.2. BGP Inband Signaling for mLDP Tunnel . . . . . . 22
2.2.3. Receiving Tree Join Routes . . . . . . . . . . . . . 22
2.2.4. Withdrawal of Tree Join Routes . . . . . . . . . . . 23
2.2.5. LAN procedures for (x,G) Unidirectional Tree . . . . 23
2.2.5.1. Originating S-PMSI A-D Routes . . . . . . . . . . 23
2.2.5.2. Receiving S-PMSI A-D Routes . . . . . . . . . . . 23
2.2.6. Distributing Label for Upstream Traffic for
Bidirectional Tree/Tunnel . . . . . . . . . . . . . . 24
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
4. Security Considerations . . . . . . . . . . . . . . . . . . . 25
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.1. Normative References . . . . . . . . . . . . . . . . . . 26
6.2. Informative References . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
1.1. Terminology
This document assumes the readers are familiar with basic multicast
concepts. Some terminologies are included here for convenience.
PIM: Protocol Independent Multicast [RFC7761].
ASM: All/Any Source Multicast. A multicast mode where a receiver
is interested in receiving traffic for a multicast group from
anywhere.
SSM: Source-Specific Multicast [RFC7761].
PIM-ASM: PIM procedures for ASM.
PIM-SSM: PIM procedures for SSM.
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PIM-Port: PIM Over Reliable Transportation [RFC6559].
PIM-Bidir: PIM procedures for bidirectional shared trees
connecting multicast sources and receivers [RFC5015].
RP: Rendezvous Point, the root of the non-source-specific
distribution tree for a multicast group [RFC7761].
RPA: Rendezvous Point Address for the root of a bidirectional
distribution tree for a range of multicast groups [RFC5015].
RPL: Rendezvous Point Link, the link to which the RPA belongs.
RPF: Reverse Path Forwarding, by which multicast traffic is
forwarded from the root of a multicast tree in the reverse path on
which the tree leaves would reach the root.
FHR: First Hop Router (connecting to a multicast source)
[RFC7761].
LHR: Last Hop Router (connecting to a multicast receiver)
[RFC7761].
(x,G): An IP multicast flow/tree for a group G, where x is either
an 'S' for a specific source or a '*' for all sources.
IGMP: Internet Group Management Protocol [RFC3376].
MLD: Multicast Listener Discovery [RFC3810].
P2MP: Point-to-MultiPoint.
MP2MP: MultiPoint-to-MultiPoint.
mLDP: Label Distribution Protocol Extensions for P2MP and MP2MP
Label Switched Paths [RFC6388].
S-PMSI: Selective Provider Multicast Service Interface. In
[RFC6514], the term refers to a pseudo-interface used to send
customer multicast to a subset of Provider Edge routers, and
S-PMSI Auto-Discovery (A-D) routes are used to advertise the
binding of customer multicast flows to a tunnel that instantiates
a pseudo-interface. In this document, S-PMSI A-D routes are used
for various purposes as described in Section 2.2.5 and
Section 2.2.6.
PTA: PMSI Tunnel Attribute [RFC6514]. An attribute carried in an
S-PMSI A-D route that specifies the tunnel instantiating the PMSI.
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EC: BGP Extended Community.
RT: BGP Route Target.
RTC: Route Target Constrain (RTC) [RFC4684].
1.2. Motivation
This section provides some motivation for BGP signaling for native
and labeled multicast. One target deployment would be a Data Center
(DC) that requires multicast but uses BGP as its only routing
protocol [RFC7938]. In such a deployment, it would be desirable to
support multicast by extending the deployed routing protocol, without
requiring the deployment of tree-building protocols such as PIM,
mLDP, and without requiring an IGP.
Additionally, compared to PIM, BGP-based signaling has several
advantage as described in the following section, and may be desired
in non-DC deployment scenarios as well.
1.2.1. Native/unlabeled Multicast
Protocol Independent Multicast (PIM) [RFC7761] has been the
prevailing multicast protocol for many years. Despite its success,
it has two drawbacks:
* The ASM model, which is prevalent, introduces complexity in the
following areas: source discovery procedures, need for Rendezvous
Points (RPs) and group-to-RP mappings, need to switch between RP-
rooted trees and source-rooted trees, etc.
* Periodical protocol state refreshes due to soft state nature.
PIM-SSM removes much of the complexity of PIM-ASM by moving source
discovery to the application layer. However, for various reasons,
many legacy applications and devices still rely upon network-based
source discovery. PIM Over Reliable Transport (PORT) [RFC6559]
solves the soft state issue, though its deployment has also been
limited for two reasons:
* It does not remove the ASM complexities.
* In many of the scenarios where reliable transport is deemed
important, BGP-based multicast (e.g. BGP-MVPN) has been used
instead of PORT.
Partly because of the above-mentioned problems, some Data Center
operators have been avoiding deploying multicast in their networks.
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BGP-MVPN [RFC6514] uses BGP to signal VPN customer multicast state
over provider networks. It removes the above-mentioned problems from
the Service Provider (SP) environment and has been widely deployed.
While RFC 6514 enables an SP to provide MVPN service without running
PIM on its backbone, it assumes that PIM (or mLDP) runs on the PE-CE
links. [I-D.ietf-bess-mvpn-pe-ce] adapts the concept of BGP-MVPN to
PE-CE links so that the use of PIM on the PE-CE links can be
eliminated (though the PIM-ASM complexities still remain in the
customer network), and this document extends it further to general
topologies, so that they can be run on any router, as a replacement
for PIM or mLDP.
With that, PIM can be eliminated from the network. PIM soft state is
replaced by BGP hard state. For ASM, source-specific trees are set
up directly after simpler source discovery (data-driven on FHRs and
control-driven elsewhere), all based on BGP. All the complexities
related to source discovery and shared/source tree switch are also
eliminated. Additionally, the trees can be set up with MPLS labels,
with just minor enhancements in the signaling.
1.2.2. Labeled Multicast
There could be two forms of labeled multicast signaled by BGP. The
first one is labeled (x,G) multicast where 'x' stands for either 'S'
or '*'. Basically, it is for a BGP-signaled multicast tree as
described in the previous section but with labels. The second one is
for mLDP tunnels with BGP signaling in part or whole through a BGP
domain.
For both cases, BGP is used because other label distribution
mechanisms like mLDP may not be desired by some operators. For
example, a DC operator may prefer to have a BGP-only deployment.
1.3. Overview
This overview section describes the mode of operation and some
considerations.
At a very high level, PIM Join messages or mLDP Label mapping
messages are replaced by BGP updates of MCAST-TREE SAFI with the
following NLRI format (Section 2.1):
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+-----------------------------------+
| Route Type (1 octet) |
+-----------------------------------+
| Length (1 octet) |
+-----------------------------------+
| Route Type specific (variable) |
+-----------------------------------+
Different route types are described in this section as they are
encountered.
1.3.1. (x,G) Multicast
PIM/mLDP-like functionality is provided, using BGP-based join
signaling and BGP-based source discovery in the case of ASM. The
BGP-based join signaling supports both labeled multicast and IP
multicast.
The same RPF procedures as in PIM/mLDP are used for each router to
determine the RPF neighbor for a particular source or RPA (in the
case of Bidirectional Tree) or root. Except in the Bidirectional
Tree case and a special case described in Section 1.3.1.2, no (*,G)
join is used - LHR routers discover the sources for ASM and then join
towards the sources directly. Data-driven mechanisms like PIM Assert
are replaced by control-driven mechanisms (Section 1.3.4).
One of the route types is Leaf A-D route - the equivalent of a PIM
Join message or mLDP Label Mapping message. The Leaf A-D routes are
targeted at the upstream neighbor by use of Route Targets. In some
cases, S-PMSI A-D routes are also used, as described in some sections
below.
If the BGP updates carry labels (via Tunnel Encapsulation Attribute
[RFC9012]), then (S,G) multicast traffic can use the labels. This is
very similar to mLDP Inband Signaling [RFC6826], except that there
are no corresponding "mLDP tunnels" for the PIM trees. Similar to
mLDP, labeled traffic on transit Local Area Networks (LANs) are point
to point. Of course, traffic sent to receivers on a LAN by a LHR is
native multicast.
For labeled bidirectional (*,G) trees, downstream traffic (away from
the RPA) is forwarded as in the (S,G) case. For upstream traffic
(towards RPA), the upstream neighbor needs to advertise a label for
its downstream neighbors. The same label that the upstream neighbor
advertises to its upstream in a Leaf A-D route is the same one that
it advertises to its downstreams using an S-PMSI A-D route.
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1.3.1.1. Source Discovery for ASM
This document does not support ASM via shared trees (aka RP Tree, or
RPT) with one exception discussed in the next section. Instead,
FHRs, LHRs, and optionally RRs work together to propagate/discover
source information via control plane and LHRs join source-specific
Shortest Path Trees (SPT) directly.
An FHR originates Source Active (SA) A-D routes upon discovering
sources for particular flows and advertises them to its peers. Route
targets are used so that the SA routes only reach LHRs that are
interested in receiving the traffic (Section 2.2.1).
Typically, a set of RRs are used and they maintain all Source Active
routes but only distribute to interested LHRs on demand. The rest of
the document assumes that RRs are used, even though that is not
required.
That the set of RRs maintain all SA routes is comparable to that the
RPs in PIM-ASM maintain all (S,G) states in the network. In fact, in
PIM-ASM case the states are maintained in both the control plane and
data plane, while in the case of BGP SA-based discovery, the states
are only maintained in the control plane, and the RRs can be placed
outside the traffic path.
Note that the data-driven source discovery and subsequent control-
driven tree setup means receivers will miss the initial packets of a
multicast flow when it just starts or resumes. If it is important to
avoid this, source discovery should be provided by the application
layer instead of the network.
1.3.1.2. ASM Shared-tree-only Mode
It may be desired that only a shared tree is used to distribute all
traffic for a particular ASM group from its RP to all LHRs, as
described in Section 4.1 "PIM Shared Tree Forwarding" of [RFC7438].
This will significantly cut down the number of trees and works out
very well in certain deployment scenarios. For example, all the
sources could be connected to the RP, or clustered close to the RP.
In the latter case, either the paths from FHRs to the RP do not
intersect the shared tree so native forwarding can be used between
the FHRs and the RP, or other means outside of this document could be
used to forward traffic from FHRs to the RP.
For native forwarding from FHRs to the RP, SA routes may be used to
announce the sources so that the RP can join source-specific trees to
pull traffic, but the LHRs do not advertise the group-specific Route
Target Membership routes as they do not need the SA routes.
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To establish the shared tree, (*,G) Leaf A-D routes are originated
hop-by-hop towards the RP, and corresponding (*,G) forwarding states
are established along the way, just like how (S,G) Leaf A-D routes
are originated hop-by-hop towards the source and (S,G) forwarding
sates are established along the way.
1.3.1.3. Integration with BGP-MVPN
For each VPN, the Source Active routes distribution in that VPN do
not have to involve PEs at all (unless there are sources/receivers
directly connected to some PEs) and they are independent of MVPN SA
routes. For example, FHRs and LHRs establish BGP sessions with RRs
of that particular VPN for the purpose of SA distribution.
After source discovery, BGP multicast signaling is done from LHRs
towards the sources. When the signaling reaches an egress PE, BGP-
MVPN signaling takes over, as if a PIM (S,G) join was received on the
PE-CE interface. When the BGP-MVPN signaling reaches the ingress PE,
BGP multicast signaling as specified in this document takes over,
similar to how BGP-MVPN triggers PIM (S,G) join on PE-CE interfaces.
1.3.2. BGP Inband Signaling for mLDP Tunnels
Part of an (or the whole) mLDP tunnel can also be signaled via BGP
and seamlessly integrated with the rest of mLDP tunnel signaled
natively via mLDP. All the procedures are similar to mLDP except
that the signaling is done via BGP. The mLDP FEC is encoded in the
BGP NLRI, with MCAST-TREE SAFI and S-PMSI/Leaf A-D Routes for mLDP
defined in this document. The Leaf A-D routes correspond to mLDP
Label Mapping messages and the S-PMSI A-D routes are used to signal
upstream FEC for MP2MP mLDP tunnels, similar to the bidirectional
(*,G) case.
1.3.3. BGP Sessions
In order for two BGP speakers to exchange MCAST-TREE NLRI, they MUST
use BGP Capabilities Advertisement [RFC5492] to ensure that they both
are capable of properly processing the MCAST-TREE NLRI. This is done
as specified in [RFC4760], by using a capability code 1
(multiprotocol BGP) with an AFI of IPv4 (1) or IPv6 (2) and a SAFI of
MCAST-TREE (78).
How the BGP peer sessions are provisioned, whether EBGP or IBGP,
whether statically, automatically, or programmably via an external
controller, is outside the scope of this document.
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In the case of IBGP, it could be that every router peering with Route
Reflectors, or hop-by-hop IBGP sessions could be used to exchange
MCAST-TREE NLRIs for joins. In the latter case, unless desired
otherwise for reasons outside of the scope of this document, the hop-
by-hop IBGP sessions SHOULD only be used to exchange MCAST-TREE
NLRIs.
When multihop BGP is used, a router advertises its local interface
addresses, for the same purposes that the Address List TLV in LDP
serves. This is achieved by advertising the interface address as
host prefixes with IPv4/v6 Address Specific Extended Community (EC)
corresponding to the router's local address used for its BGP sessions
(Section 2.1.5).
Because the BGP Capability Advertisement is only between two peers,
when the sessions are only via RRs, a router needs another way to
determine if its neighbor is capable of signaling multicast via BGP.
The interface address advertisement can be used for that purpose -
the inclusion of a Session Address EC indicates that the BGP speaker
identified in the EC supports the MCAST-TREE NLRIs.
FHRs and LHRs may also establish BGP sessions to some Route
Reflectors for source discovery purposes (Section 1.3.1.1).
With the traditional PIM, the FHRs and LHRs refer to the PIM
Desginated Routers (DRs) on the source or receiver networks. With
BGP based multicast, PIM may not be running at all, and the FHRs and
LHRs refer to the IGMP/MLD queriers or the Desginated Forwarders
(DFs) elected per [I-D.wijnands-bier-mld-lan-election].
Alternatively, if it is known that a network only has senders then no
IGMP/MLD or DF election is needed - any router may generate SA
routes. That will not cause any issue other than redundant SA routes
being originated.
1.3.4. LAN and Parallel Links
There could be parallel links between two BGP peers. A single multi-
hop session, whether IBGP or EBGP, between loopback addresses may be
used. Except for LAN interfaces in the case of unlabeled (x,G)
unidirectional trees (note that transit LAN interface is not
supported for BGP signaled (*,G) bidirectional tree, and for mLDP
tunnels, traffic on transit LAN is point to point between neighbors),
any link between the two peers can be automatically used by a
downstream peer to receive traffic from the upstream peer, and it is
for the upstream peer to decide which link to use. If one of the
links goes down, the upstream peer switches to a different link and
there is no change needed on the downstream peer.
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For unlabeled (x,G) unidirectional trees, the upstream peer may
prefer LAN interfaces to send traffic (since multiple downstream
peers may be reached simultaneously), or it may make a decision based
on local policy, e.g., for load balancing purposes. Because
different downstream peers might choose different upstream peers for
RPF, when an upstream peer decides to use a LAN interface to send
traffic, it originates an S-PMSI A-D route indicating that one or
more LAN interface will be used. The route carries Route Targets
specific to the LANs so that all the peers on the LANs import the
route. If more than one router originate the route specifying the
same LAN for the same (S,G) or (*,G) flow, then assert procedure
based on the S-PMSI A-D routes happens and assert losers will stop
sending traffic to the LAN.
There may be multiple LAN interfaces between two neighbors, and the
upstream neighbor may send traffic on both LAN interfaces because of
other downstream neighbors on both LANs. In this case, a downstream
neighbor will choose one of the LANs to receive traffic - the RTs in
the S-PMSI route enables the downstream neighbor to determine that
its upstream neighbor is sending on both interfaces and it will only
choose one on which to receive traffic.
1.3.5. Transition
A network currently running PIM can be incrementally transitioned to
BGP based multicast. At any time, a router supporting BGP based
multicast can use PIM with some neighbors (upstream or downstream)
and BGP with some other neighbors. PIM and BGP MUST NOT be used
simultaneously between two neighbors for multicast purposes, and
routers connected to the same LAN MUST be transitioned during the
same maintenance window.
In the case of PIM-SSM, any router can be transitioned at any time
(except on a LAN). It may receive source tree joins from a mixed set
of BGP and PIM downstream neighbors and send source tree joins to its
upstream neighbor using either PIM or BGP signaling.
In the case of PIM-ASM, the RPs are first upgraded to support BGP
based multicast. They learn sources either via PIM procedures from
PIM FHRs, or via Source Active A-D routes from BGP FHRs. In the
former case, the RPs can originate proxy Source Active A-D routes.
There may be a mixed set of RPs/RRs - some capable of both
traditional PIM RP functionalities while some only redistribute SA
routes.
Then any routers can be transitioned incrementally. A transitioned
LHR router will pull Source Active A-D routes from the RPs/RRs when
they receive IGMP/MLD (*,G) joins for ASM groups, and may send either
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PIM (S,G) joins or BGP Source Tree Join routes. A transitioned
transit router may receive (*,G) PIM joins but only send source tree
joins after pulling Source Active A-D routes from RPs/RRs.
Similarly, a network currently running mLDP can be incrementally
transitioned to BGP signaling. Without the complication of ASM, any
router can be transitioned at any time, even without the restriction
of coordinated transition on a LAN. It may receive mixed mLDP label
mapping or BGP updates from different downstream neighbors, and may
exchange either mLDP label mapping or BGP updates with its upstream
neighbors, depending on if the neighbor is using BGP based signaling
or not.
1.3.6. Inter-region Multicast
An end-to-end multicast tree or P2MP tunnel may span multiple
regions, where a region could be an IGP area (or even a sub-area) or
an Autonomous System (AS), and different multicast signaling could be
used in different regions. There are several situations to consider.
1.3.6.1. Inband Signaling across a Region
With inband signaling, the multicast tree/tunnel is signaled through
a region and internal routers in the region maintain corresponding
per-tree/tunnel state. A downstream region and an upstream region
may use the same or different signaling. For example, a (*/s, G) IP
multicast tree with BGP signaling in a downstream region can be
signaled with mLDP Inband Signaling [RFC6826] or with PIM across the
upstream region, and a p2mp tunnel with BGP signaling in the
downstream region can be signaled with mLDP across the upstream
region, or vice versa. A Regional Border Router (RBR) will stitch
the upstream portion (e.g. PIM/mLDP-signaled) to the downstream
portion (e.g. BGP-signaled).
If all routers in the region have routes towards the source/root of
the tree/tunnel then there is nothing different from the intra-region
case. On the other hand, if internal routers do not have routes
towards the source/root, e.g. as with Seamless MPLS
[I-D.ietf-mpls-seamless-mpls], the internal routers need to do RPF
towards an upstream RBR. To signal the RBR information to an
internal upstream router, one of the following ways is used depending
on the signaling method:
* With BGP signaling, the Leaf A-D Route carries a new BGP Extended
Community referred to as Multicast RPF Address EC, similar to PIM
RPF Vector [RFC5496] and mLDP Recursive FEC [RFC6512].
* With PIM signaling, PIM RPF Vector is used.
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* With mLDP signaling, mLDP Recursive FEC is used.
1.3.6.2. Overlay Signaling Over a Region
With overlay signaling, a downstream RBR signals to its upstream RBR
over the region and the internal routers do not maintain the state of
the (overlay) tree/tunnel. This can be done with one of the
following methods:
* mLDP P2MP tunnels can be signaled over the region via targeted LDP
sessions [RFC7060].
* Both IP multicast tree and mLDP P2MP tunnels can be signaled over
a region via BGP-MVPN procedures [RFC6514].
* Both IP multicast tree and mLDP P2MP tunnels can be signaled over
a region via BGP as discussed in the rest of this section.
All three methods are actually very similar in concept. The upstream
RBR tunnels packets to the downstream RBR, just as in the intra-
region case when two routers on the tree/tunnel are not directly
connected. The rest of this section only discusses BGP signaling.
When a downstream RBR determines that the route towards the source/
root has a BGP Next Hop towards a BGP speaker capable of multicast
signaling via BGP as specified in this document, it signals to that
BGP speaker (via a RR or not).
Suppose an upstream RBR receives the signaling for the same tree/
tunnel from several downstream RBRs. It could use Ingress
Replication to replicate packets directly to those downstream RBRs,
or it could use underlay P2MP tunnels instead.
In the latter case, the upstream RBR advertises an S-PMSI A-D route
with a PMSI Tunnel Attribute (PTA) specifying the underlay tunnel.
This is very much like the "mLDP Over Targeted Sessions" [RFC7060] or
BGP-MVPN [RFC6514] (though MCAST-VPN's C-Multicast routes are
replaced with MCAST-TREE's Leaf A-D routes). If the mapping between
overlay tree/tunnel and underlay tunnel is one-to-one, the MPLS Label
field in the PTA is set to 0 or otherwise set to a Domain-wide Common
Block (DCB) label [I-D.ietf-bess-mvpn-evpn-aggregation-label] or an
upstream-assigned label corresponding to the overlay tree/tunnel.
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1.3.6.3. Controller Based Signaling
[I-D.ietf-bess-bgp-multicast-controller] specifies the procedures for
a controller to signal multicast forwarding state to each router on a
multicast tree based on the controller's computation. Depending on
deployment scenarios, in inter-region cases it is possible that the
hop-by-hop signaling specified in this document and the controller
based signaling may be used in different regions.
Consider a situation where an RBR is connected to three regions A, B,
and C, where hop-by-hop signaling is used in A and B, while
controller based signaling is used in C.
For a particular multicast tree, A is the upstream region, while B
and C are two downstream regions. The RBR receives a Leaf A-D route
from region B and a Leaf A-D route from C's controller, and sends a
Leaf A-D route to its upstream router in A.
For a different tree, C is the upstream region while A and B are
downstream. The RBR receives two Leaf A-D routes for the tree from
regions A and B, and one Leaf A-D route from C's controller. Note
that the RBR needs to signal to the controller that it is a leaf of
the tree (because of the Leaf A-D routes received from regions A and
B).
For both cases, the RBR stitches together different segments in
different regions by creating forwarding state based on the Leaf A-D
routes (optionally based on the S-PMSI A-D routes in region A and B
in addition.)
1.3.7. BGP Classful Transport Planes
[I-D.ietf-idr-bgp-ct] specifies an experimental framework for
classifying underlay routes into transport classes and mapping
service routes to specific transport classes. An underlay route
signaled with BGP-CT SAFI carries a Transport Class Route Target (TC-
RT) to both indicate the transport class that the route belongs to
and to control the propagation and importation of the underlay route.
The recipients of the underlay routes use the TC-RT to determine how
the Protocol NH (PNH) is resolved. A service/overlay route may carry
a mapping community that maps to a transport class that is used to
resolve the service route's PNH.
In the case of multicast, the selection of the link/tunnel between an
upstream and downstream tree node may be subject to the transport
class that the tree is for (in the case of an underlay tree) or the
class of transport that the tree should use (in the case of an
overlay tree). In both the underlay and overlay case, the transport
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class is indicated by a mapping community attached to the BGP
multicast routes, which could be a color community or any community
intended for mapping to the transport.
The mapping community not only affects an upstream node's selection
of link/tunnel to a downstream node, but may also affect a downstream
node's selection of its upstream node (i.e. the RPF procedure).
[I-D.ietf-idr-bgp-car] is another experimental mechanism that
provides class/color-aware routing. Multicast signaled by BGP may be
integrated with that as well, but it is outside the scope of this
document.
1.3.8. Flexible Algorithm and Multi-topology
Similar to classful transport, in the case of multi-topology
[RFC4915] [RFC5120] or Flexible Algorithm [RFC9350], a multicast tree
may be required to do RPF based on a particular topology or Flexible
Algorithm (IPA). To signal that, the BGP-MCAST Leaf A-D route may
carry an extended community to encode the topology and/or IPA. Note
that this could also be an operator-defined mapping community that
maps to a transport class (that is associated with a topology or a
Flexible Algorithm).
In the grand scheme of inter-region scenario, if mLDP is to be used
with Flexible Algorithm or Multi-topology for signaling in a
particular region, [I-D.ietf-mpls-mldp-multi-topology] specifies how
topology and/or IPA are encoded.
Similarly, in the case of PIM, [RFC6420] specifies how topology
information is encoded in PIM signaling and a similar mechanism can
be specified for Flexible Algorithm. However, that, and potentially
encoding transport class in PIM/mLDP are outside the scope of this
document.
2. Specification
2.1. BGP NLRIs and Attributes
The BGP Multiprotocol Extensions [RFC4760] allow BGP to carry routes
from multiple different "AFI/SAFIs". This document defines a new
SAFI known as a MCAST-TREE SAFI with value 78 assigned by the IANA.
The MCAST-TREE NLRI defined below is carried in the BGP UPDATE
messages [RFC4271] using the BGP multiprotocol extensions [RFC4760]
with an AFI of IPv4 (1) or IPv6 (2) and a MCAST-TREE SAFI (78).
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The Next hop field of MP_REACH_NLRI attribute SHALL be interpreted as
an IPv4 address whenever the length of the Next Hop address is 4
octets, and as an IPv6 address whenever the length of the Next Hop is
address is 16 octets.
The NLRI field in the MP_REACH_NLRI and MP_UNREACH_NLRI is a prefix
with a maximum length of 12 octets for IPv4 AFI and 36 octets for
IPv6 AFI. The following is the format of the MCAST-TREE NLRI:
+-----------------------------------+
| Route Type (1 octet) |
+-----------------------------------+
| Length (1 octet) |
+-----------------------------------+
| Route Type specific (variable) |
+-----------------------------------+
The Route Type field defines the encoding of the rest of the Route
Type specific MCAST-TREE NLRI.
The Length field indicates the length in octets of the Route Type
specific field of MCAST-TREE NLRI.
The following new route types are defined:
3 - S-PMSI A-D Route for (x,G)
4 - Leaf A-D Route
5 - Source Active A-D Route
0x43 - S-PMSI A-D Route for mLDP
Except for the Source Active A-D routes, the routes are to be
consumed by targeted upstream/downstream neighbors and are not
propagated further. This can be achieved by outbound filtering based
on the RTs that lead to the importation of the routes.
The Type-3/4 routes MAY carry a Tunnel Encapsulation Attribute (TEA)
[RFC9012]. The Type-0x43 route MUST carry a TEA. When used for
mLDP, the Type-4 route MUST carry a TEA. The TEA includes one tunnel
entry with an MPLS Label Stack Sub-TLV that includes one label. This
is the label associated with the (x,G) labeled tree or mLDP tunnel.
2.1.1. S-PMSI A-D Route
Similar to defined in RFC 6514, an S-PMSI A-D Route Type specific
MCAST-TREE NLRI consists of the following:
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+-----------------------------------+
| RD (8 octets) |
+-----------------------------------+
| Multicast Source Length (1 octet) |
+-----------------------------------+
| Multicast Source (variable) |
+-----------------------------------+
| Multicast Group Length (1 octet) |
+-----------------------------------+
| Multicast Group (variable) |
+-----------------------------------+
| Upstream Router's IP Address |
+-----------------------------------+
If the Multicast Source (or Group) field contains an IPv4 address,
then the value of the Multicast Source (or Group) Length field is 32.
If the Multicast Source (or Group) field contains an IPv6 address,
then the value of the Multicast Source (or Group) Length field is
128.
Usage of other values of the Multicast Source Length and Multicast
Group Length fields is outside the scope of this document.
There are three usages for S-PMSI A-D route. They're described in
Section 1.3.6.2, Section 2.2.5 and Section 2.2.6 respectively.
2.1.2. Leaf A-D Route
Similar to the Leaf A-D route in [RFC6514], a MCAST-TREE Leaf A-D
route's route key includes the corresponding S-PMSI NLRI, plus the
Originating Router's IP Address.
+-----------------------------------+
| S-PMSI NLRI |
+-----------------------------------+
| Originating Router's IP Address |
+-----------------------------------+
For example, the entire NLRI of a Leaf A-D route for (x,G) tree is as
following:
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+- +-----------------------------------+
| | Route Type - 4 (Leaf A-D) |
| +-----------------------------------+
| | Length (1 octet) |
| +- +-----------------------------------+ --+
| | | Route Type - 3 (S-PMSI A-D) | |
L | L | +-----------------------------------+ | S
E | E | | Length (1 octet) | | |
A | A | +-----------------------------------+ | P
F | F | | RD (8 octets) | | M
| | +-----------------------------------+ | S
| | | Multicast Source Length (1 octet) | | I
| | +-----------------------------------+ | I
N | R | | Multicast Source (variable) | |
L | O | +-----------------------------------+ |
R | U | | Multicast Group Length (1 octet) | | N
I | T | +-----------------------------------+ | L
| E | | Multicast Group (variable) | | R
| | +-----------------------------------+ | I
| K | | Upstream Router's IP Address | |
| E | +-----------------------------------+ --+
| Y | | Originating Router's IP Address |
+- +- +-----------------------------------+
2.1.3. Source Active A-D Route
Similar to what is defined in [RFC6514], a Source Active A-D Route
Type specific MCAST NLRI consists of the following:
+-----------------------------------+
| RD (8 octets) |
+-----------------------------------+
| Multicast Source Length (1 octet) |
+-----------------------------------+
| Multicast Source (variable) |
+-----------------------------------+
| Multicast Group Length (1 octet) |
+-----------------------------------+
| Multicast Group (variable) |
+-----------------------------------+
The definition of the source/length and group/length fields are the
same as in the S-PMSI A-D routes.
Usage of Source Active A-D routes is described in Section 1.3.1.1.
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2.1.4. S-PMSI A-D Route for mLDP
The route is used to signal upstream FEC for an MP2MP mLDP tunnel.
The route key include a Route Distinguisher, the mLDP FEC and the
Upstream Router's IP Address field.
2.1.5. Session Address Extended Community
For two BGP speakers to determine if they are directly connected,
each will advertise their local interface addresses, with a Session
Address Extended Community. This is an IPv4/IPv6 Address Specific EC
with the Global Administrator Field set to the local address used for
its multihop sessions and the Local Administrator Field set to the
prefix length corresponding to the interface's network mask.
As an IPv4 example, a router has two interfaces with address
192.0.2.1/28 and 198.51.100.1/24 respectively (notice the different
prefix lengths), and a loopback address 203.0.113.1/32 that is used
for BGP sessions. It advertises prefix 192.0.2.1/32 with a Session
Address EC 203.0.113.1:28 and 198.51.100.1/32 with a Session Address
EC 203.0.113.1:24. If it also uses another loopback address
203.0.113.101/32 for other BGP sessions, then the routes will
additionally carry Session Address EC 203.0.113.101:28 and
203.0.113.101:24 respectively.
As an IPv6 example, a router has two interfaces with address
2001:DB8::1:1/112 and 2001:DB8::2:1/120 respectively (notice the
different prefix lengths), and a loopback address 2001:DB8::3:1/128
that is used for BGP sessions. It advertises prefix
2001:DB8::1:1/128 with a Session Address EC "2001:DB8::3:1":112 (the
quoted part is the IPv6 address for the Global Administrator field
and the "112" is the Local Administrator field) and prefix
2001:DB8::2:1/128 with a Session Address EC "2001:DB8::3:1":120. If
it also uses another loopback address 2001:DB8:3:101/128 for other
BGP sessions, then the routes will additionally carry Session Address
EC "2001:DB8::3:101":112 and "2001:DB8::3:101":120 respectively.
This achieves what the Address List TLV in LDP Address Messages
achieves, and can also be used to indicate that a router supports the
BGP multicast signaling procedures specified in this document.
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Only those interface addresses that will be used as resolved RPF
nexthops in the RIB need to be advertised with the Session Address
EC. For example, the RPF lookup may say that the resolved nexthop
address is A1, so the router needs to find out the corresponding BGP
speaker with address A1 through the (interface address, session
address) mapping built according to the interface address NLRI with
the Session Address EC. For comparison, in LDP this is done via the
(interface address, session address) mapping that is built by the LDP
Address Messages.
2.1.6. Multicast RPF Address Extended Community
This is an IP or IPv6 Address Specific EC with the Global Admin Field
set to the address of the upstream RBR and the Local Admin Field set
to 0.
2.1.7. Topology/IPA Extended Community
This is a Transitive Opaque Extended Community with the following
format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x03 | Sub-Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPA | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPA is the Flexible Algorithm number and MT-ID is the Multi-Topology
Identifier to be used for setting a multicast tree. The usage of
this EC is described in Section 1.3.8.
2.2. Procedures
2.2.1. Source Discovery for ASM
When an FHR first receives a multicast packet addressed to an ASM
group, it originates a Source Active route.
The FHRs withdraw the Source Active route after a certain amount of
time since it last received a packet of an (S,G) flow. The amount of
time to wait is a local matter.
The SA routes carry an IPv4 or IPv6 address specific Route Target.
The Global Administrator field is set to the group address of the
flow, and the Local Administrator field is set to 0 or a pre-assigned
domain-wide unique value that identifies a VPN.
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When an LHR needs to join an ASM group (e.g., as the result of
receiving a (*,G) IGMP/MLD join), it advertises a Route Target
Membership route, with the Route Target field in the NLRI set
according to the group, as how an FHR encodes the Route Target in its
Source Active routes. The propagation of the SA routes is subject to
cooperative export filtering as specified in [RFC4684] and referred
to as Route Target Constrain (RTC) mechanism in this document. With
that, the LHR only receives Source Active routes for groups that it
is interested in.
Upon the receiving of the Source Active A-D routes, the LHR
originates Leaf A-D routes as described below, as long as it still
needs to receive traffic for the flows (i.e., the corresponding IGMP/
MLD membership exists or join from downstream PIM/BGP neighbor
exists).
2.2.2. Originating Tree Join Routes
2.2.2.1. (x,G) Multicast Tree
When a router needs to join a particular (S,G) tree, it determines
the RPF nexthop address wrt the source, following the same RPF
procedures as defined for PIM. It further finds the BGP router that
advertised the nexthop address as one of its local addresses.
If the RPF neighbor supports MCAST-TREE SAFI, this router originates
a Leaf A-D route. Although it is unsolicited, it is constructed as
if there was a corresponding S-PMSI A-D route. The Upstream Router's
IP Address field is set to the RPF neighbor's session address (learnt
via the EC attached to the host route for the RPF nexthop address).
An Address Specific RT corresponding to the session address is
attached to the route, with the Global Administrative Field set to
the session address and the local administrative field set to 0 or a
pre-assigned domain-wide unique value that identifies a VPN. The
route is advertised the route to the RPF neighbor (in the case of
EBGP or hop-by-hop IBGP), or to one or more RRs.
Similarly, when a router learns that it needs to join a bi-
directional tree for a particular group, it determines the RPF
neighbor wrt the RPA. If the neighbor supports MCAST-TREE SAFI, it
originates a Leaf A-D Route.
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As the Leaf A-D route is originated, the router sets up the
corresponding forwarding state such that the expected incoming
interface list includes all non-LAN interfaces directly connecting to
the upstream neighbor. LAN interfaces are added upon receiving
corresponding S-PMSI A-D route (Section 2.2.5.2). If the upstream
neighbor is not directly connected, a corresponding S-PMSI A-D route
advertised by the upstream router is used to determine the tunnel
used to receive traffic, as described in Section 1.3.6.2
When the upstream neighbor changes, the previously advertised Leaf
A-D route is withdrawn. If there is a new upstream neighbor, a new
Leaf A-D route is originated, corresponding to the new neighbor.
Because NLRIs are different for the old and new Leaf A-D routes,
make-before-break as well as Multicast Only Fast ReRroute (MoFRR)
[RFC7431] can be achieved.
2.2.2.2. BGP Inband Signaling for mLDP Tunnel
The same mLDP procedures as defined in [RFC6388] are followed, except
that where a label mapping message is sent in [RFC6388], a Leaf A-D
route is sent if the upstream neighbor supports BGP based signaling.
2.2.3. Receiving Tree Join Routes
A router (auto-)configures Import RTs matching itself so that it can
import tree join routes from their peers. Note that in this
document, tree join routes are Leaf A-D routes.
When a router receives a tree join route and imports it, it
determines if it needs to originate its own corresponding route and
advertise further upstream wrt the source/RPA or mLDP tunnel root.
If this router is the FHR or is on the RPL for a bidrectional group,
or is the tunnel root, then it does not need to. Otherwise, the
procedures in Section 2.2.2 are followed.
Additionally, the router sets up its corresponding forwarding state
such that traffic will be sent to the downstream neighbor, and
received from the downstream neighbor in the case of bidirectional
tree/tunnel. If the downstream neighbor is not directly connected,
the tunnel announced in a corresponding S-PMSI route is used, as
described in Section 1.3.6.2.
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2.2.4. Withdrawal of Tree Join Routes
For a particular tree or tunnel, if a downstream neighbor withdraws
its Leaf A-D route, the neighbor is removed from the corresponding
forwarding state. If all downstream neighbors withdraw their tree
join routes and this router no longer has local receivers, it
withdraws the tree join routes that it previously originated.
As mentioned earlier, when the upstream neighbor changes, the
previously advertised Leaf A-D route is also withdrawn. The
corresponding incoming interfaces are also removed from the
corresponding forwarding state.
2.2.5. LAN procedures for (x,G) Unidirectional Tree
For a unidirectional (x,G) multicast tree, if there is a LAN
interface connecting to the downstream neighbor, it MAY be preferred
over non-LAN interfaces, but an S-PMSI A-D route MUST be originated
to facilitate the analog of the Assert process (Section 2.2.5.1).
2.2.5.1. Originating S-PMSI A-D Routes
If this router chooses to use a LAN interface to send traffic to its
neighbors for a particular (S,G) or (*,G) flow, it MUST announce that
by originating a corresponding S-PMSI A-D route that does not include
a PTA. The LAN interface is identified by an IP address specific RT,
with the Global Administrative Field set to the LAN interface's
address prefix and the Local Administrative Field set to the prefix
length. The RT also serves the purpose of restricting the importing
of the route by all routers on the LAN. An operator MUST ensure that
RTs encoded as above are not used for other purposes. Practically
that should not be unreasonable.
If multiple LAN interfaces are to be used (to reach different sets of
neighbors), then the route will include multiple RTs, one for each
used LAN interface as described above.
2.2.5.2. Receiving S-PMSI A-D Routes
A router (auto-)configures an Import RT for each of its LAN
interfaces over which BGP is used for multicast signaling. The
construction of the RT is described in the previous section.
When a router R1 imports an S-PMSI A-D route for flow (x,G) from
router R2, R1 checks to see if it also originats an S-PMSI A-D route
with the same NLRI except the Upstream Router's IP Address field.
When a router R1 originates an S-PMSI A-D route, it checks to see if
it also has installed an S-PMSI A-D route, from some other router R2,
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with the same NLRI except the Upstream Router's IP Address field. In
either case, R1 checks to see if the two routes have an RT in common
and the RT is encoded as in Section 2.2.5.1. If so, then there is a
LAN attached to both R1 and R2, and both routers are prepared to send
(S,G) traffic onto that LAN. This kicks off the assert procedure to
elect a winner - the one with the highest Upstream Router's IP
Address in the NLRI wins. An assert loser will not include the
corresponding LAN interface in its outgoing interface list, but it
keeps the S-PMSI A-D route that it originates.
If this router does not have a matching S-PMSI route of its own with
some common RTs, and the originator of the received S-PMSI route is a
chosen upstream neighbor for the corresponding flow, then this router
updates its forwarding state to include the LAN interface in the
incoming interface list. When the last S-PMSI route with a RT
matching the LAN is withdrawn later, the LAN interface is removed
from the incoming interface list.
Note that a downstream router on the LAN does not participate in the
assert procedure. It adds/keeps the LAN interface in the expected
incoming interfaces as long as its chosen upstream peer originates
the S-PMSI AD route. It does not switch to the assert winner as its
upstream. An assert loser MAY keep sending joins upstream based on
local policy even if it has no other downstream neighbors (this could
be used for fast switchover in case the assert winner fails).
If this router receives an S-PMSI A-D route from its upstream
neighbor with multiple RTs for the LANs that this router is on, it
MUST select only one of the LAN interfaces to receive traffic. Which
LAN interface is selected is a local decision.
2.2.6. Distributing Label for Upstream Traffic for Bidirectional Tree/
Tunnel
For MP2MP mLDP tunnels or labeled (*,G) bidirectional trees, an
upstream router needs to advertise a label to all its downstream
neighbors so that the downstream neighbors can send traffic to
itself.
For MP2MP mLDP tunnels, the same procedures for mLDP are followed
except that instead of MP2MP-U Label Mapping messages, S-PMSI A-D
Routes for mLDP are used.
For labeled (*,G) bidirectional trees, for a Leaf A-D route received
from a downstream neighbor, a corresponding S-PMSI A-D route is sent
back to the downstream router.
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In both cases, a single S-PMSI A-D route is originated for each tree
from this router, but with multiple RTs (one for each downstream
neighbor on the tree). A TEA specifies a label allocated by the
upstream router for its downstream neighbors to send traffic with.
Note that this is still a "downstream allocated" label (the upstream
router is "downstream" from traffic direction point of view).
The S-PMSI routes do not carry a PTA, unless a tunnel is used to
reach downstream neighbors as described in Section 1.3.6.2.
3. IANA Considerations
IANA has assigned BGP SAFI value 78 for the MCAST-TREE SAFI.
This document requests IANA to create a new "BGP MCAST-TREE Route
Types" registry, referencing this document. The following initial
values are defined:
0~2 - Reserved
3 - S-PMSI A-D Route for (x,G)
4 - Leaf A-D Route
5 - Source Active A-D Route
0x43 - S-PMSI A-D Route for mLDP
This document requests IANA to assign two Sub-type values from
Transitive IPv4-Address-Specific Extended Community Sub-types
Registry for Session Address EC and Multicast RPF Address EC
respectively.
This document requests IANA to assign two Sub-Type values from
Transitive IPv6-Address-Specific Extended Community Types Registry
for Session Address EC and Multicast RPF Address EC respectively.
This document requests IANA to assign one Sub-Type value from
Transitive Opaque Extended Community Types Registry for the Topology/
IPA EC.
4. Security Considerations
This document shares many of the mechanisms and concepts of MVPN and,
accordingly, can reuse many of the security considerations described
in RFC6513 and RFC6514, though the distinctions made on PE-CE links
and relationships in those documents are not relevant.
This document describes interworking with several multicast control
protocols, including PIM-SM, PIM-SSM, PIM-Bidir, mLDP and IGMP/MLD.
Security considerations specified for those protocols are applicable
to this document.
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Implementations should include Multicast Damping procedures specified
in RFC7899 to protect the control plane from excessive churn due to
multicast dynamicity. Implementations should also include the
ability to rate-limit join state creation on a per-peer and per-RIB
basis, as well as rate-limit Source Active A-D route propagation on a
per-source, per-peer and per-RIB basis to configurable thresholds.
5. Acknowledgements
The authors thank Marco Rodrigues for his initial idea/ask of using
BGP for multicast signaling beyond MVPN. We thank Eric Rosen for his
questions, suggestions, and help to find solutions to some issues.
We also thank Luay Jalil, James Uttaro and Shraddha Hegde for their
comments and support for the work. Special thanks go to Joe Halpern
for his thorough review and comments that significantly improved the
document quality.
6. References
6.1. Normative References
[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>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
November 2006, <https://www.rfc-editor.org/info/rfc4684>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007,
<https://www.rfc-editor.org/info/rfc5015>.
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[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <https://www.rfc-editor.org/info/rfc5492>.
[RFC6388] Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
Thomas, "Label Distribution Protocol Extensions for Point-
to-Multipoint and Multipoint-to-Multipoint Label Switched
Paths", RFC 6388, DOI 10.17487/RFC6388, November 2011,
<https://www.rfc-editor.org/info/rfc6388>.
[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>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[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>.
[RFC9012] Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
"The BGP Tunnel Encapsulation Attribute", RFC 9012,
DOI 10.17487/RFC9012, April 2021,
<https://www.rfc-editor.org/info/rfc9012>.
6.2. Informative References
[I-D.ietf-bess-bgp-multicast-controller]
Zhang, Z. J., Raszuk, R., Pacella, D., and A. Gulko,
"Controller Based BGP Multicast Signaling", Work in
Progress, Internet-Draft, draft-ietf-bess-bgp-multicast-
controller-11, 21 August 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
bgp-multicast-controller-11>.
[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>.
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[I-D.ietf-bess-mvpn-pe-ce]
Patel, K., Rosen, E. C., and Y. Rekhter, "BGP as an MVPN
PE-CE Protocol", Work in Progress, Internet-Draft, draft-
ietf-bess-mvpn-pe-ce-01, 5 October 2015,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
mvpn-pe-ce-01>.
[I-D.ietf-idr-bgp-car]
Rao, D., Agrawal, S., and Co-authors, "BGP Color-Aware
Routing (CAR)", Work in Progress, Internet-Draft, draft-
ietf-idr-bgp-car-04, 14 November 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
car-04>.
[I-D.ietf-idr-bgp-ct]
Vairavakkalai, K. and N. Venkataraman, "BGP Classful
Transport Planes", Work in Progress, Internet-Draft,
draft-ietf-idr-bgp-ct-18, 5 November 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
ct-18>.
[I-D.ietf-mpls-mldp-multi-topology]
Wijnands, I., Mishra, M. P., Raza, S., Budhiraja, A.,
Zhang, Z. J., and A. Gulko, "mLDP Extensions for Multi-
Topology Routing", Work in Progress, Internet-Draft,
draft-ietf-mpls-mldp-multi-topology-03, 2 August 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mldp-multi-topology-03>.
[I-D.ietf-mpls-seamless-mpls]
Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
M., and D. Steinberg, "Seamless MPLS Architecture", Work
in Progress, Internet-Draft, draft-ietf-mpls-seamless-
mpls-07, 28 June 2014,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
seamless-mpls-07>.
[I-D.wijnands-bier-mld-lan-election]
Wijnands, I., Pfister, P., and Z. J. Zhang, "Generic
Multicast Router Election on LAN's", Work in Progress,
Internet-Draft, draft-wijnands-bier-mld-lan-election-02,
19 October 2023, <https://datatracker.ietf.org/doc/html/
draft-wijnands-bier-mld-lan-election-02>.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, DOI 10.17487/RFC3376, October 2002,
<https://www.rfc-editor.org/info/rfc3376>.
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[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<https://www.rfc-editor.org/info/rfc4915>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
[RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path
Forwarding (RPF) Vector TLV", RFC 5496,
DOI 10.17487/RFC5496, March 2009,
<https://www.rfc-editor.org/info/rfc5496>.
[RFC6420] Cai, Y. and H. Ou, "PIM Multi-Topology ID (MT-ID) Join
Attribute", RFC 6420, DOI 10.17487/RFC6420, November 2011,
<https://www.rfc-editor.org/info/rfc6420>.
[RFC6512] Wijnands, IJ., Rosen, E., Napierala, M., and N. Leymann,
"Using Multipoint LDP When the Backbone Has No Route to
the Root", RFC 6512, DOI 10.17487/RFC6512, February 2012,
<https://www.rfc-editor.org/info/rfc6512>.
[RFC6559] Farinacci, D., Wijnands, IJ., Venaas, S., and M.
Napierala, "A Reliable Transport Mechanism for PIM",
RFC 6559, DOI 10.17487/RFC6559, March 2012,
<https://www.rfc-editor.org/info/rfc6559>.
[RFC6826] Wijnands, IJ., Ed., Eckert, T., Leymann, N., and M.
Napierala, "Multipoint LDP In-Band Signaling for Point-to-
Multipoint and Multipoint-to-Multipoint Label Switched
Paths", RFC 6826, DOI 10.17487/RFC6826, January 2013,
<https://www.rfc-editor.org/info/rfc6826>.
[RFC7060] Napierala, M., Rosen, E., and IJ. Wijnands, "Using LDP
Multipoint Extensions on Targeted LDP Sessions", RFC 7060,
DOI 10.17487/RFC7060, November 2013,
<https://www.rfc-editor.org/info/rfc7060>.
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[RFC7431] Karan, A., Filsfils, C., Wijnands, IJ., Ed., and B.
Decraene, "Multicast-Only Fast Reroute", RFC 7431,
DOI 10.17487/RFC7431, August 2015,
<https://www.rfc-editor.org/info/rfc7431>.
[RFC7438] Wijnands, IJ., Ed., Rosen, E., Gulko, A., Joorde, U., and
J. Tantsura, "Multipoint LDP (mLDP) In-Band Signaling with
Wildcards", RFC 7438, DOI 10.17487/RFC7438, January 2015,
<https://www.rfc-editor.org/info/rfc7438>.
[RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of
BGP for Routing in Large-Scale Data Centers", RFC 7938,
DOI 10.17487/RFC7938, August 2016,
<https://www.rfc-editor.org/info/rfc7938>.
[RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
DOI 10.17487/RFC9350, February 2023,
<https://www.rfc-editor.org/info/rfc9350>.
Authors' Addresses
Zhaohui Zhang
Juniper Networks
Email: zzhang@juniper.net
Lenny Giuliano
Juniper Networks
Email: lenny@juniper.net
Keyur Patel
Arrcus
Email: keyur@arrcus.com
IJsbrand Wijnands
Arrcus
Email: ice@braindump.be
Mankamana Mishra
Cisco Systems
Email: mankamis@cisco.com
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Arkadiy Gulko
EdwardJones
Email: arkadiy.gulko@edwardjones.com
Zhang, et al. Expires 4 June 2024 [Page 31]
