L3VPN Working Group Yakov Rekhter (Editor)
Internet Draft Juniper Networks
Intended Status: Standards Track
Expires: January 4, 2015 Eric Rosen (Editor)
Updates: 6513,6514,6625 Cisco Systems
Rahul Aggarwal
Arktan
Yiqun Cai
Microsoft
Wim Henderickx
Alcatel-Lucent
Thomas Morin
France Telecom - Orange
Praveen Muley
Alcatel-Lucent
Ray Qiu
Juniper Networks
IJsbrand Wijnands
Cisco Systems
July 4, 2014
Extranet Multicast in BGP/IP MPLS VPNs
draft-ietf-l3vpn-mvpn-extranet-05.txt
Abstract
Previous RFCs specify the procedures necessary to allow IP multicast
traffic to travel from one site to another within a BGP/MPLS IP VPN
(Virtual Private Network). However, it is sometimes desirable to
allow multicast traffic whose source is in one VPN to be received by
systems that are in another VPN. This is known as a "Multicast VPN
(MVPN) extranet". This document updates RFCs 6513, 6514, and 6625 by
specifying the procedures that are necessary in order to provide MVPN
extranet service.
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Status of this Memo
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document authors. All rights reserved.
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Table of Contents
1 Introduction .......................................... 4
1.1 Terminology ........................................... 5
1.2 Scope ................................................. 7
1.2.1 Customer Multicast Control Protocols .................. 7
1.2.2 Provider Multicast Control Protocols .................. 8
1.3 Clarification on Use of Route Distinguishers .......... 8
1.4 Overview .............................................. 9
2 Extranets and Overlapping Address Spaces .............. 11
2.1 Ambiguity: P-tunnel with Extranet/Non-Extranet Flows .. 13
2.2 Ambiguity: P-tunnel with Multiple Extranet Flows ...... 15
2.3 Preventing Misdelivery in These Scenarios ............. 18
2.3.1 Do Not Deliver Packets from the 'Wrong' P-tunnel ...... 18
2.3.2 Policies to Prevent Ambiguity on a P-tunnel ........... 20
3 Extranet Transmission Models .......................... 21
3.1 Transmitting an Extranet C-flow on a Single PMSI ...... 21
3.1.1 Without Extranet Separation ........................... 22
3.1.2 With Extranet Separation .............................. 22
3.2 Transmitting an Extranet C-flow over Multiple PMSIs ... 23
4 Distribution of Routes that Match C-S/C-RP Addresses .. 23
4.1 UMH-Eligible Routes ................................... 23
4.1.1 Extranet Separation ................................... 24
4.2 Distribution of Unicast Routes Matching C-RPs and DRs . 24
4.3 Route Targets and Ambiguous UMH-Eligible Routes ....... 25
4.4 Dynamically Marking Extranet Routes ................... 27
4.4.1 The Extranet Source Extended Community ................ 27
4.4.2 Distribution of Extranet Source Extended Community .... 28
4.5 The 'Extranet Separation' Extended Community .......... 29
5 Origination and Distribution of BGP A-D Routes ........ 29
5.1 Route Targets of UMH-eligible Routes and A-D Routes ... 29
5.2 Considerations for Particular Inclusive Tunnel Types .. 32
5.2.1 RSVP-TE P2MP .......................................... 32
5.2.2 Ingress Replication ................................... 32
6 When PIM is the PE-PE C-multicast Control Plane ....... 33
6.1 Provisioning VRFs with RTs ............................ 34
6.1.1 Incoming and Outgoing Extranet RTs .................... 34
6.1.2 UMH-eligible Routes and RTs ........................... 35
6.1.3 PIM C-Instance Reverse Path Forwarding Determination .. 35
6.2 Single PMSI per C-flow Model .......................... 36
6.2.1 Forming the MI-PMSIs .................................. 36
6.2.2 S-PMSIs ............................................... 39
6.2.3 Sending PIM Control Packets ........................... 40
6.2.4 Receiving PIM Control Packets ......................... 41
6.2.5 Sending and Receiving Data Packets .................... 41
6.3 Multiple PMSIs per C-flow Model ....................... 41
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6.3.1 Forming the MI-PMSIs .................................. 42
7 When BGP is the PE-PE C-multicast Control Plane ....... 44
7.1 Originating C-multicast Routes ........................ 44
7.2 Originating A-D Routes Without Extranet Separation .... 45
7.2.1 Intra-AS I-PMSI A-D Routes ............................ 45
7.2.2 S-PMSI A-D Routes ..................................... 45
7.2.3 Source Active A-D Routes .............................. 46
7.2.3.1 When Inter-Site Shared Trees Are Used ................. 46
7.2.3.2 When Inter-Site Shared Trees Are Not Used ............. 47
7.3 Originating A-D Routes With Extranet Separation ....... 47
7.3.1 Intra-AS I-PMSI A-D Routes ............................ 47
7.3.2 S-PMSI A-D Routes ..................................... 48
7.3.3 Source Active A-D Routes .............................. 49
7.4 Determining the Expected P-tunnel for a C-flow ........ 50
7.4.1 (C-S,C-G) S-PMSI A-D Routes ........................... 52
7.4.2 (C-S,C-*) S-PMSI A-D Routes ........................... 52
7.4.3 (C-*,C-G) S-PMSI A-D Routes ........................... 52
7.4.4 (C-*,C-*) S-PMSI A-D Routes ........................... 54
7.4.5 I-PMSI A-D Routes ..................................... 54
7.5 Packets Arriving from the Wrong P-tunnel .............. 55
8 Multiple Extranet VRFs on the same PE ................. 55
9 IANA Considerations ................................... 56
10 Security Considerations ............................... 56
11 Acknowledgments ....................................... 58
12 Authors' Addresses .................................... 58
13 References ............................................ 59
13.1 Normative References .................................. 59
13.2 Informative References ................................ 60
1. Introduction
Previous RFCs ([MVPN], [MVPN-BGP]) specify the procedures necessary
to allow IP multicast traffic to travel from one site to another
within a BGP/MPLS IP VPN (Virtual Private Network). However, it is
sometimes desirable to allow multicast traffic whose source is in one
VPN to be received by systems that are in another VPN. This is known
as an "extranet MVPN". This document specifies the procedures that
are necessary in order to provide Extranet MVPN functionality.
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1.1. Terminology
This document uses terminology from [MVPN], and in particular uses
the prefixes "C-" and "P-" as specified in Section 3.1 of [MVPN], and
"A-D routes" for "auto-discovery routes".
The term "Upstream Multicast Hop" (UMH) is used as defined in [MVPN].
The term "UMH-eligible route" is used to mean "route eligible for UMH
determination", as defined in Section 5.1.1 of [MVPN]. We will say
that a given UMH-eligible route or unicast route "matches" a given IP
address, in the context of a given Virtual Routing and Forwarding
Table (VRF), if the address prefix of the given route is the longest
match in that VRF for the given IP address. We will sometimes say
that a route "matches" a particular host if the route matches an IP
address of the host.
We follow the terminology of section 3.2 of [MVPN-WILDCARDS] when
talking of an S-PMSI A-D route being "installed". That is, we say
that an S-PMSI A-D route is "installed" (in a given VRF) if it has
been selected by the BGP decision process as the preferred route for
its NLRI. We also follow the terminology of section 3.2 of [MVPN-
WILDCARDS] when saying that an S-PMSI A-D route has been "originated
by a given PE"; this means that the given PE's IP address is
contained in the "Originating Router's IP Address" field in the NLRI
of the route.
We use the following additional terminology and notation:
- Extranet C-source: a multicast source, in a given VPN, that is
allowed by policy to send multicast traffic to receivers that are
in other VPNs.
- Extranet C-receiver: a multicast receiver, in a given VPN, that
is allowed by policy to receive multicast traffic from extranet
C-sources that are in other VPNs.
- Extranet C-flow: a multicast flow (with a specified C-source
address and C-group address) whose source is an extranet
C-source, and which is allowed by policy to have extranet
C-receivers.
- Extranet C-group: a multicast group address that is in the "Any
Source Multicast" (ASM) group address range, and that is allowed
by policy to have Extranet C-sources and Extranet C-receivers
that are not all in the same VPN. Note that we will sometimes
refer to "SSM C-group addresses" (i.e., to C-group addresses in
the SSM group address range), but will never call them "extranet
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C-groups".
N.B.: Any source of traffic for an extranet C-group is considered
to be an extranet C-source, and any receiver of traffic addressed
to an extranet C-group is considered to be an extranet
C-receiver.
- Extranet C-RP: a multicast Rendezvous Point (RP) for an extranet
C-group; it is allowed by policy to receive PIM register messages
[PIM] from outside its VPN, and to send multicast data packets to
extranet C-receivers outside its VPN.
- Host(C-S,A): the host (or if C-S is an "anycast address", the set
of hosts) denoted by the address C-S in the context of VPN-A.
For example, if a particular C-source in VPN A has address C-S,
then Host(C-S,A) refers to that C-source.
- SAFI-n route: a BGP route whose Address Family Identifier (AFI)
is either 1 (IPv4) or 2 (IPv6), and whose Subsequent Address
Family Identifier (SAFI) is "n".
Note that a given extranet C-source is not necessarily allowed to
transmit to every extranet C-receiver; policy determines which
extranet C-sources are allowed to transmit to which extranet
C-receivers. However, in the case of an extranet (ASM) C-group, all
transmitters to the group are allowed to transmit to all the
receivers of the group, and all the receivers of the group are
allowed to receive from all transmitters to the group.
We say that a given VRF "contains" or "has" a multicast C-source (or
that the C-source is "in" the VRF), if that C-source is in a site
connected to that VRF, and the VRF originates a UMH-eligible route
(see Section 4) that matches the address of the C-source.
We say that a given VRF "contains" or "has" a multicast C-receiver
(or that the C-receiver is "in" the VRF), if that C-receiver is in a
site connected to that VRF.
We say that a given VRF "contains" or "has" the C-RP for a given ASM
group (or that the C-RP is "in" the VRF) if that C-RP is in a site
connected to that VRF, and the VRF originates a unicast route and a
(possibly different, possibly the same) UMH-eligible route (see
Section 4) whose respective address prefixes match the C-RP address.
[MVPN] allows a set of "Provider tunnels" (P-tunnels) to be
aggregated together and transported via an outer P-tunnel, i.e., it
allows for the use of hierarchical Label Switched Paths (LSPs) as
P-tunnels. A two-level hierarchical LSP, for example, can be thought
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of as a set of "inner tunnels" aggregated into an outer tunnel. In
this document, when we speak of a P-tunnel, we are always speaking of
the innermost P-tunnel, i.e., of a P-tunnel at the lowest level of
hierarchy. P-tunnels are identified in the Provider Multicast
Service Interface (PMSI) Tunnel Attributes (PTAs) [MVPN-BGP] of BGP
Auto-Discovery (A-D) routes. Two PTAs that have the same Tunnel Type
and Tunnel Identifier fields, but different MPLS label fields, are
thus considered to identify two different P-tunnels. (I.e., for the
purposes of this document, the MPLS label included in the PTA, if
any, is considered to be part of the tunnel identifier.)
We say that the NLRI of a BGP S-PMSI A-D route or Source Active A-D
route contains (C-S,C-G) if its "Multicast Source" field contains C-S
and its "Multicast Group" field contains C-G. If either or both of
these fields is encoded as a wildcard, we will say that the NLRI
contains (C-*,C-*) (both fields encoded as wildcard), or (C-*,C-G)
(multicast source field encoded as wildcard) or (C-S,C-*) (multicast
group field encoded as wildcard).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL", when and only when appearing in all capital letters, are
to be interpreted as described in [RFC2119].
1.2. Scope
1.2.1. Customer Multicast Control Protocols
This document presumes that the VPN customer is using "PIM Sparse
Mode", operating in either "Source-Specific Mode" (SSM) or "Any
Source Mode" (ASM), as the multicast control protocol at the customer
sites. Support for other customer IP multicast control protocols
(e.g., [BIDIR-PIM], PIM "Dense Mode") is outside the scope of this
document. Support for the customer use of MPLS multicast control
protocols (e.g., [mLDP], [RSVP-P2MP]) is also outside the scope of
this document.
When a VPN customer uses ASM, the customer routers need to be able to
map from a C-group address to a C-RP address. These mappings can be
provisioned in each router, or can be discovered dynamically through
protocols such as BSR [BSR]. However, it cannot be assumed that such
protocols will automatically work in the context of an extranet.
Discussion of the use of such protocols in an extranet is outside the
scope of this document.
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1.2.2. Provider Multicast Control Protocols
[MVPN] allows either PIM or BGP to be used as the protocol for
distributing customer multicast routing information. Except where
otherwise specified, such as in Sections 6 and 7, the procedures of
this document cover both cases.
1.3. Clarification on Use of Route Distinguishers
[L3VPN] requires that every VRF be associated with one or more Route
Distinguishers (RD). Each VPN-IPv4 or VPN-IPv6 route that is
exported from a particular VRF contains, in its NLRI, an RD that is
associated with that VRF.
[L3VPN] allows a given RD to be associated with more than one VRF, as
long as all the VRFs associated with that RD belong to the same VPN.
However, in the most common deployment model, each RD is associated
with one and only one VRF. [MVPN] and [MVPN-BGP] presuppose this
deployment model. That is, [MVPN] and [MVPN-BGP] presuppose that
every RD is associated with one and only one VRF. We will call this
the "unique VRF per RD" condition.
[MVPN-BGP] defines the MCAST-VPN address family, which has a number
of route types. Each Intra-AS I-PMSI A-D route, S-PMSI A-D route,
and Source Active A-D route, when exported from a given VRF,
contains, in its NLRI, an RD that is associated with the VRF.
[MVPN] and [MVPN-BGP] also discuss a class of routes known as "UMH-
eligible" routes; when a UMH-eligible route is exported from a given
VRF, its NLRI contains an RD of the VRF.
[MVPN-BGP] also defines MCAST-VPN routes whose NLRIs do not contain
an RD of the VRF from which they are exported: the C-multicast Join
routes and the Leaf A-D routes.
Those route types that, when exported from a given VRF, contain (in
their NLRIs) an RD of the VRF, will be known in this document as
"local-RD routes".
Given the "unique VRF per RD condition", if one sees that two local-
RD routes have the same RD, one can infer that the two routes
originated from the same VRF. This inference can be drawn even if
the two routes do not have the same SAFI, as long as the two routes
are both local-RD routes.
This document builds upon [MVPN] and [MVPN-BGP], and therefore
REQUIREs the "unique VRF per RD" condition.
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[MVPN-BGP] presupposes a further requirement on the use of RDs in the
local-RD routes exported from a given VRF. Suppose a given VRF
exports a Source Active A-D route containing (C-S,C-G). That VRF
will also export a UMH-eligible route matching C-S. [MVPN-BGP]
presupposes that the UMH-eligible route and the Source Active A-D
route have the same RD.
In most cases, not only is a given RD associated with a single VRF,
but a given VRF is associated with a single RD. We will call this
the "unique RD per VRF" condition. When this condition holds, all
the local-RD routes exported from a given VRF will have the same RD.
This ensures that the presupposition of the previous paragraph will
hold, i.e., that the RD in a Source Active A-D route exported from a
given VRF will have the same RD as the corresponding UMH-eligible
route exported from the same VRF.
Section 7.3 of this document describes a procedure known as "Extranet
Separation". When Extranet Separation is NOT being used, this
document REQUIREs that the "unique RD per VRF" condition hold. This
ensures that all the local-RD routes exported from a given VRF will
have the same RD.
When Extranet Separation is used, a VRF that contains both extranet
sources and non-extranet sources MUST be configured with two RDs: the
"default RD" (discussed above) and the "extranet RD". The "unique
VRF per RD" condition also applies to the "extranet RD", i.e., a
given extranet RD is associated with a unique VRF. Details
concerning the exported routes that contain the extranet RD can be
found in sections 4.1 and 7.3.
1.4. Overview
Consider two VPNs, VPN-S and VPN-R, each of which supports MVPN
functionality as specified in [MVPN] and/or [MVPN-BGP]. In the
simplest configuration, VPN-S is a collection of VRFs, each of which
is configured with a particular Route Target (RT) value (call it
"RT-S") as its import RT and as its export RT. Similarly, VPN-R is a
collection of VRFs, each of which is configured with a particular RT
value (call it "RT-R") as its import RT and as its export RT.
In this configuration, multicast C-receivers contained in a VPN-R VRF
cannot receive multicast data traffic from multicast C-sources
contained in a VPN-S VRF. If it is desired to allow this, one needs
to create an MVPN "extranet". Creating an extranet requires
procedures in addition to those specified in [MVPN], [MVPN-BGP], and
[MVPN-WILDCARDS]; this document specifies these additional
procedures.
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In the example above, the additional procedures will allow a selected
set of routes exported from the VPN-S VRFs (i.e., from the VRFs
containing extranet C-sources) to be imported into the VPN-R VRFs
(i.e., into the VRFs containing extranet C-receivers). These routes
include the routes that are to be eligible for use as UMH routes (see
Section 5.1 of [MVPN]) in the extranet, as well as a selected set of
BGP A-D routes (Intra-AS I-PMSI A-D routes, S-PMSI A-D routes, Source
Active A-D routes). Importing these routes into the VPN-R VRFs makes
it possible to determine, in the context of a VPN-R VRF, that a
particular C-multicast Join needs to be delivered to a particular
VPN-S VRF. It also makes it possible to determine, in the context of
a VPN-R VRF, the P-tunnel through which the aforementioned VPN-S VRF
sends a particular C-flow.
Depending on the type of P-tunnel used, it may also be necessary for
Leaf A-D routes to be exported by one or more VPN-R VRFs and imported
into a VPN-S VRF.
There are no extranet-specific procedures governing the use and
distribution of BGP C-Multicast routes.
If PIM is used as the PE-PE protocol for distributing C-multicast
routing information, additional BGP A-D routes must be exported from
the VPN-R VRFs and imported into the VPN-S VRFS, so that the VPN-S
VRFs can join the P-tunnels that the VPN-R VRFs use for sending PIM
control messages. Details can be found in Section 6.
The simple example above describes an extranet created from two
MVPNs, one of which contains extranet C-sources and one of which
contains extranet C-receivers. However, the procedures described in
this document allow for much more complicated scenarios.
For instance, an extranet may contain extranet C-sources and/or
extranet C-receivers from an arbitrary number of VPNs, not just from
two VPNs. An extranet C-receiver in VPN-R may be allowed to receive
multicast traffic from extranet C-sources in VPN-A, VPN-B, and VPN-C.
Similarly, extranet C-sources in VPN-S may be allowed to send
multicast traffic to multicast C-receivers that are in VPN-A, VPN-B,
VPN-C, etc.
A given VPN customer may desire that only some of its multicast
C-sources be treated as extranet C-sources. This can be accomplished
by appropriate provisioning of the import and export RTs of that
customer's VRFs (as well as the VRFs of other VPNs that contain
extranet C-receivers for extranet C-flows of the given customer.)
A given VPN customer may desire that some of its extranet C-sources
can transmit only to a certain set of VPNs, while other of its
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extranet C-sources can transmit only to a different set of VPNs. This
can be accomplished by provisioning the VRFs to export different
routes with different RTs.
In all these cases, the VPN customers set the policies, and the
Service Provider (SP) implements the policies by the way it
provisions the import and export RTs of the VRFs. It is assumed that
the customer communicates to the SP the set of extranet C-source
addresses, and the set of VPNs to which each C-source can transmit.
(Recall that every C-source that can transmit to an extranet C-group
is an extranet C-source, and must be able transmit to any VPN that
has receivers for that group. This must be taken into account when
the provisioning is done.) This customer/SP communication is part of
the service provisioning process, and outside the scope of this
document.
It is possible that an extranet C-source will transmit both extranet
C-flows and non-extranet C-flows. However, if extranet C-receiver
C-R can receive extranet C-flows from extranet C-source C-S, the
procedures of this document do not prevent C-R from requesting and
receiving the non-extranet flows that are transmitted by C-S.
Therefore it is NOT RECOMMENDED to allow an extranet C-source to
transmit non-extranet C-flows. However, the Service Provider (SP)
has no control over the set of C-flows transmitted by a given
C-source, and can do no more than communicate this recommendation to
its customers. (Alternatively, the customer and SP may coordinate on
setting up filters to prevent unauthorized flows from being sent to a
customer site; such a procedure is outside the scope of this
document.) See the "Security Considerations" section for additional
discussion of this issue.
2. Extranets and Overlapping Address Spaces
As specified in [L3VPN], the address space of one VPN may overlap
with the address space of another. A given address may be
"ambiguous", in that it denotes one system within VPN-A and a
different system within VPN-B. In the notation of section 1.1, if an
address C-S is ambiguous between VPNs A and B, then Host(C-S,A) !=
Host(C-S,B). However, any given address C-S must be unambiguous
(i.e., denotes a single system) in the context of a given VPN.
When a set of VRFs belonging to different VPNs are combined into an
extranet, it is no longer sufficient for an address to be unambiguous
only within the context of a single VPN:
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1. Suppose C-S is the address of a given extranet C-source
contained in VPN-A. Now consider the set of VPNs {VPN-B, VPN-
C, ...} containing extranet C-receivers that are allowed by
policy to receive extranet C-flows from VPN-A's C-S. The
address C-S MUST be unambiguous among this entire set of VPNs
(VPN-A, VPN-B, VPN-C, etc.); i.e., Host(C-S,A) == Host(C-S,B)
== Host(C-S,C).
The implication is that C-S in VPN-A is not necessarily an
extranet C-source for all VPNs that contain extranet C-
receivers; policy MUST be used to ensure that C-S is an
extranet C-source for a given VPN, say VPN-B, only if C-S is
unambiguous between VPN-A and VPN-B.
2. If a given VRF contains extranet C-receivers for a given
extranet C-source, then the address of this C-source MUST be
unambiguous among all the extranet C-sources for which there
are C-receivers in the VRF. This is true whether or not
C-sources are in VRFs that belong to the same or to different
VPNs.
The implication is that if C-S in VRF-X is ambiguous with C-S
in VRF-Y, then there MUST NOT be any VRF, say VRF-Z, containing
C-receivers that are allowed by policy to receive extranet C-
flows from both C-S in VRF-X and C-S in VRF-Y.
Note: A VPN customer may be using "anycast" addresses. An anycast
address is intentionally ambiguous, as it denotes a set of systems
rather than a single system. In this document, we will consider an
anycast address to be unambiguous in a given context as long as it
denotes the same set of systems whenever it occurs in that context.
A multicast C-group address, say C-G, may also be ambiguous, in that
it may be used for one multicast group in VPN-A and for an entirely
different multicast group in VPN-B. If a set of MVPNs are combined
into an extranet, and C-G is an extranet C-group, it is necessary to
ensure that C-G is unambiguous among the entire set of VPNs whose
VRFs contain extranet C-sources, C-RPs, and/or extranet C-receivers
for that C-group. This may require, as part of the provisioning
process, customer/SP communication that is outside the scope of this
document.
Subject to these restrictions, the SP has complete control over the
distribution of routes in an MVPN. This control is exerted either by
provisioning the export RTs on the VRFs that originate the routes
(i.e., on the VRFs that contain the extranet C-sources), or by
provisioning the the import RTs on the VRFs that receive the routes
(i.e., on the VRFs that contain the extranet C-receivers), or both.
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Some of the rules and restrictions on provisioning the RTs are
applicable to all extranets; these are specified in Section 4.
Sections 6 and 7 add additional rules and restrictions that are
applicable only to particular extranet scenarios.
Even if all the RTs are provisioned according according to the above
rules and restrictions, it is still possible for a single P-tunnel to
contain multicast data packets whose source and/or group addresses
are ambiguous in the context of the set of PEs that receive data from
the P-tunnel. That is, the above rules and restrictions are
necessary, but not sufficient, to prevent address ambiguity from
causing misdelivery of traffic. To prevent such misdelivery,
additional procedures or policies must be used.
Sections 2.1 and 2.2 describe scenarios in which a given P-tunnel may
carry data packets with ambiguous addresses. The additional
procedures and policies needed to prevent misdelivery of data in
those scenarios are outlined in those section 2.3. (The detailed
procedures described in Sections 6 and 7 incorporate the
considerations of Section 2.3.)
2.1. Ambiguity: P-tunnel with Extranet/Non-Extranet Flows
In the following, we will use the notation "VRF A-n" to mean "VRF n
of VPN-A".
If VPN-A and VPN-B have overlapping address spaces, and are part of
the same extranet, then the following problem may exist, as
illustrated in Figure 1.
C-S2(A) C-S1 Join(C-S2(A),G)
\ / /
\ / /
+-------+---+ P1: (C-S1,G), (C-S2(A),G) +---+--------+
|VRF A-1| |---------------------------------| |VRF A-2 |
+-------+PE1| |PE2+--------+
|VRF B-1| |---------------------------------| |VRF B-2 |
+-------+---+ P2: (C-S2(B),G) +---+--------+
/ / \
/ / \
C-S2(B) Join(C-S2(B),G) Join(C-S1,G)
Figure 1 Ambiguity of Extranet and Non-Extranet Source Address
Suppose:
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- C-G is an SSM C-group used in VPNs A and B.
- VRF A-1, on PE1, contains an extranet C-source, whose IP address
is C-S1, that is allowed to have receivers in VPN B. VRF A-1
thus exports to VPN B a UMH-eligible route matching C-S1.
- VRF A-1 also contains a non-extranet C-source, whose IP address
is C-S2. VRF A-1 exports a UMH-eligible route matching C-S2 to
other VPN A VRFs, but NOT to VPN B.
- VRF B-1, also on PE1, contains a non-extranet C-source whose IP
address is C-S2. A UMH-eligible route matching C-S2 is thus
exported from VRF B-1 to other VRFs in VPN B.
- Host(C-S2,A) != Host(C-S2,B). That is, C-S2 is an ambiguous
address in any extranet that contains both VPN-A VRFs and VPN-B
VRFs.
- VRF B-2, on some other PE, say PE2, requests to receive the
multicast flow (C-S1,C-G). In the context of VRF B-2, C-S1
matches the route exported from VRF A-1. Thus B-2's request to
receive the (C-S1,C-G) flow is transmitted to VRF A-1.
- VRF A-1 responds to VRF B-2's request for (C-S1,C-G) traffic by
transmitting that traffic on P-tunnel P1.
- VRF B-2 joins P-tunnel P1, in order to receiver the (C-S1,C-G)
traffic.
- VRF A-2, on PE2, requests to receive the (non-extranet) multicast
flow (C-S2,C-G). In the context of VRF A-2, C-S2 matches the
route exported from VRF A-1. Thus A-2's request to receive the
(C-S2,C-G) traffic is transmitted to VRF A-1.
- VRF A-1 responds to VRF A-2's request for (C-S2,C-G) traffic by
transmitting that traffic on P-tunnel P1.
- VRF A-2 joins P-tunnel P1, in order to receive the (C-S2,C-G)
traffic.
- VRF B-2 requests to receive the (non-extranet) multicast flow
(C-S2,C-G). In the context of VRF B-2, C-S2 matches the route
exported from VRF B-1. Thus B-2's request to receive the
(C-S2,C-G) flow is transmitted to VRF B-1.
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- VRF B-1 responds to VRF B-2's request for (C-S2,C-G) traffic by
transmitting that traffic on P-tunnel P2.
- VRF B-2 joins P-tunnel P2.
Since VRF B-2 has joined P-tunnel P1 and P-tunnel P2, it will receive
(C-S2,C-G) traffic on both P-tunnels. The (C-S2,C-G) traffic that
VRF B-2 needs to receive is traveling on P-tunnel P2; this (C-S2,C-G)
traffic must be forwarded by B-2 to any attached customer sites that
have C-receivers for it. But B-2 MUST discard the (C-S2,C-G) traffic
that it receives on P1, as this is not the traffic that it has
requested. If the (C-S2,C-G) traffic arriving on P1 were forwarded
to B-2's customer sites, the C-receivers would not be able to
distinguish the two flows, and the result would be a corrupted data
stream.
Note that the procedures of [MVPN] Section 9.1.1 ("Discarding Packets
from the Wrong PE") will not cause VRF B-2 to discard the (C-S2,C-G)
that arrives on tunnel P1, because P1 and P2 have the same upstream
PE.
Therefore, it is necessary EITHER to prevent the above scenario from
occurring, OR ELSE to ensure that multicast data packets will be
discarded if they arrive on the "wrong" P-tunnel (even if they arrive
from the expected PE). See Section 2.3 for further discussion of
this issue.
2.2. Ambiguity: P-tunnel with Multiple Extranet Flows
Here is another example in which overlapping address spaces may cause
a problem. This example is illustrated in Figure 2.
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C-S2(A2D) C-S1(A2C) Join(C-S2(A2D),G)
\ / /
\ / /
+-------+---+ P1: (C-S1(A2C),G), (C-S2(A2D),G)+---+--------+
|VRF A-1| |---------------------------------| |VRF D-1 |
+-------+PE1| |PE2+--------+
|VRF B-1| |---------------------------------| |VRF C-1 |
+-------+---+ P2: (C-S2(B2C),G) +---+--------+
/ / \
/ / \
C-S2(B2C) / \
Join Join
(C-S2(B2C),G) (C-S1(A2C),G)
Figure 2 Ambiguity of Extranet Source Addresses
Suppose:
- C-G is an SSM C-group address that is used in VPNs A, B, C, and
D.
- VRF A-1, on PE1, contains an extranet C-source whose IP address
is C-S1, and that is allowed by policy to have C-receivers in VPN
C (but not in VPN D). VRF A-1 thus exports a UMH-eligible route
matching C-S1 to VPN C.
- VRF A-1 also contains an extranet C-source whose IP address is
C-S2, and that is allowed by policy to have C-receivers in VPN D
(but not in VPN C). VRF A-1 thus exports a UMH-eligible route
matching C-S2 to VPN D.
- VRF B-1, also on PE1, contains an extranet C-source whose IP
address is C-S2, and that is allowed by policy to have
C-receivers in VPN C (but not in VPN D). VRF B-1 thus exports a
UMH-eligible route matching C-S2 to VPN C.
- Host(C-S2,A) != Host (C-S2,B). That is, C-S2 is an ambiguous
address in any extranet that contains both VPN-A VRFs and VPN-B
VRFs.
- VRF C-1, on some other PE, say PE2, requests to receive the
extranet multicast flow (C-S1,C-G). In the context of VRF C-1,
C-S1 matches the route exported from VRF A-1. Thus C-1's request
to receive the (C-S1,C-G) flow is transmitted to VRF A-1.
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+ VRF A-1 responds to VRF C-1's request for (C-S1,C-G) traffic by
transmitting that traffic on P-tunnel P1,
- VRF C-1 joins P-tunnel P1, in order to receive the (C-S1,C-G)
traffic.
- VRF C-1 requests to receive the extranet multicast flow
(C-S2,C-G). In the context of VRF C-1, C-S2 matches the route
exported from VRF B-1. Thus C-1's request to receive the
(C-S2,C-G) flow is transmitted to VRF B-1.
- VRF B-1 responds by transmitting its (C-S2,C-G) traffic on
P-tunnel P2.
- VRF C-1 joins P-tunnel P2 in order to receive the (C-S2,C-G)
traffic.
- VRF D-1, on PE2, requests to receive the extranet multicast flow
(C-S2,C-G). In the context of VRF D-1, C-S2 matches the route
exported from VRF A-1. Thus D-1's request to receive the
(C-S2,C-G) flow is transmitted to VRF A-1.
- VRF A-1 responds by transmitting its (C-S2,C-G) traffic on
P-tunnel P1.
- VRF D-1 joins P-tunnel P1 in order to receive the (C-S2,C-G)
traffic.
In this example, VRF A-1 has chosen to use the same P-tunnel, P1, to
carry both its (C-S2,C-G) traffic and the (C-S1,C-G) traffic. VRF
C-1 has joined tunnel P1 in order to receive the (C-S1,C-G) traffic
from VRF A-1, which means that VRF C-1 will also receive the unwanted
(C-S2,C-G) traffic from P1. VRF C-1 is also expecting (C-S2,C-G)
traffic from VRF B-1; this traffic will be received from P2. Thus
VRF C-1 is receiving (C-S2,C-G) traffic on both tunnels, and both
C-flows arrive from the expected PE, PE1.
Therefore, it is necessary EITHER to prevent the above scenario from
occurring, OR ELSE to ensure that VRF C-1 discards any (C-S,C-G)
traffic that arrives from the "wrong" P-tunnel. See Section 2.3 for
further discussion of this issue.
Note that the ambiguity described in this Section (2.2) would not
occur if C-G were an (ASM) extranet C-group. In that case, the
scenario would violate the rule, given previously in Section 2,
requiring that all sources sending to a particular ASM extranet
C-group must have addresses that are unambiguous over all the MVPNs
receiving traffic for that C-group.
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2.3. Preventing Misdelivery in These Scenarios
There are two ways to prevent the scenarios of Sections 2.1 and 2.2
from resulting in misdelivery of data. These two ways are discussed
respectively in Sections 2.3.1 and 2.3.2.
2.3.1. Do Not Deliver Packets from the 'Wrong' P-tunnel
Consider a particular C-flow that has receivers in a particular VRF.
Sections 6 and 7 describe a set of procedures that enable an egress
PE to determine the "expected P-tunnel" for that C-flow in the
context of that VRF. If a PE receives packets of the C-flow (as
determined by the IP source and/or destination address of the
packet), it checks to see if the packet was received on the expected
P-tunnel for that VRF. If so, the packet is delivered to the VRF
(and thus to the C-flow's receivers in that VRF). If not, the packet
is not delivered to the VRF.
Note that at a given egress PE, the "wrong" P-tunnel for one VRF may
be the right P-tunnel for another.
These procedures, if applied at every PE that joins a given P-tunnel,
are sufficient to prevent misdelivery of traffic in the scenarios of
Sections 2.1 and 2.2.
IF these procedures cannot be applied by every PE that is attached to
a given extranet, then the policies of Section 2.3.2 MUST be applied
at every VRF containing C-sources for that extranet.
In some cases, however, it may be safe to deliver packets that arrive
from other than the expected P-tunnel. Suppose it is known that
every packet gets transmitted on only a single P-tunnel. (This will
be the case if the "single PMSI per C-flow" transmission model,
discussed in section 3.1, is being used.) Suppose further that it is
known that T1 and T2 carry only packets that arrived at the same
ingress PE, over one or more VRF interfaces that are associated with
the same VRF. (I.e., that there is a particular VRF that is the
ingress VRF for ALL the packets carried by T1 or T2.) In this case,
if T1 is the expected P-tunnel for a given (C-S,C-G) , it is NOT
necessary to discard (S,G) packets that arrive over T2.
It is not always possible to determine whether two P-tunnels are
carrying packets from the same ingress VRF. However, in some cases,
this can be determined by examination of the A-D routes in which the
tunnels have been advertised.
Consider the following example:
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- Tunnel T1 is a P2MP mLDP or RSVP-TE P-tunnel advertised in an
Intra-AS I-PMSI A-D route, call it R1.
- Tunnel T2 is a P2MP mLDP or RSVP-TE P-tunnel advertised in an S-
PMSI A-D route, call it R2.
- The respective NLRIs of R1 and R2 contain the same RD value.
- The MPLS Label field of R1's PMSI Tunnel attribute is zero, and
the MPLS label value of R2's PMSI Tunnel attribute is zero.
In this example, it can be concluded that T1 and T2 are carrying
packets from the same ingress VRF. Thus if T1 is the expected
P-tunnel for a (C-S,C-G) flow, (S,G) packets from T2 can be safely
delivered to the egress VRF; they do not need to be discarded.
Similarly, if T2 is the expected P-tunnel for a (C-S,C-G) flow, (S,G)
packets from T1 can be safely delivered to the egress VRF.
Another example is the following:
- Tunnel T3 is a P2MP mLDP or RSVP-TE P-tunnel advertised in a
(C-*,C-*) S-PMSI A-D route, call it R3.
- Tunnel T4 is a P2MP mLDP or RSVP-TE P-tunnel advertised in a (C-
S,C-G) S-PMSI A-D route, call it R4.
- The respective NLRIs of R3 and R4 contain the same RD value.
- The MPLS Label field of R3's PMSI Tunnel attribute is zero, and
the MPLS label value of R4's PMSI Tunnel attribute is zero.
In this example, it can be concluded that T3 and T4 are carrying
packets from the same ingress VRF. Thus if T3 is the expected
P-tunnel for a (C-S,C-G) flow, (S,G) packets from T4 can be safely
delivered to the egress VRF; they do not need to be discarded.
Similarly, if T4 is the expected P-tunnel for a (C-S,C-G) flow, (S,G)
packets from T3 can be safely delivered to the egress VRF.
When Ingress Replication P-tunnels are being used, please see [MVPN-
IR], especially section 6 ("The PTA's MPLS Label Field") for a
discussion of how to determine when packets from other than the
expected P-tunnel must be discarded.
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2.3.2. Policies to Prevent Ambiguity on a P-tunnel
For P-tunnels that are advertised in S-PMSI A-D routes whose NLRI
contains (C-S,C-G) or (C-S,C-*), the ambiguities described in
Sections 2.1 and 2.2 can be prevented by provisioning a policy that
assigns, to such P-tunnels, only flows from the same C-source.
However, it is not always possible to determine, through inspection
of the control messages, whether this policy has been deployed. For
instance, suppose a given VRF has imported a set of S-PMSI A-D
routes, that each route in the set has bound only a single
(C-S1,C-G1) to a single P-tunnel, and that each route in the set
identifies a different P-tunnel in its PTA than is identified by the
PTA of any other route in the set. One cannot infer from this that
there is no ambiguity, as the same P-tunnel may also have been
advertised in an S-PMSI A-D route that is not imported by the given
VRF, and that S-PMSI A-D route may have bound (C-S2,C-G2) to the
P-tunnel, where C-S1 != C-S2.
Therefore, in order to determine that a given P-tunnel (advertised in
a (C-S,C-G) or (C-S,C-*) S-PMSI A-D route) carries only C-flows from
a single C-source, a PE must have a priori knowledge (through
provisioning) that this policy has been deployed. In the remainder
of this document, we will refer to this policy as the "Single
C-source per (C-S,C-G) or (C-S,C-*) P-tunnel" policy. Note that this
policy is only applicable to P-tunnels that are advertised only in
(C-S,C-G) or (C-S,C-*) S-PMSI A-D routes.
Of course, if a P-tunnel is advertised in (a) an I-PMSI A-D route, or
(b) an S-PMSI A-D route whose NLRI contains (C-*,C-*), or (c) an
S-PMSI A-D route whose NLRI contains (C-*,C-G), then it is always
possible for the P-tunnel to contain traffic from multiple C-sources;
there is no policy that can prevent that.
However, if a P-tunnel advertised in a (C-*,C-G) S-PMSI A-D route
contains only traffic addressed to a single C-G, the address
uniqueness rules of section 2 prevent the C-source addresses from
being ambiguous; the set of C-sources transmitting to a particular
extranet C-group address must be unambiguous over the set of MVPNs
that have receivers for that C-group. So for P-tunnels that are
advertised in (C-*,C-G) S-PMSI A-D routes, the ambiguities described
Sections 2.1 and 2.2 can be prevented by provisioning a policy that
assigns, to such P-tunnels, only flows to the same extranet C-group.
We will refer to this policy as the "Single C-group per (C-*,C-G)
P-tunnel" policy.
These considerations can be summarized as follows. IF the procedures
referenced in Section 2.3.1 cannot be applied, then the PEs MUST be
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provisioned so that the all of the following conditions hold true of
the VRFs that contain extranet C-sources:
- the "Single C-source per (C-S,C-G) or (C-S,C-*) P-tunnel" policy
is provisioned, and
- either no (C-*,C-G) S-PMSI A-D routes are advertised, or else the
"Single C-group per (C-*,C-G) P-tunnel" policy is provisioned,
and
- no P-tunnels are advertised in I-PMSI A-D routes, and
- no (C-*,C-*) S-PMSI A-D routes are advertised.
Section 3 of this document describes a procedure known as "extranet
separation". When extranet separation is used, the ambiguity of
section 2.1 is prevented. However, the ambiguity of section 2.2 is
not prevented by extranet separation. Therefore, the use of extranet
separation is not a sufficient condition for avoiding the procedures
referenced in section 2.3.1. Extranet separation is, however, implied
by the policies discussed in this section (2.3.2).
3. Extranet Transmission Models
This document specifies several "extranet transmission models". A
given VRF, containing extranet C-sources or C-receivers, MUST use
only one of these models. Further if VRF S contains extranet
C-sources, VRF R contains extranet C-receivers, and it is allowed by
policy for an extranet C-receiver in VRF R to receive a C-flow from
an extranet C-source in VRF S, then VRFs S and R MUST use the same
extranet transmission model. The model used by a given VRF is
determined by provisioning.
3.1. Transmitting an Extranet C-flow on a Single PMSI
In one extranet transmission model, which we call the "transmitting
an extranet C-flow on a single PMSI" model, or more simply, the
"single PMSI per C-flow model", a PE transmitting a packet of an
extranet C-flow transmits it on only a single PMSI. If the PMSI is
instantiated by a multicast P-tunnel, this means that the PE
transmits the packet on a single P-tunnel. Of course, if the PE is a
replication point for that multicast P-tunnel, the packet is
transmitted more than once by the PE. Similarly, if the PMSI is
instantiated by a set of unicast tunnels (i.e., via Ingress
Replication), each packet may be transmitted multiple times. It is
still the case though that the packet is transmitted only on one
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PMSI.
This document provides procedures for supporting this transmission
model using either BGP or PIM as the PE-PE C-multicast control
protocol.
There are two variants of this transmission model: "without extranet
separation" and "with extranet separation".
3.1.1. Without Extranet Separation
In this variant, multicast data traffic from extranet C-sources and
from non-extranet C-sources may be carried in the same P-tunnel.
This document provides procedures for supporting this variant using
either BGP or PIM as the PE-PE C-multicast control protocol.
3.1.2. With Extranet Separation
In this variant, multicast data traffic from extranet C-sources and
from non-extranet C-sources are never carried in the same P-tunnel.
Under certain circumstances, this can reduce the amount of multicast
data traffic that is delivered unnecessarily to certain PE routers.
It also eliminates the ambiguity discussed in Section 2.1.
By definition, when extranet separation is used, the following rule
MUST be applied:
Traffic from extranet C-sources MUST NOT be carried in the same
P-tunnel as traffic from non-extranet C-sources.
This rule does not impact those VRFs that contain only non-extranet
C-sources, nor does it impact those VRFs that contain only extranet
C-sources. However, if a particular VRF contains both kinds of
C-source, it will need to advertise some P-tunnels that are used for
carrying only extranet C-flows, and some that are used only for
carrying non-extranet C-flows.
This document provides procedures for supporting extranet separation
when BGP is used as the PE-PE C-multicast control protocol. Support
for extranet separation using PIM as the PE-PE C-multicast control
protocol is outside the scope of this document.
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3.2. Transmitting an Extranet C-flow over Multiple PMSIs
The second extranet transmission model is called the "transmitting an
extranet C-flow over multiple PMSIs" model, or more simply, the
"multiple PMSIs per C-flow model". In this model, a PE may transmit
the packets of an extranet C-flow on several different PMSIs.
Support for extranet separation with this model is outside the scope
of this document.
This document provides procedures for supporting this transmission
model when PIM as the PE-PE C-multicast control protocol. Support for
this transmission model when BGP is used as the PE-PE C-multicast
control protocol is outside the scope of this document.
4. Distribution of Routes that Match C-S/C-RP Addresses
4.1. UMH-Eligible Routes
As described in Section 5.1 of [MVPN], in order for a C-flow
(C-S,C-G) to be carried across the SP backbone, a VRF that has
multicast receivers for that C-flow MUST import a route that matches
C-S, and this route must be "eligible for UMH selection". In this
document, we will refer to these routes as "UMH-eligible extranet
C-source routes".
The UMH-eligible extranet C-source routes do not necessarily have to
be unicast routes. If one wants, e.g., a VPN-R C-receiver to be able
to receive extranet C-flows from C-sources in VPN-S, but one does not
want any VPN-R system to be able to send unicast traffic to those
C-sources, then the UMH-eligible routes exported from VPN-S and
imported by VPN-R MAY be SAFI-129 routes (see Section 5.1.1 of
[MVPN]). The SAFI-129 routes are used only for UMH determination,
but not for unicast routing.
If a customer is using PIM-SM in ASM mode, and one or more customer
sites have C-receivers that are allowed by policy to join a (C-*,C-G)
tree, where C-G is an extranet C-group, then any VRF with C-receivers
for that group MUST import a UMH-eligible route that matches C-RP,
where C-RP is the Rendezvous Point (RP) address for C-G.
The UMH-eligible extranet C-source and C-RP routes do not have to be
"host routes." That is, they can be routes whose IPv4 address
prefixes are not 32 bits in length, or whose IPv6 address prefixes
are not 128 bits in length. So it is possible for a UMH-eligible
extranet C-source route to match the address of an extranet C-source
and to also match the address of a non-extranet C-source. However,
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if such a route is exported from a VPN-S VRF and imported by a VPN-R
VRF, VPN-R receivers will be able to receive C-flows from any non-
extranet C-sources whose addresses match that route. To prevent
this, the VPN-S VRF SHOULD be provisioned such that it will NOT
export a UMH-eligible route that matches (in the context of the VPN-R
VRF) both extranet C-sources and non-extranet C-sources. Failure to
follow this rule may result in a VPN security violation. (See Section
10.)
In general, one does not want ALL the routes from the VPN-S VRFs to
be exported to all the VPN-R VRFs, as only a subset of the routes in
the VPN-S VRFs will be UMH-eligible extranet C-source routes. Route
distribution is, as always in a BGP/MPLS IP VPN [L3VPN], controlled
by Route Targets (RTs). A variety of route distribution policies can
be created by appropriately provisioning the import and export RTs of
the various VRFs.
For example, the VPN-S VRFs that contain extranet C-sources could be
configured to apply an export RT whose value is "RT-A-extranet" to
the routes that match the extranet C-sources. The VPN-R VRFs that
contain extranet C-receivers allowed to receive extranet C-flows from
VPN-S extranet C-sources could then be configured with
"RT-A-extranet" as an import RT.
Arbitrarily complex policies can be created by suitable manipulation
of the import and export RTs.
4.1.1. Extranet Separation
If Extranet Separation is being used, and if a given VRF is exporting
UMH-eligible routes both for extranet C-sources for non-extranet
C-sources, then the VRF MUST be configured not only with its "default
RD", but also with an "extranet RD". The exported UMH-eligible
routes MUST contain the extranet RD in their NLRIs.
4.2. Distribution of Unicast Routes Matching C-RPs and DRs
Consider a C-source, C-S, that may transmit to a particular extranet
C-group, C-G.
In order to follow the procedures of [PIM],
- the "first hop designated router" (DR) of C-S needs to be able to
unicast "PIM Register Messages" to a C-RP that services C-G;
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- the C-RPs servicing C-G need to be able to unicast "PIM Register-
Stop Messages" to the DR of C-S.
It follows that if a VRF contains C-S, but does not contain a C-RP
for C-G, then the VRF must import a unicast route matching a C-RP for
C-G. Note that the unicast route matching the C-RP is needed whether
or not the VRF has also imported a SAFI-129 route matching the C-RP.
(If the VRF also contains receivers for C-G, and if UMH determination
is being done using SAFI-129 routes, both a unicast route and a
SAFI-129 matching C-RP route are needed.)
Similarly, if a VRF contains a C-RP for C-G, but does not contain
C-S, the VRF must import a unicast route matching the DR for C-S.
Note that the unicast route matching the DR for C-S is needed even if
UMH determination is being done using SAFI-129 routes; in that case,
if the VRF also contains receivers for C-G, it needs to import a
SAFI-129 route matching C-S and a unicast route matching the DR for
C-S.
If, for a particular extranet C-group, C-G, the customer is using
"anycast-RP"([RFC3446], [RFC4610]) or MSDP [RFC3618], then all the
C-RPs serving C-G need to send unicast messages to each other. Thus
any VRF that contains a C-RP for C-G needs to import unicast routes
matching ALL the other C-RPs that serve C-G.
The need to distribute these unicast routes is usually not a problem
as long as all the C-sources and C-RPs for C-G are in the same MVPN.
If, however, the C-sources are not all in the same MVPN, great care
must be taken to ensure that the unicast routes mentioned above are
properly distributed.
There may be scenarios in which all the C-sources for C-G are in the
same MVPN, but there are receivers in different VPNs, and some or all
of the VPNs with receivers have their own C-RPs for C-G. In this
case, care must be taken to ensure that the C-RPs can all unicast to
each other.
4.3. Route Targets and Ambiguous UMH-Eligible Routes
This section imposes constraints on the way RTs are assigned to (a)
UMH-eligible routes and to (b) the BGP A-D routes that advertise
P-tunnels (i.e., to BGP A-D routes that contain a PTA). The
constraints specified here apply to any extranet for which the
ambiguity of Section 2.2 is possible. (The conditions under which
such ambiguity is possible are described in Section 2.2.)
We want to ensure that, in any given VRF, the UMH-eligible route
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matching a given extranet C-source has an RT in common with every BGP
A-D route that advertises a P-tunnel that may be used to carry
extranet multicast traffic from that C-source. We also want to
ensure that the UMH-eligible route matching a given extranet C-source
does not have any RT in common with any BGP A-D route that advertises
a P-tunnel that may be used to carry any multicast traffic from a
different C-source that has the same IP address. This enables us to
determine whether traffic that appears to be from the given C-source
is really arriving on the "wrong tunnel", and hence is really from a
different C-source with the same IP address.
Suppose an IP address C-S is used in VPN-A as the address of one
system, and is used in VPN-B as the address of a different system.
In this case, one or more VPN-A VRFs may export a VPN-IP route whose
NLRI is <RD1,S>, and one or more VPN-B VRFs may export a VPN-IP route
whose NLRI is <RD2,S>, where RD1 != RD2. Consider two routes, R1 and
R2, for which the following conditions all hold:
- R1 and R2 are UMH-eligible extranet C-source or C-RP routes, or
are unicast routes matching a C-RP
- R1 is exported from a VRF of VPN-A, while R2 is exported from a
VRF of a different VPN, say VPN-B
- R1's NLRI specifies IP address prefix S/n
- R2's NLRI specifies IP address prefix S/m
- m >= n, (S/m is either the same as or more specific than S/n)
- There is some host address H such that:
* H denotes a different system in VPN-A than in VPN-B,
* H/m == S/m (so either S/m or S/n might be a longest match for
H in some VRF).
We impose the following constraint: RTs MUST be assigned in such a
way that R1 and R2 do not have any RT in common.
(This constraint is not as onerous at it may seem. Typically R1 and
R2 would not have an RT in common, as that might result in their
being imported into the same VRF, making the address H ambiguous in
that VRF.)
Sections 6 and 7 specify procedures for determining if a received
C-flow has been received over the expected P-tunnel. Those
procedures will not work if this constraint is violated. (The
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constraint described in this section is necessary but not sufficient
for the procedures of those sections to work; additional constraints,
covering the assignment of RTs to BGP A-D routes, are given in
subsequent sections.)
4.4. Dynamically Marking Extranet Routes
4.4.1. The Extranet Source Extended Community
Sections 4.1-4.3 place specific requirements on the way in which
certain VPN-IP routes are distributed. In order to ensure that these
requirements are met, a VPN customer must tell its SP which routes
are the matching routes for extranet C-sources and C-RPs. This may
be done as part of the provisioning process. Note that this does not
necessarily require customer/provider interaction every time the
customer adds a new extranet C-source or C-RP, but only when the IP
address of the new C-source or C-RP does not match an existing route
that is already being distributed as a VPN-IP extranet route.
Nevertheless, it seems worthwhile to support an OPTIONAL mechanism
that allows a customer to dynamically mark certain routes as being
extranet routes.
To facilitate this, we define a new transitive opaque extended
community, the "Extranet Source" extended community. When a CE
router advertises (via BGP) a route to a PE router, and the AFI/SAFI
of the route is 1/1, 1/2, 1/4, 2/1, 2/2, or 2/4, the Extranet Source
extended community MAY be attached to the route. The value field of
the extended community MUST be set to zero. By placing this extended
community on a particular route, a CE router indicates to a PE router
that the procedures of sections 4.1-4.3 are to be applied to that
route. That is, the CE router may use this extended community to
indicate to the PE router that a particular route is to be treated as
a route that matches the address of an extranet source, and exported
accordingly to other VPNs.
Whether a CE router uses the Extranet Source extended community is
determined by the configuration of the CE router. If used, the set
of routes to which the extended community is attached is also
determined by configuration of the CE. Note that a particular PE
router may or may not support the use of the Extranet Source extended
community by a particular CE router; this is determined by the
service agreement between the SP and its customer.
If a CE is advertising SAFI-2 routes to the PE as the UMH-eligible
extranet C-source and C-RP routes, and if the CE is using the
Extranet Source extended community, it is important that the CE
attach that extended community to the SAFI-2 routes, rather than just
to the corresponding SAFI-1 routes. Otherwise extranet receivers may
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not be able to join the (C-S,C-G) or (C-*,C-G) multicast trees.
However, if the C-sources and the C-RPs for a given extranet C-group
are not all in the same VPN, the extended community would also have
to be attached to the SAFI-1 routes that match the C-RP addresses and
to the SAFI-1 routes that match the addresses of the first hop
designated routers for all the C-sources. Otherwise, the first hop
routers might not be able to send PIM Register messages to the C-RPs,
and the C-RPs might not be able to send PIM Register-Stop messages to
the first hop routers.
While this extended community allows a customer to inform the SP
dynamically that certain routes are "extranet routes", it does not
allow a customer to control the set of RTs that the route will carry
when it is redistributed as a VPN-IP route. Thus it is only useful
when all the extranet routes from a given VRF are exported with
exactly the same set of RTs. (Cf. section 4.3.1 of [L3VPN], which
does provide a mechanism that, if properly supported by the SP,
allows the customer to determine the set of RTs carried by a VPN-IP
route.)
Note that misconfiguration on the CE router can result in the
Extranet Source extended community being mistakenly attached to a
route that is not intended to be exported as an extranet route. This
could result in a VPN security violation.
4.4.2. Distribution of Extranet Source Extended Community
When a PE receives from a CE a route with the Extranet Source
extended community, the corresponding VPN-IP route originated by the
PE MUST carry this extended community.
A Route Reflector MUST NOT add/remove the Extranet Source extended
community from the VPN-IP routes reflected by the Route Reflector,
including the case where VPN-IP routes received via IBGP are
reflected to EBGP peers (inter-AS option (c), see [MVPN] Section 10).
When re-advertising VPN-IP routes, ASBRs MUST NOT add/remove the
Extranet Source extended community from these routes. This includes
inter-AS options (a) and (b) (see [MVPN] Section 10).
When a PE advertises (via BGP) IP routes to a CE, these routes MUST
NOT carry the Extranet Source extended community, unless the PE-CE
connection is actually an inter-AS option (a) connection (see [MVPN]
Section 10). When the PE-CE connection is not an inter-AS option (a)
connection, a CE that receives an IP route with the Extranet Source
extended community MUST remove it from the route before readvertising
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the route.
4.5. The 'Extranet Separation' Extended Community
We define a new transitive opaque extended community, the "Extranet
Separation" extended community. This extended community is used only
when extranet separation is being used. Its value field MUST be set
to zero upon origination, MUST be ignored upon reception, and MUST be
passed unchanged by intermediate routers.
If a VRF has been provisioned to use extranet separation, and if that
VRF has been provisioned to transmit any extranet C-flows on a
P-tunnel that it advertises in an I-PMSI A-D route or a (C-*,C-*)
S-PMSI A-D route, then any UMH-eligible routes that are exported from
that VRF following the procedures of sections 4.1-4.3 MUST carry the
Extranet Separation extended community. In addition, if an I-PMSI
A-D route and/or (C-*,C-*) S-PMSI A-D route, exported from that VRF,
is used to carry extranet traffic, that A-D route MUST also carry the
Extranet Separation extended community. Further details may be found
in sections 7.3, 7.4.4, and 7.4.5.
5. Origination and Distribution of BGP A-D Routes
Except where otherwise specified, this section describes procedures
and restrictions that are independent of the PE-PE C-multicast
control protocol.
5.1. Route Targets of UMH-eligible Routes and A-D Routes
Suppose there is an extranet C-flow such that:
- The extranet C-source of that C-flow is in VRF A-1.
- One or more extranet C-receivers of that C-flow are in VRF B-1.
In this case VRF A-1 must export a UMH-eligible route that matches
the extranet C-source address, and VRF B-1 must import that route.
In addition, VRF A-1 must export an Intra-AS I-PMSI A-D route or an
S-PMSI A-D route specifying the P-tunnel through which it will send
the data traffic of the given extranet C-flow, and VRF B-1 must
import that route. If BGP is the PE-PE C-multicast control protocol,
then under certain conditions (as specified in [MVPN-BGP]), VRF A-1
may also need to export a Source Active A-D route specifying that it
contains a source of the given C-flow, and VRF B-1 must import that
Source Active A-D route. That is, in order for VRF B-1 to receive a
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C-flow from, a given extranet C-source contained in VRF A-1, VRF A-1
must export a set of A-D routes that are "about" that source, and VRF
B-1 must import them.
One way to ensure this is to provision an RT that is carried by all
the routes exported from VRF A-1 that are "about" a given extranet
C-source, and to provision this RT as an import RT at any VRF (such
as VRF B-1) that is allowed to receive extranet flows from source.
If the "single PMSI per C-flow" transmission model is being used
(with or without extranet separation), there is a an additional
requirement, stated below, on the way RTs are provisioned, as the RTs
carried by a UMH-eligible route that matches a given extranet
C-source may need to be used to identify the A-D routes that are
"about" that source.
Consider the following scenario:
- IP address S is the address of one system in VPN-A, and of a
different system in VPN-B.
- VRF A-1 on PE1 exports UMH-eligible route R1, which is a matching
route for S.
- VRF A-1 on PE1 exports an A-D route P1 whose PTA identifies a
P-tunnel through which VRF A-1 may send traffic whose C-source is
S, where one of the following conditions holds:
* P1 is an I-PMSI A-D route, OR
* P1 is an S-PMSI A-D route whose NLRI contains (C-*,C-*) or
(C-*,C-G), OR
* P1 is an S-PMSI A-D route whose NLRI contains (C-S,C-G) or
(C-S,C-*), BUT the "single C-source per (C-S,C-G) or
(C-S,C-*) P-tunnel" policy is not provisioned.
* P1 is a Source Active A-D route whose NLRI contains (C-S,C-G)
- VRF B-1 on PE1 exports a UMH-eligible route R2, which is a
matching route for S.
- VRF B-1 on PE1 exports an A-D route P2 whose PTA identifies a
P-tunnel on which VRF B-1 may send traffic whose C-source is S,
where one of the following conditions holds:
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* P2 is an I-PMSI A-D route, OR
* P2 is an S-PMSI A-D route whose NLRI specifies (C-*,C-*) or
(C-*,C-G), OR
* P2 is an S-PMSI A-D whose NLRI specifies (C-S,C-G) or
(C-S,C-*), BUT the "single C-source per (C-S,C-G) or
(C-S,C-*) P-tunnel" policy is not provisioned.
* P2 is a Source Active A-D route whose NLRI contains (C-S,C-G)
As already specified in section 4.1, there MUST NOT be any RT that is
common to both R1 and R2. In addition, the following set of rules
for RT assignment MUST be followed when extranets are supported.
This set of rules supports all the extranet transmission models
described in this specification:
- There MUST NOT be any RT that is carried by both P1 and P2.
- The intersection of the set of RTs carried by P1 and the set of
RTs carried by R1 MUST be non-null, and any VRF that imports both
P1 and R1 MUST be configured with an import RT from this
intersection.
- The intersection of the set of RTs carried by P2 and the set of
RTs carried by R2 MUST be non-null, and any VRF that imports both
P2 and R2 MUST be configured with an import RT from this
intersection.
Suppose VRF C-1 on PE2 imports P1 and R1 from VRF A-1, while also
importing P2 from VRF B-1. Since:
- R1 is VRF C-1's route to S, and
- R1 has an RT in common with P1, and
- R1 has no RT in common with P2
it can be concluded that VRF C-1 should expect that multicast traffic
from S will arrive on the P-tunnel specified in P1. See Sections 6
and 7 for more details on determining the expected P-tunnel for a
given extranet C-flow.
While the assignment of import and export RTs to routes is a
deployment and provisioning issue rather than a protocol issue, it
should be understood that failure to follow these rules is likely to
result in VPN security violations.
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5.2. Considerations for Particular Inclusive Tunnel Types
5.2.1. RSVP-TE P2MP
Suppose a VRF, VRF-S, contains a given extranet C-source C-S, and
that VRF-S advertises in its Intra-AS I-PMSI A-D route a P2MP RSVP-TE
as the P-tunnel to carry (extranet multicast) traffic. Suppose VRF-R
contains an extranet C-receiver that is allowed by policy to receive
extranet flows from C-S. Then the RT(s) carried by the Intra-AS
I-PMSI A-D routes originated by VRF-R must be such that those
Intra-AS I-PMSI A-D routes will be imported into VRF-S. (I.e., In
order for VRF-S to set up the P2MP RSVP-TE P-tunnel, it must know all
the PEs that are leaf nodes of the P-tunnel, and to learn this it
MUST import an Intra-AS I-PMSI A-D route from every VRF that needs to
receive data through that tunnel.)
5.2.2. Ingress Replication
[MVPN] and [MVPN-BGP] specify procedures that allow I-PMSIs to be
instantiated by "ingress replication" (IR). The concept of an IR P-
tunnel, and the procedures for supporting IR P-tunnels, are explained
more fully in [MVPN-IR]. An IR P-tunnel can be thought of as a P2MP
tree in which a packet is transmitted from one node on the tree to
another by being encapsulated and sent through a unicast tunnel.
As discussed in section 2, when I-PMSIs are used to support
extranets, egress PEs MUST have the ability to discard customer
multicast data packets that arrive on the wrong P-tunnel. When I-
PMSIs are instantiated by IR, this implies that the following two
procedures MUST be followed:
1. One of the following three procedures MUST be followed:
a) the "Single Forwarder Selection" procedures of [MVPN]
section 9.1.2,
b) the "Native PIM Methods" procedures of [MVPN] section
9.1.3
c) the unicast encapsulation used to transmit packets along
the IR P-tunnel must be such as to enable the receiving
node to identify the transmitting node (note that this
would not be the case if, e.,g., the unicast tunnels were
MP2P LSPs);
and
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2. If a PE assigns an MPLS label value in the PMSI Tunnel
attribute of an Intra-AS or Inter-AS I-PMSI A-D route that it
originates, that label value MUST NOT appear in the PMSI Tunnel
attribute of any other I-PMSI or S-PMSI A-D route originated by
the same PE.
Failure to follow these procedures would make it impossible to
discard packets that arrive on the wrong P-tunnel, and thus could
lead to duplication of data.
If it is desired to support extranet while also using IR to
instantiate the PMSIs, an alternative is to use (C-*,C-*) S-PMSIs
instead of I-PMSIs. (See [MVPN-WILDCARDS] and Sections 7.2.2, 7.3.2,
and 7.4.4 of this document.) This has much the same effect in the
data plane, and there are no restrictions on the type of unicast
tunnel that can be used for instantiating S-PMSIs.
Section 6.4.5 of [MVPN} describes a way to support VPNs using I-PMSIs
that are instantiated by IR, using no S-PMSIs, but using "explicit
tracking" to ensure that a C-flow goes only to egress PEs that have
receivers for it. This document does not provide procedures to
support extranet using that model.
6. When PIM is the PE-PE C-multicast Control Plane
As specified in [MVPN], when PIM is used as the PE-PE C-multicast
control plane for a particular MVPN, there is an MI-PMSI for that
MVPN, and all the PEs of that MVPN must be able to send and receive
on that MI-PMSI. Associated with each VRF of the MVPN is a PIM
C-instance, and the PIM C-instance treats the MI-PMSI as if it were a
LAN interface. That is, the "ordinary" PIM procedures run over the
MI-PMSI just as they would over a real LAN interface, except that the
data plane and control plane "RPF checks" need to be modified.
Section 5.2 of [MVPN] specifies the RPF check modifications for non-
extranet MVPN service.
For example, suppose that there are two VPNs, VPN-S and VPN-R. In
the absence of extranet support, all the VRFs of VPN-S are connected
via one MI-PMSI (call it "the VPN-S MI-PMSI"), and all the VRFs of
VPN-R are connected via another ("the VPN-R MI-PMSI"). If we want to
provide extranet service in which the extranet C-sources are attached
to some set of VPN-S VRFs, while the extranet C-receivers are
attached to some set of VPN-R VRFs, then we have two choices:
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1. either the VPN-R VRFs need to join the VPN-S MI-PMSI, or
2. the VPN-S VRFs need to join the VPN-R MI-PMSI.
The first choice is used to support the "single PMSI per C-flow"
transmission model. The second choice is used to support the
"multiple PMSIs per C-flow" transmission model.
Procedures for both models are described below.
To support these models, it must be possible to determine which
I-PMSI A-D routes are associated with the VPN-S I-PMSI, and which are
associated with the VPN-R I-PMSI. Procedures are given for assigning
RTs to these routes in a way that makes this determination possible.
Both models allow the use of S-PMSIs to carry multicast data traffic.
If a VRF containing receivers can receive from multiple MI-PMSIs,
each S-PMSI must be uniquely associated with a particular MI-PMSI.
Procedures are given for assigning RTs to these routes in a way that
makes this determination possible.
All the procedures specified in Sections 3-5 still apply.
Note that there are no special extranet procedures for Inter-AS
I-PMSI A-D routes or for Leaf A-D routes. Source Active A-D routes
are not used when PIM is the PE-PE C-multicast protocol.
6.1. Provisioning VRFs with RTs
6.1.1. Incoming and Outgoing Extranet RTs
In the absence of extranet service, suppose that each VRF of a given
VPN, call it VPN-S, is configured with RT-S as its import and export
RT, and that each VRF of a second VPN, call it VPN-R, is configured
with RT-R as its import and export RT. We will refer to RT-S and
RT-R as "non-extranet RTs".
Now suppose that VPN-S contains some extranet C-sources, and VPN-R
contains some extranet C-receivers that are allowed by policy to
receive extranet C-flows from the VPN-S extranet C-sources.
To set up this S-to-R extranet, it is necessary to provision an
additional RT, call it RT-S-to-R, whose value is, in general,
distinct from RT-S and RT-R.
A VPN-S VRF that contains extranet C-sources allowed to transmit to
VPN-R must be configured with RT-S-to-R as an "Outgoing Extranet RT".
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A VPN-R VRF that contains extranet C-receivers allowed to received
from VPN-S must be configured with RT-S-to-R as an "Incoming Extranet
RT".
Note that the terms "Incoming" and "Outgoing" in this context refer
to the direction of multicast data packets relative to the VRF.
The Incoming Extranet RTs and Outgoing Extranet RTs that are
configured for a given VRF serve as import RTs for that VRF. They
also serve as export RTs, but only for specific routes as specified
in section 6.1.2 below.
Note that any VRF that contains both extranet C-sources and extranet
C-receivers MUST be configured with both Outgoing and Incoming
Extranet RTs.
A VRF may be configured with more than one Incoming and/or Outgoing
Extranet RT.
If it happens to be the case that all C-sources in VPN-S are extranet
C-sources allowed to transmit to VPN-R, then VPN-S VRFs may be
configured such that RT-S is both a non-extranet RT and an Outgoing
Extranet RT, and VPN-R VRFs may be configured such that RT-S is an
Incoming Extranet RT.
6.1.2. UMH-eligible Routes and RTs
Suppose R1 is a route, exported from a VPN-S VRF, matching an
extranet C-source that is allowed by policy to transmit to VPN-R.
Then R1 MUST carry the Outgoing Extranet RT used for the S-to-R
extranet. This will cause the route to be imported into the VPN-R
VRFs that have extranet C-receivers that are allowed by policy to
receive from VPN-S.
The rules of Section 4 regarding route targets and ambiguous
addresses still apply.
6.1.3. PIM C-Instance Reverse Path Forwarding Determination
Suppose a PIM control message, call it M, is received by a given VRF
V, from a particular P-tunnel T. In order to process control message
M, the PIM C-instance associated with VRF V may need to do an "RPF
determination" (see section 5.2.2 of RFC 6513) for a particular IP
prefix S. RPF determination is based upon the rules for UMH
selection as specified in section 5.1 of RFC 6513.
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This document adds an additional constraint on the UMH selection
procedure. When doing RPF determination for a PIM control message
received over a P-tunnel, a route matching prefix S is not considered
to be eligible for UMH selection unless there is an RT, call it RT1,
configured as one of V's Outgoing Extranet RTs, such that the
following two conditions both hold:
1. The route matching S is exported from VRF V carrying RT1, and
2. An I-PMSI A-D route advertising P-tunnel T (in its PTA) has
been imported into VRF V, and that I-PMSI A-D route carries
RT1.
6.2. Single PMSI per C-flow Model
In this model, if a VPN-S VRF has extranet multicast C-sources, and a
VPN-R VRF has extranet multicast C-receivers allowed by policy to
receive from the C-sources in the VPN-S VRF, then the VPN-R VRF joins
the MI-PMSI that VPN-S uses for its non-extranet traffic.
6.2.1. Forming the MI-PMSIs
Consider a VPN-S VRF that has extranet C-sources. Per [MVPN], each
VPN-S VRF must originate an Intra-AS I-PMSI A-D route containing a
PMSI Tunnel Attribute (PTA) specifying the P-tunnel to be used as
part of the VPN-S MI-PMSI. In the absence of extranet service, this
route carries the VRF's non-extranet RT, RT-S. When extranet service
is provided (using the "single PMSI per C-flow" model), this route
MUST also carry EACH of the VRF's Outgoing Extranet RTs.
Consider a VPN-R VRF that has extranet C-receivers. Per [MVPN], each
VPN-R VRF must originate an Intra-AS I-PMSI A-D route containing a
PTA specifying the P-tunnel to be used as part of the VPN-R MI-PMSI.
This route carries the VRF's non-extranet RT RT-R. When extranet
service is provided (using the "single PMSI per C-flow" model), the
VPN-R VRF MUST also originate one or more additional Intra-AS I-PMSI
A-D routes. It MUST originate one additional Intra-AS I-PMSI A-D
route for each Incoming Extranet RT with which it has been
configured; each such route will carry exactly one of the configured
Incoming Extranet RTs.
Note that when a VRF originates more than one Intra-AS I-PMSI A-D
route, each of them MUST contain a different RD in its NLRI. In
addition, we add the requirement that any pair of such routes MUST
NOT contain an RT in common.
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A VRF with extranet C-sources MUST join the P-tunnels advertised in
the imported I-PMSI A-D routes that carry its non-extranet RT or any
of its Outgoing Extranet RTs. This set of P-tunnels will be treated
as instantiating a single MI-PMSI, and the associated PIM C-instance
will treat that MI-PMSI as a single LAN, and will run PIM procedures
on that LAN, as specified in [MVPN]. The fact that the MI-PMSI
attaches to VRFs of different VPNs is not known to the PIM C-instance
of the VRF containing the sources.
A VRF with extranet C-receivers MUST join the P-tunnels advertised in
all the imported I-PMSI A-D routes. The set of P-tunnels advertised
in the I-PMSI A-D routes that carry a particular Incoming Extranet RT
are treated as instantiating a particular MI-PMSI. So a VRF with
C-receivers will "see" several MI-PMSIs, one corresponding to the
non-extranet, and as many as one for each configured Incoming
Extranet RT. The PIM C-instance associated with the VRF will treat
each of these MI-PMSIs as a separate LAN interface.
As an example, suppose:
- All VPN-R VRFs are configured with RT-R as a non-extranet import
and export RT,
- VPN-R VRFs with extranet receivers are configured with RT-S-to-R
as an Incoming Extranet RT,
- VPN-S VRFs with extranet transmitters are configured:
* with RT-S as a non-extranet import and export RT
* with a list of IP addresses that are the addresses of the
extranet sources
* with RT-S-to-R as an Outgoing Extranet RT
Then VPN-S VRFs will export UMH-eligible routes matching extranet
C-sources, and these routes will carry both RT-S and RT-S-to-R. Each
VPN-S VRF will also export an Intra-AS I-PMSI A-D route that carries
both RT-S and RT-S-to-R.
VPN-R VRFs will originate and export two Intra-AS I-PMSI A-D routes:
one carrying RT-R, and one carrying RT-S-to-R. The Intra-AS I-PMSI
A-D route with RT-S-to-R will be imported into the VPN-S VRFs.
VPN-R will regard all the I-PMSI A-D routes it has exported or
imported with RT-S-to-R as part of a single MI-PMSI. VPN-R will
regard all the I-PMSI A-D routes it has exported or imported with
RT-R as part of a second MI-PMSI. The PIM C-instance associated with
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a VPN-R VRF will treat the two MI-PMSIs as two separate LAN
interfaces. However, the VPN-S VRFs will regard all the I-PMSI A-D
routes imported with RT-S or RT-S-to-R as establishing only a single
MI-PMSI. One can think of this as follows: the VPN-R VRFs have joined
the VPN-S MI-PMSI, as well as the VPN-R MI-PMSI.
Extranets consisting of more than two VPNs are easily supported as
follows. Suppose there are three VPNs, VPN-A, VPN-B, and VPN-C.
VPN-A and VPN-B have extranet C-sources, and VPN-C contains receivers
for both VPN-A extranet C-sources and VPN-B extranet C-sources. In
this case, the VPN-C VRFs that have receivers for both VPN-A and
VPN-B sources may be provisioned as follows. These VPN-C VRFs may be
provisioned with RT-C as a non-extranet RT, and with RT-A-to-C and
RT-B-to-C as Incoming Extranet RTs. In this case, the VPN-C VRFs
that are so provisioned will originate three Intra-AS I-PMSI A-D
routes (each with a different RD in its NLRI), each of which carries
exactly one of the three RTs just mentioned. The VPN-B VRFs with
extranet C-sources will be provisioned with RT-B-to-C as an Outgoing
Extranet RT, and the VPN-A VRFs are provisioned with RT-A-to-C as an
Outgoing Extranet RT. The result will be that the PIM C-instance
associated with a VPN-C VRF will see three LAN interfaces: one for
the non-extranet, one for each of the two extranets. This
generalizes easily to the case where there are VPN-C receivers in n
different extranets (i.e., receiving extranet flows whose sources are
in n different VPNs).
Suppose again that there are there are three VPNs, VPN-A, VPN-B, and
VPN-C. But in this example, VPN-A is the only one with extranet
sources, while VPN-B and VPN-C both have receivers for the VPN-A
extranet sources. This can be provisioned as either one extranet or
as two.
To provision it as one extranet, the VPN-A VRFs are configured with
one Outgoing Extranet RT, call it "RT-A-extranet". The VPN-B and
VPN-C VRFs with extranet receivers will be provisioned with
RT-A-extranet as Incoming Extranet RT. Thus the VPN-B and VPN-C VRFs
will each originate two Intra-AS I-PMSI A-D routes, one for non-
extranet, and one for the extranet. The Intra-AS I-PMSI A-D route,
from a given VRF, for the extranet will carry RT-A-extranet, but will
not share any RT with the non-extranet A-D routes exported from the
same VRF.
The result is that the VPN-B and VPN-C VRFs each belong to two
MI-PMSIs, one for the extranet and one for the intranet. The MI-PMSI
for the extranet attaches VPN-A VRFs, VPN-B VRFs, and VPN-C VRFs.
Alternatively, one could provision the VPN-A VRFs so that some
UMH-eligible extranet source routes carry an RT which we will call
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"RT-A-to-B", and some carry an RT which we will call "RT-A-to-C".
The VPN-A VRFs would be configured with both of these as Outgoing
Extranet RTs. To allow an extranet flow from a VPN-A source to have
both VPN-B and VPN-C receivers, the UMH-eligible route for that
source would carry both RTs. VPN-B VRFs (but not VPN-C VRFs) would
be provisioned with RT-A-to-B as an Incoming Extranet RT. VPN-C VRFs
(but not VPN-B VRFs) would be provisioned with RT-A-to-C as an an
Incoming Extranet RT.
Following the rules above, if any VPN-A extranet source is to have
both VPN-B and VPN-C receivers, the VPN-B and VPN-C VRFs will each
originate two I-PMSI A-D routes, one for extranet and one for non-
extranet. The single Intra-AS I-PMSI A-D route originated by the
VPN-A VRFs will have both RT-A-to-B and RT-A-to-C among its RTs (as
well as VPN-A's non-extranet RT). The extranet I-PMSI A-D route
originated from a VPN-B VRF would have RT-A-to-B, and the extranet
I-PMSI A-D route originated from a VPN-C VRF would have RT-A-to-C.
If a given VRF contains both extranet C-receivers and extranet
C-sources, the procedures described above still work, as the VRF will
be configured with both Incoming Extranet RTs and Outgoing Extranet
RTs; the VRF functions both as a VPN-S VRF and as a VPN-R VRF.
6.2.2. S-PMSIs
When PIM is used as the PE-PE C-multicast control plane, every S-PMSI
is considered to be part of the "emulated LAN" that "corresponds" to
a particular MI-PMSI.
When the bindings of C-flows to particular S-PMSIs are announced via
S-PMSI Join Messages ([MVPN], Section 7) sent on the MI-PMSI, the
S-PMSI is considered to be part of the same LAN interface as the
corresponding MI-PMSI.
When the bindings of C-flows to particular S-PMSIs are announced via
S-PMSI A-D routes, then any S-PMSI A-D route exported from that VRF
MUST have an RT in common with exactly one of the Intra-AS A-D routes
exported from that VRF, and this MUST be one of the VRF's Outgoing
Extranet RTs. Further, the S-PMSI A-D route MUST NOT have an RT in
common with any other Intra-AS A-D route exported from a VRF on the
same PE. A given S-PMSI A-D route will be considered to "correspond"
to the MI-PMSI of the Intra-AS I-PMSI A-D route (originated from the
same PE) with which it shares an RT.
The MI-PMSI that corresponds to a given S-PMSI is determined as
follows:
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- If there is an Intra-AS I-PMSI A-D route originated by the same
PE that originated the S-PMSI A-D route, and if the those two
routes have an RT in common, and if that RT is one of the VRF's
Incoming Extranet RTs, then the S-PMSI corresponds to the I-PMSI
associated with that Intra-AS I-PMSI A-D route.
- Otherwise, if there is an Inter-AS I-PMSI A-D route originated in
the same AS as the S-PMSI A-D route, and if the those two routes
have an RT in common, and if that RT is one of the VRF's Incoming
Extranet RTs, then the S-PMSI corresponds to the I-PMSI
associated with that Inter-AS I-PMSI A-D route.
- Otherwise, there must be a configuration error (a violation of
the requirements of Sections 3-5 of this document).
When wildcard S-PMSIs are used, the rules given in [MVPN-WILDCARDS]
for determining whether a given S-PMSI A-D route is a "match for
reception" to a given (C-S,C-G) or (C-*,C-G) are modified as follows:
A given S-PMSI A-D route MUST NOT be considered to be a "match
for reception" for a given (C-S,C-G) or (C-*,C-G) state UNLESS
that S-PMSI A-D route "corresponds" (as defined above) to the
MI-PMSI that is the incoming interface for the given state.
The rules given in [MVPN-WILDCARDS] for determining whether a given
S-PMSI A-D route is a "match for transmission" are unchanged.
6.2.3. Sending PIM Control Packets
Suppose a PE, say PE1, receives a PIM Join(S,G) from a CE, over a VRF
interface that is associated with a VPN-R VRF. The PE does the RPF
check for S by looking up S in the VPN-R VRF. The PIM C-instance
associated with that VRF must determine the correct P-tunnel over
which to send a PIM Join(S,G) to other PEs.
To do this, PE1 finds, in the VRF associated with the interface over
which the Join was received, the selected UMH route for S, following
the procedures of section 5.1 of [MVPN]. PE1 determines the set of
RTs carried by that route. PE1 then checks to see if there is an
Intra-AS I-PMSI A-D route, currently originated by PE1, that has an
RT in common with the selected UMH route for S.
If the rules of Sections 3-5 have been followed, each of PE1's
selected UMH routes will share an RT with a single one of PE1's
currently originated Intra-AS I-PMSI A-D routes. If this is so, the
Join is sent on the P-tunnel advertised in the PTA of that route.
Otherwise, the Join MUST NOT be sent.
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In essence, this procedure makes the RPF check for C-S resolve to the
MI-PMSI that is serving as the next hop "interface" to C-S.
If a PE receives a PIM Join(*,G) from a CE, the procedure for doing
the RPF check is the same, except that the selected UMH route will be
a route to the C-RP associated with the C-G group.
6.2.4. Receiving PIM Control Packets
When a PIM C-instance receives a PIM control message from a P-tunnel,
it needs to identify the message's "incoming interface". This
incoming interface is the MI-PMSI of which the P-tunnel is a part.
6.2.5. Sending and Receiving Data Packets
The rules for choosing the PMSI on which to send a multicast data
packet are as specified in [MVPN] and [MVPN-WILDCARDS], with one new
restriction: a VPN-S VRF always transmits a multicast data packet
either on the VPN-S MI-PMSI or on an S-PMSI that corresponds to the
VPN-S MI-PMSI. From the perspective of the PIM C-instance, there is
only one outgoing interface.
When a PIM C-instance receives a multicast data packet from a given
P-tunnel, and that P-tunnel is being used to instantiate an MI-PMSI,
the MI-PMSI of which the P-tunnel is a part (see Sections 6.2.1 and
6.2.2) is considered to be the packet's "incoming interface". If the
packet is received on a P-tunnel that was advertised in an S-PMSI A-D
route, the packet's "incoming interface" is the MI-PMSI to which that
S-PMSI route corresponds, as defined in Section 6.2.2. Ordinary PIM
rules for data plane RPF check apply.
Following ordinary PIM procedures, packets arriving from an
unexpected incoming interface are discarded. This eliminates any
problems due to the ambiguities described in Sections 2.1 and 2.2.
6.3. Multiple PMSIs per C-flow Model
In this model, if a VPN-S VRF has extranet multicast C-sources, and a
VPN-R VRF has extranet multicast C-receivers allowed by policy to
receive from the C-sources in the VPN-S VRF, then the VPN-S VRF joins
the MI-PMSI that VPN-R uses for its non-extranet traffic.
In the "single PMSI per C-flow" transmission model (as described in
Section 6.2), a PE that needs to transmit a multicast data packet to
a set of other PEs transmits the packet on a single PMSI. This means
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that if a packet needs to be transmitted from a VPN-A VRF and
received at a VPN-B VRF and a VPN-C VRF, there must be some P-tunnel
from which the VPN-B and VPN-C VRFs can both receive packets.
In the "multiple PMSIs per C-flow" transmission model, a PE that
needs to transmit a multicast data packet to a set of other PEs may
transmit the packet on several different PMSIs. (Of course, any
given packet is transmitted only once on a given P-tunnel.) For
example, if a C-flow (C-S,C-G) has a VPN-A C-source, a VPN-B
receiver, and a VPN-C receiver, there could be one PMSI that the
VPN-A VRF uses to transmit the packet to the VPN-B VRFs, and another
PMSI that the VPN-A VRF uses to transmit the packet to the VPN-C
VRFs.
6.3.1. Forming the MI-PMSIs
Consider a VPN-R VRF that has extranet C-receivers. Per [MVPN], each
VPN-R VRF must originate an Intra-AS I-PMSI A-D route containing a
PMSI Tunnel Attribute (PTA) specifying the P-tunnel to be used as
part of the VPN-R MI-PMSI. In the absence of extranet service, this
route carries the VRF's non-extranet RT, RT-R. When extranet service
is provided (using the "single PMSI per C-flow" model), this route
MUST also carry each of the VRF's Incoming Extranet RTs.
Consider a VPN-S VRF that has extranet C-sources. Per [MVPN], each
VPN-S VRF must originate an Intra-AS I-PMSI A-D route containing a
PTA specifying the P-tunnel to be used as part of the VPN-S MI-PMSI.
This route carries the VRF's non-extranet RT RT-S. When extranet
service is provided using the "multiple PMSI per C-flow" model, the
VPN-S VRF MUST also originate one or more additional Intra-AS I-PMSI
A-D routes. It MUST originate one additional Intra-AS I-PMSI A-D
route for each outgiong extranet RT with which it has been
configured; each such route will have a distinct RD, and will carry
exactly one of the configured Outgoing Extranet RTs.
As with the "single PMSI per C-flow" transmission model, VRFs
containing extranet C-receivers need to import UMH-eligible extranet
C-source routes from VRFs containing C-sources. This is ensured by
the rules of Sections 3-5.
However, in the "multiple PMSIs per C-flow model", a VRF containing
only C-receivers originates only a single Intra-AS I-PMSI A-D route,
carrying the non-extranet RT and all the Incoming Extranet RTs.
When a VRF containing C-receivers imports Intra-AS I-PMSI A-D routes
that carry the non-extranet RT or one of the Incoming Extranet RTs,
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the P-tunnels specified in the PTA of all such routes are considered
to be part of the same MI-PMSI. I.e., the associated PIM C-instance
will treat them as part of a single interface.
In this model, it is the VRF containing extranet C-sources that must
originate multiple Intra-AS I-PMSI A-D routes. Each such route must
have a distinct RD, and the set of RTs carried by any one of these
routes must be disjoint from the set carried by any other. There
must be one such route for each of the VRF's Outgoing Extranet RTs,
and Each such route must carry exactly one of the VRF's Outgoing
Extranet RTs. The VRFs containing extranet C-sources MUST also
import all the A-D routes originated by the VRFs containing extranet
C-receivers. If a set of originated and/or imported Intra-AS I-PMSI
A-D routes have an RT in common, and that RT is one of the VRF's
Outgoing Export RTs, then those routes are considered to be "about"
the same MI-PMSI. The PIM C-instance of the VRF treats each MI-PMSI
as a LAN Interface.
In effect, if VPN-S has only extranet C-sources and VPN-R has only
extranet C-receivers, this model has the VPN-S VRFs join the VPN-R
MI-PMSI. The VPN-S VRFs will thus be attached to multiple MI-PMSIs,
while the VPN-R VRFs are attached to only one. The fact that the
VPN-R MI-PMSI is attached to VPN-S VRFs is not known to the PIM
C-instance at the VPN-R VRFs.
If a VPN-A VRF has extranet C-sources allowed to send to C-receivers
in a VPN-B VRF, and the VPN-B VRF has C-sources allowed to send to
C-receivers in the VPN-A VRF, the above procedures still work as
specified.
Following normal PIM procedures, when the PIM C-instance at a VRF
with extranet C-sources receives a Join(C-S,C-G) or a Join(C-*,C-G)
over an MI-PMSI, it may create (C-S,C-G) or (C-*,C-G) state, and the
MI-PMSI over which the Join was received may be added to the set of
outgoing interfaces for that multicast state. If n MI-PMSIs are
added to the outgoing interface list for a particular multicast
state, a multicast data packet may need to be replicated n times, and
transmitted once on each of the n MI-PMSIs.
Since the all multicast data packets received from another PE are
received over a single emulated LAN, it is not necessary to have any
special procedures to determine a packet's "incoming interface". The
ambiguities described in Section 2.1 and 2.2 do not occur, because a
VPN-R VRF can only receive multicast data traffic that has been
requested by a VPN-R VRF.
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7. When BGP is the PE-PE C-multicast Control Plane
This document assumes that if BGP is used as the PE-PE C-multicast
control plane, the "Single PMSI per C-flow" model is used.
Procedures for providing the "Multiple PMSIs per C-flow" model with
BGP C-multicast are outside the scope of this document.
When BGP is used as the C-multicast control plane, the Single PMSI
per C-flow model may be used either with or without "extranet
separation". (Recall that "extranet separation" means that no
P-tunnel can carry both traffic from extranet sources and traffic
from non-extranet sources.) In either case, the data traffic may be
carried on inclusive tunnels only, or on selective tunnels only
(known as the "S-PMSI only" model), or on a combination of inclusive
and selective tunnels. This is determined by provisioning. The
procedures specified below support all three choices.
Note that there are no special extranet procedures for Inter-AS
I-PMSI A-D routes or for Leaf A-D routes.
7.1. Originating C-multicast Routes
This section applies whether extranet separation is used or not.
When it is necessary to originate a C-multicast Source Tree Join for
(C-S,C-G), a PE must follow the procedures of section 11.1.3
("Constructing the rest of the C-multicast route") of [MVPN-BGP] to
find the selected UMH route for C-S. When it is necessary to
originate a C-multicast Shared Tree Join for (C-*,C-G),where C-G is
an ASM group, a PE must follow the procedures of that section to find
the selected UMH route for C-G's C-RP.
Section 11.1.3 of [MVPN-BGP] specifies how information from the
selected UMH route is used to find an Intra-AS I-PMSI A-D route or an
Inter-AS I-PMSI A-D route. Information from that I-PMSI A-D route is
then used to construct part of the C-multicast route.
For extranet, this specification modifies the procedures of Section
11.1.3 of [MVPN-BGP] as follows. The rules given in section 7.4.5
("I-PMSI A-D Routes") of this document are used to find the Inter-AS
I-PMSI A-D route or an Intra-AS I-PMSI A-D route that "corresponds
to" to the selected UMH route. (That is, the rules of section 7.4.5
of this document replace the rules given in section 11.1.3 of [MVPN-
BGP] for finding the Inter-AS or Intra-AS I-PMSI A-D route.)
Information from this I-PMSI A-D route is then used, as specified in
section 11.1.3 of [MVPN-BGP], to construct the C-multicast route.
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7.2. Originating A-D Routes Without Extranet Separation
7.2.1. Intra-AS I-PMSI A-D Routes
Consider a VRF, call it VRF-S, that contains extranet C-sources, and
that exports UMH-eligible routes matching those C-sources. The VRF
may also originate and export an Intra-AS I-PMSI A-D route.
As specified in [MVPN-BGP], if exactly one Intra-AS I-PMSI A-D route
is originated by and exported from VRF-S, the RTs carried by that
route MUST be chosen such that every VRF that imports a UMH-eligible
route from VRF-S also imports this Intra-AS I-PMSI A-D route.
If inclusive P-tunnels are being used to carry extranet C-flows,
there are additional requirements on the way the RTs carried by the
Intra-AS I-PMSI A-D routes must be chosen, as specified in the
following paragraph.
If VRF-S is using inclusive P-tunnels, but is not using extranet
separation, there is one inclusive P-tunnel rooted at VRF-S, and this
tunnel carries both extranet and non-extranet C-flows. This
inclusive tunnel is identified in the PMSI Tunnel Attribute (PTA) of
the Intra-AS I-PMSI A-D route originated from VRF-S. The set of RTs
carried by this Intra-AS I-PMSI A-D route MUST be chosen so as to
ensure that every VRF that imports a UMH-eligible route from this
VRF-S also imports this Intra-AS I-PMSI A-D route. Further, the set
of RTs carried by this Intra-AS I-PMSI A-D route MUST be chosen such
that it has at least one RT in common with every UMH-eligible route
that is exported from the VRF.
7.2.2. S-PMSI A-D Routes
Let R-SP be an S-PMSI A-D route that is exported from VRF-S. Suppose
that R-SP is used to bind some or all of the extranet C-flows from a
given extranet C-source to a given selective P-tunnel. Let R-UMH be
a UMH-eligible route that is exported from VRF-S and that matches the
given extranet C-source. Then R-SP and R-UMH MUST have at least one
RT in common. Further, the RTs carried by these two routes MUST be
such that every VRF that imports R-UMH also imports R-SP. These
rules apply whether or not R-SP uses wildcards [MVPN-WILDCARDS].
An implementation MUST allow the set of RTs carried by the S-PMSI A-D
routes to be specified by configuration. In the absence of such
configuration, an S-PMSI A-D route originated by a given VRF X MUST
carry a default set of RTs, as specified by the following rules:
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1. By default an S-PMSI A-D route originated by VRF X for a given
(C-S,C-G) or (C-S,C-*) carries the same RT(s) as the
UMH-eligible route originated by VRF X that matches C-S.
2. By default an S-PMSI A-D route originated by VRF X for a given
(C-*,C-G) carries as its RTs a set union of all RT(s) of the
UMH-eligible route(s) matching the multicast C-sources
contained in VRF X that could originate traffic for that C-G.
Moreover, if the VRF contains (as defined in section 1.1) the
C-RP of C-G, then this set union also includes the RT(s) of the
UMH-eligible route matching C-RP, and of the unicast VPN-IP
route matching C-RP.
3. By default, if a (C-*,C-*) S-PMSI A-D route originated by VRF X
is to be used for both extranet and non-extranet traffic, it
carries the same RTs that would be carried (as specified in
section 7.2.1) by an I-PMSI A-D route originated by VRF X if
that I-PMSI A-D route were advertising an inclusive P-tunnel
for carrying both extranet and non-extranet traffic. In
general, a given VRF would not originate both (a) an S-PMSI A-D
route advertising a (C-*,C-*) selective P-tunnel for both
extranet and non-extranet traffic and (b) an I-PMSI A-D route
advertising an inclusive P-tunnel for both extranet and non-
extranet traffic, as the inclusive P-tunnel would not get used
in that case.
7.2.3. Source Active A-D Routes
7.2.3.1. When Inter-Site Shared Trees Are Used
This section applies when Inter-Site Shared Trees are used, as
specified in [MVPN-BGP] section 13.
If VRF-S exports a Source Active A-D route that contains C-S in the
Multicast Source field of its NLRI, and if that VRF also exports a
UMH-eligible route matching C-S, the Source Active A-D route MUST
carry at least one RT in common with the UMH-eligible route. The RT
must be chosen such that the following condition holds: if VRF-R
contains an extranet C-receiver allowed by policy to receive extranet
traffic from C-S, then VRF-R imports both the UMH-eligible route and
the Source Active A-D route.
By default, a Source Active A-D route for a given (C,S,C-G), exported
by a given VRF, carries the same set of RTs as the UMH-eligible route
matching C-S that is exported from that VRF.
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7.2.3.2. When Inter-Site Shared Trees Are Not Used
This section applies when Inter-Site Shared Trees are not used, as
specified in [MVPN-BGP] section 14.
Suppose a VRF, say VRF-X, contains the C-RP for a given extranet
C-group, say C-G. If C-S is an active source for C-G, then following
the procedures of section 14.1 of [MVPN-BGP], VRF-X may export a
Source Active A-D route that contains C-S in the Multicast Source
field of its NLRI. This document replaces the rule for constructing
the RT(s) carried by such a route, specified in section 14.1 of
[MVPN-BGP], with the following. VRF-X MUST be configured such that
the Source Active A-D route for (C-S,C-G) carries the same set of RTs
as the UMH-eligible route matching C-S that is exported from the
VRF(s) containing C-S. This way, if a VRF, say VRF-R, contains an
extranet C-receiver allowed by policy to receive extranet traffic
from C-S, then VRF-R imports both the UMH-eligible route and the
Source Active A-D route.
7.3. Originating A-D Routes With Extranet Separation
If a VRF contains both extranet C-sources and non-extranet C-sources,
it MUST be configured with both a "default RD" and an "extranet RD"
(see section 1.3). The use of these RDs is explained in the
following sub-sections.
7.3.1. Intra-AS I-PMSI A-D Routes
This section applies when VRF-S is using extranet separation, AND
when VRF-S is using an inclusive P-tunnel to carry some or all of the
extranet C-flows that it needs to transmit to other VRFs.
If VRF-S contains both extranet C-sources and non-extranet C-sources,
and if inclusive P-tunnels are used to carry both extranet C-flows
and non-extranet C-flows, then there MUST be two inclusive tunnels
from VRF-S, one of which is to be used only to carry extranet C-flows
(the "extranet inclusive P-tunnel"), and one of which is to be used
only to carry non-extranet C-flows (the "non-extranet inclusive
P-tunnel").
In this case, the VRF MUST originate two Intra-AS I-PMSI A-D routes.
Their respective NLRIs must of course have different RDs. One of the
Intra-AS I-PMSI A-D routes identifies the extranet inclusive P-tunnel
in its PTA. This route must have the VRF's "extranet RD" in its
NLRI. The other route identifies the non-extranet inclusive P-tunnel
in its PTA. This route must have the VRF's "default RD" in its PTA.
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If VRF-S uses an inclusive P-tunnel for carrying extranet traffic,
but does not use an inclusive P-tunnel for carrying non-extranet
traffic, then of course only a single Intra-AS I-PMSI A-D route need
be originated. The PTA of this route identifies the "extranet
inclusive P-tunnel". The NLRI of that route must contain the VRF's
extranet RD.
An Intra-AS I-PMSI A-D route whose PTA identifies an extranet
inclusive P-tunnel MUST carry the Extranet Separation extended
community defined in section 4.5.
The RTs carried by an Intra-AS I-PMSI A-D route whose PTA identifies
the "extranet inclusive P-tunnel" MUST be chosen such that the
following condition holds: if a VRF (call it VRF-R) imports a
UMH-eligible route from VRF-S, and if that route matches an extranet
C-source, then VRF-R also imports that Intra-AS I-PMSI A-D route.
Note that when extranet separation is used, it is possible to use an
inclusive P-tunnel for non-extranet traffic while using only
selective P-tunnels for extranet traffic. It is also possible to use
an inclusive P-tunnel for extranet traffic while using only selective
P-tunnels for non-extranet traffic.
7.3.2. S-PMSI A-D Routes
Let R-SP be an S-PMSI A-D route that is exported from VRF-S. Suppose
that R-SP is used to bind some or all of the extranet C-flows from a
given extranet C-source to a given selective P-tunnel. Let R-UMH be
a UMH-eligible route that is exported from VRF-S and that matches the
given extranet C-source. Then R-SP and R-UMH MUST have at least one
RT in common. Further, the RTs carried by these two routes MUST be
such that every VRF that imports R-UMH also imports R-SP. These
rules apply whether or not R-SP uses wildcards [MVPN-WILDCARDS].
The following rules, specific to the use of extranet separation,
apply:
- A selective P-tunnel MUST NOT carry C-flows from both extranet
and non-extranet C-sources,
- If it is desired to use a (C-*,C-*) S-PMSI to carry extranet
traffic and also to use a (C-*,C-*) S-PMSI to carry non-extranet
traffic, then two (C-*,C-*) S-PMSI A-D routes MUST be originated.
These two routes MUST have different RDs in their respective NLRI
fields, and their respective PTAs MUST identify different
P-tunnels. If the route advertises a P-tunnel that carries only
non-extranet traffic, the route's NLRI MUST contain the VRF's
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default RD. If the route advertises a P-tunnel that carries only
extranet traffic, the route's NLRI MUST contain the VRF's
extranet RD.
- In the following cases, an S-PMSI A-D route exported from the VRF
MUST have the VRF's extranet RD in its NLRI:
* The S-PMSI A-D route is a (C-S,C-G) or a (C-S,C-*) S-PMSI A-D
route, and C-S is an extranet C-source.
* The S-PMSI A-D route is a (C-*,C-G) S-PMSI A-D route, and C-G
is an extranet C-group.
In all other cases, a (C-S,C-G), (C-S,C-*), or (C-*,C-G) S-PMSI
A-D route MUST have the VRF's default RD in its NLRI.
- A (C-*,C-*) S-PMSI A-D route advertising a P-tunnel that is used
to carry extranet traffic MUST carry the Extranet Separation
extended community defined in section 4.5.
An implementation MUST allow the set of RTs carried by the S-PMSI A-D
routes to be specified by configuration. In the absence of such
configuration, an S-PMSI A-D route originated by a given VRF X MUST
carry a default set of RTs, as specified by the following rules:
1. Rule 1 of section 7.2.2 applies.
2. By default, if C-G is an extranet C-group, rule 2 of section
7.2.2 applies.
3. By default, if a (C-*,C-*) S-PMSI A-D route originated by VRF X
is to be used for extranet traffic, it carries the same RTs
that would be carried (as specified in section 7.3.1) by an
I-PMSI A-D route originated by VRF X if that I-PMSI A-D route
were advertising an inclusive P-tunnel for carrying extranet
traffic. In general, a given VRF would not originate both an
S-PMSI A-D route advertising a (C-*,C-*) selective P-tunnel for
extranet traffic and an I-PMSI A-D route advertising an
inclusive P-tunnel for extranet traffic, as the inclusive
P-tunnel would not get used in that case.
7.3.3. Source Active A-D Routes
The procedures of Section 7.2.3 apply.
However, if a Source Active A-D route is exported from a given VRF,
and the route contains C-S, where C-S is an extranet C-source, then
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the RD of the route's NLRI MUST be the extranet RD of the VRF.
Otherwise the RD is the default RD of the VRF.
7.4. Determining the Expected P-tunnel for a C-flow
This section applies whether extranet separation is used or not.
In the context of a VRF with receivers for a particular C-flow, a PE
must determine the P-tunnel over which packets of that C-flow are
expected to arrive. This is done by finding an I-PMSI or S-PMSI A-D
route that "matches" the flow. The matching A-D route will contain a
PTA that specifies the P-tunnel being used to carry the traffic of
that C-flow. We will refer to this P-tunnel as the "expected
P-tunnel" for the C-flow. (Note that, per [MVPN-IR], if the PTA
specifies an tunnel of type "Ingress Replication" (IR), the
identifier of the P-tunnel is actually the NLRI of the I-PMSI or
S-PMSI A-D route. If the PTA specifies a tunnel type other than IR,
the identifier of the P-tunnel is found in the "tunnel identifier"
field of the PTA.)
A PE that needs to receive a given (C-S,C-G) or (C-*,C-G) C-flow MUST
join the expected P-tunnel for that C-flow, and the PE MUST remain
joined to the P-tunnel as long as the PE continues to need to receive
the given C-flow, and the P-tunnel continues to remain the expected
P-tunnel for that C-flow. Procedures for joining and leaving a
tunnel depend, of course, on the tunnel type.
If a PTA specifies a non-zero MPLS label for a tunnel that is not an
IR tunnel, then the PE originating the A-D route containing that PTA
is advertising an aggregate P-tunnel. The aggregate P-tunnel can be
thought of as an outer P-tunnel multiplexing some number of inner
P-tunnels. The inner P-tunnels are demultiplexed by means of the
MPLS label in the PTA. In this document, when we talk of the
"expected P-tunnel" in the context of an aggregate P-tunnel, we refer
to a particular inner P-tunnel, not to the outer P-tunnel. It is
this "inner P-tunnel" that is the expected P-tunnel for a given
C-flow.
In order to find the expected P-tunnel for a given C-flow, the
upstream PE of the C-flow is first determined. Then the S-PMSI A-D
routes originated by that PE are examined, and their NLRIs compared
to the (C-S/C-RP,C-G) of the flow, to see if there is a "match for
reception". (If there is no S-PMSI A-D route that matches a given C-
flow, the expected P-tunnel for that C-flow may have been advertised
in an I-PMSI A-D route; see section 7.4.5.)
The rules for determining, in non-extranet cases, whether a given
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C-flow is a "match for reception" for a given S-PMSI A-D route are
given in [MVPN-WILDCARDS] Section 3.2. Note that we use the terms
"installed" and "originated" as they are defined in [MVPN-WILDCARDS]
Section 3.2. (See also Section 1.1 of this document.)
This specification adds additional rules for determining whether a
given S-PMSI A-D route is a "match for reception" for a given
(C-S/C-RP,C-G). Note that these rules all assume the context of a
particular VRF into which the A-D route has been imported.
The rules given in [MVPN-WILDCARDS] for determining whether a given
S-PMSI A-D route is a "match for transmission" remain unchanged.
Suppose a PE has originated a C-multicast Shared Tree Join for
(C-*,C-G), has not originated a C-multicast Source Tree Join for (C-
S,C-G), but has received and installed a Source Active A-D route for
(C-S,C-G). As described in section 13.2 of [MVPN-BGP], the PE must
receive the (C-S,C-G) traffic from the tunnel the originator of the
installed Source Active A-D route uses for sending (C-S,C-G).
The originator of the installed Source Active A-D route is determined
as follows:
1. Look at the "UMH Route Candidate Set" for C-S, as defined in
[MVPN] section 5.1.3.
2. From that set select a subset of UMH routes to C-S, such that
each route in the subset has at least one RT in common with the
Source Active A-D route, and at least one of the RTs in common
is an import RT of the VRF.
3. From that subset, find the route whose RD is the same as the RD
from the NLRI of the Source Active A-D route.
4. The Upstream PE is the PE identified in the VRF Route Import
Extended Community of that route.
5. The Upstream AS is the AS identified in the Source AS Extended
Community of that route.
If the result of step 2 is an empty set, or if step 3 fails to find a
route, then the Upstream PE of the Source Active A-D route cannot be
determined, and it is necessary to act as if the Source Active A-D
route had not been installed. (A subsequent change to the UMH Route
Candidate Set for C-S may require that a new attempt be made to
determine the Upstream PE.)
Once the upstream PE is determined, the P-tunnel over which the flow
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is expected is determined according to the procedures already
described in this section.
7.4.1. (C-S,C-G) S-PMSI A-D Routes
When extranet functionality is being provided, an S-PMSI A-D route
whose NLRI contains (C-S,C-G) is NOT considered to be a "match for
reception" for a given C-flow (C-S,C-G) unless one of the following
conditions holds (in addition to the conditions specified in
[MVPN-WILDCARDS]):
- the "single C-source per (C-S,C-G) or (C-S,C-*) P-tunnel" is
provisioned, or
- the selected UMH route for C-S has at least one RT in common with
the S-PMSI A-D route, and at least one of the common RTs is an
import RT of the VRF.
7.4.2. (C-S,C-*) S-PMSI A-D Routes
When extranet functionality is being provided, an S-PMSI A-D route
whose NLRI contains (C-S,C-*) is NOT considered to be a "match for
reception" for a given C-flow (C-S,C-G) unless one of the following
conditions holds, in addition to the conditions specified in
[MVPN-WILDCARDS]:
- the "single C-source per (C-S,C-G) or (C-S,C-*) P-tunnel" is
provisioned, or
- the selected UMH route for C-S has at least one RT in common with
the S-PMSI A-D route, and at least one of the common RTs is an
import RT of the VRF.
7.4.3. (C-*,C-G) S-PMSI A-D Routes
When extranet functionality is being provided, an S-PMSI A-D route
whose NLRI contains (C-*,C-G) is NOT considered to be a "match for
reception" for a given C-flow (C-S,C-G) in a given VRF unless either
condition 1 or condition 2 below holds, in addition to the conditions
specified in [MVPN-WILDCARDS]:
1. The given VRF has currently originated a C-multicast Shared
Tree Join route for (C-*,C-G), and
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a) (C-*,C-G) matches an installed (C-*,C-G) S-PMSI A-D route
(according to [MVPN-WILDCARDS]) in the given VRF, and
b) either
i) the "Single C-group per (C-*,C-G) P-tunnel"
policy has been provisioned, or
ii) the RTs of that S-PMSI A-D route form a non-empty
intersection with the RTs carried in the VRF's
selected UMH route for C-RP of that C-G, or
iii) installed in the VRF is at least one (C-S,C-G)
Source Active A-D route that was originated by
the same PE as the (C-*,C-G) S-PMSI A-D route.
2. The given VRF does not have a currently originated C-multicast
Shared Tree Join for (C-*,C-G), but
a) there are one or more values for C-S for which the VRF
has a currently originated Source Tree Join C-multicast
route for (C-S,C-G), and
b) the (C-* C-G) S-PMSI A-D route matches (according to
[MVPN-WILDCARDS]) each such (C-S,C-G), and
c) either
i) the "Single C-group per (C-*,C-G) P-tunnel"
policy has been provisioned, or
ii) the RTs of that S-PMSI A-D route form a non-empty
intersection with the RTs carried in the VRF's
selected UMH routes for each such C-S
If a VRF has an installed (C-*,C-G) S-PMSI A-D route, but does
not have a (C-S,C-G) or (C-*,C-G) multicast state that matches
that route for reception, the procedures of section 12.3
("Receiving S-PMSI A-D Routes by PEs") of [MVPN-BGP] are not
invoked for that route. If those multicast states are created
at some later time when the route is still installed, the
procedures of section 12.3 of [MVPN-BGP] are invoked at that
time.
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7.4.4. (C-*,C-*) S-PMSI A-D Routes
A (C-*,C-*) S-PMSI A-D Route (call it "R-AD") is NOT considered to be
a match for reception for a given C-flow (C-S,C-G) or (C-*,C-G)
unless the following conditions hold (in addition to the conditions
specified in [MVPN-WILDCARDS)]:
- the selected UMH route (call it "R-UMH") for C-S or for C-G's
C-RP respectively has at least one RT in common with R-AD, and at
least one of the common RTs is an import RT of the VRF.
- either R-AD and R-UMH both carry the Extranet Separation extended
community, or neither carries the Extranet Separation extended
community.
7.4.5. I-PMSI A-D Routes
If a particular egress VRF in a particular egress PE contains no
matching S-PMSI A-D routes for a particulalr C-flow, then the C-flow
is expected to arrive (at that egress VRF) on an inclusive P-tunnel.
Suppose that an egress PE has originated a (C-S,C-G) C-Multicast
Source Tree Join. Let R-UMH be the selected UMH route (in the given
egress VRF) or C-S. As specified in [MVPN-BGP], the selected
upstream PE for (C-S,C-G) is determined from the VRF Route Import RT
of R-UMH, and the "selected upstream AS" for the flow is determined
from the Source AS Extended Community of R-UMH.
Suppose that an egress PE has originated a (C-*,C-G) C-Multicast
Shared Tree Join, but has not originated a (C-S,C-G) C-Multicast
Source Tree Join. If the egress VRF does not have a (C-S,C-G) Source
Active A-D route installed, the selected upstream PE is determined
from the VRF Route Import EC of the installed UMH-eligible route
matching C-RP, where C-RP is the RP for the group C-G. The selected
upstream AS for the flow is detemined from the Source AS EC of that
route. If the egress VRF does have a (C-S,C-G) Source Active A-D
route installed, the selected upstream PE and upstream AS are
determined as specified in section 7.4. In either case, let R-UMH be
the installed UMH-eligible route matching C-S.
The inclusive P-tunnel that is expected to be carrying a particular
C-flow is found as follows:
- If the selected upstream AS is the local AS, or if segmented
Inter-AS P-tunnels are not being used to instantiate I-PMSIs,
then look in the VRF for an installed Intra-AS I-PMSI A-D route,
R-AD, such that (a) R-AD originated by the selected upstream PE,
(b) R-AD has at least one an RT in common with R-UMH, (c) at
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least one of the common RTs is an import RT of the local VRF, and
(d) either R-AD and R-UMH both carry the Extranet Separation
extended community, or neither carries the Extranet Separation
extended community.
The PTA of R-AD specifies the P-tunnel over which traffic of the
given C-flow is expected.
- If the selected upstream AS is not the local AS, and if segmented
Inter-AS P-tunnels are being used to instantiate I-PMSIs, then
look in the VRF for an installed Inter-AS I-PMSI A-D route, R-AD,
such that (a) the Source AS field of R-AD's NLRI contains the AS
number of the selected upstream AS, (b) R-AD has at least one RT
in common with R-UMH, (c) at least one of the common RTs is an
import RT of the local VRF, and (d) either R-AD and R-UMH both
carry the Extranet Separation extended community, or neither
carries the Extranet Separation extended community.
The PTA of R-AD specifies the P-tunnel over which traffic of the
given C-flow is expected.
7.5. Packets Arriving from the Wrong P-tunnel
Any packets that arrive on a P-tunnel other than the expected
P-tunnel (as defined in Section 7.4) MUST be discarded, unless it is
know that all the packets carried by both P-tunnels are from the same
ingress VRF. (See section 2.3.1 for a more detailed discussion of
when to discard packets from other than the expected P-tunnel.) Note
that packets arriving on the wrong P-tunnel are to be discarded even
if they are arriving from the expected PE.
8. Multiple Extranet VRFs on the same PE
When multiple VRFs that contain extranet receivers for a given
extranet source are present on the same PE, this PE becomes a single
leaf of the P-tunnel used for sending (multicast) traffic from that
source to these extranet receivers. The PE MUST be able to replicate
this traffic to the multiple VRFs. Specific procedures for doing so
are local to the PE, and outside the scope of this document.
Two or more VRFs on the same PE may import the same S-PMSI A-D route.
If this S-PMSI A-D route contains a PTA that has its "Leaf Info
Required" bit set, it may be necessary for the PE to originate a Leaf
A-D route whose NLRI is computed from the NLRI of the S-PMSI A-D
route. (Details are in [MVPN-BGP].) Note that for a given S-PMSI A-
D route, the PE can originate only one corresponding Leaf A-D route,
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even if the S-PMSI A-D route is imported into multiple VRFs. This
Leaf A-D route can thus be thought of as originating from several
VRFs. It MUST NOT be withdrawn by the PE until there are no longer
any VRFs originating it.
[MVPN-BGP] specifies conditions under which a PE originates a
C-Multicast Source Tree Join or a C-Multicast Shared Tree Join, based
on the (*,G) and (S,G) states associated with a given VRF. It also
specifies the procedure for computing the NLRI of each such route.
While a given PE may contain two or more VRFs that have (extranet)
receivers for the same extranet C-flow, the PE cannot originate more
than one BGP route with a given NLRI. If there are multiple VRFs,
each of which has state that is sufficient to cause a given C-
multicast route to be originated, the route can be thought of as
originating from several VRFs. It MUST NOT be withdrawn by the PE
until there is no longer any VRF with multicast state sufficient to
cause the route to be originated.
For a given extranet the site(s) that contain the extranet source(s)
and the site(s) that contain the extranet receiver(s) may be
connected to the same PE. In this scenario, the procedures by which
(multicast) traffic from these sources is delivered to these
receivers is a local matter to the PE, and outside the scope of this
document.
An implementation MUST support multiple extranet VRFs on a PE.
9. IANA Considerations
IANA is requested to allocate two new codepoints from the "Transitive
Opaque Extended Community Sub-Types" Registry:
- A codepoint for "Extranet Source Extended Community"
- A codepoint for "Extranet Separation Extended Community"
10. Security Considerations
The security considerations of [MVPN] and [MVPN-BGP] are applicable.
In general, different VPNs are allowed to have overlapping IP address
spaces, i.e., a host in one VPN may have the same IP address as a
host in another. This is safe because the customer routes from a
given VPN do not pass into other VPNs. Even if there is overlapping
address space among VPNs, the routes that are known at any given VPN
site are unambiguous, as long as the address space of that VPN is
unambiguous. However, this is not necessarily true when extranet
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service is provided. If an extranet C-receiver in VPN-R is to be
able to receive multicast traffic from an extranet C-source in VPN-S,
then the address of the VPN-S extranet C-source must be imported into
one or more VPN-R VRFs. If that address is also the address of a
VPN-R non-extranet C-source, then a system attempting to receive an
extranet C-flow from the VPN-R extranet C-source may instead receive
a non-extranet C-flow from the VPN-S C-source. This would result in
a VPN security violation.
To avoid this, this document specifies that if a route is imported
into a given VRF, all addresses that are match that route must be
unambiguous in the context of that VRF. Improper provisioning of the
RTs may cause this rule to be violated, and hence result in a VPN
security violation.
It is possible that a given multicast C-source is the source of
multiple flows, some of which are intended to be extranet C-flows,
and some of which are intended to be non-extranet flows. However,
the procedures of this document will allow any C-receiver that is
able to receive the extranet C-flows from a given C-source to also
receive the non-extranet C-flows from that source. As a result, VPN
security violations may result if any system is a C-source for both
extranet and non-extranet C-flows. However, the set of C-flows
transmitted by a given C-source is not under the control of the SP.
SPs who offer the extranet MVPN service must make sure that this
potential for VPN security violations is clearly understood by the
customers who administer the C-sources.
This specification does not require that UMH-eligible routes be "host
routes"; they may be less specific routes. So it is possible for the
NLRI of a UMH-eligible route to contain an address prefix that
matches the address of both an extranet C-source and a non-extranet
C-source. If such a route is exported from a VPN-S VRF and imported
by a VPN-R VRF, C-receivers contained in VPN-R will be able to
receive C-flows from the non-extranet C-sources whose addresses match
that route. This may result in VPN security violations. Service
providers who offer the extranet MVPN service must make sure that
this is clearly understood by the customers who administer the
distribution of routes from CE to PE routers.
If the address ambiguities described in Sections 2.1 and 2.2 are not
prohibited by policy, VRFs MUST be able to discard traffic that
arrives on the wrong P-tunnel; otherwise VPN security violations may
occur.
Section 4.4 specifies the OPTIONAL use of a new extended community,
the Extranet Source extended community. Security considerations
regarding the use and distribution of that extended community are
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discussed in that section.
11. Acknowledgments
The authors wish to thank DP Ayyadevara, Robert Kebler, Padmini
Misra, Rayen Mohanty, Maria Napierala, Karthik Subramanian, and Kurt
Windisch for their contributions to this work.
We also wish to thank Lizhong Jin and Rishabh Parekh for their
reviews and comments.
Special thanks to Jeffrey (Zhaohui) Zhang for his careful review and
for providing the ascii art appearing in Section 2.
12. Authors' Addresses
Rahul Aggarwal
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
Email: raggarwa_1@yahoo.com
Yiqun Cai
Microsoft
1065 La Avenida
Mountain View, CA 94043
Email: yiqunc@microsoft.com
Wim Henderickx
Alcatel-Lucent
Email: wim.henderickx@alcatel-lucent.com
Thomas Morin
France Telecom - Orange
2, avenue Pierre-Marzin
22307 Lannion Cedex
France
EMail: thomas.morin@orange.com
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Praveen Muley
Alcatel-Lucent
Email: Praveen.Muley@alcatel-lucent.com
Ray Qiu
1194 North Mathilda Avenue
Sunnyvale, California 94089
Email: rqiu@juniper.net
Yakov Rekhter
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
Email: yakov@juniper.net
Eric C. Rosen
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA, 01719
Email: erosen@cisco.com
IJsbrand Wijnands
Cisco Systems, Inc.
De kleetlaan 6a Diegem 1831
Belgium
Email: ice@cisco.com
13. References
13.1. Normative References
[L3VPN] "BGP/MPLS IP VPNs", E. Rosen, Y. Rekhter, et. al., RFC 4364,
February 2006
[MVPN] "Multicast in MPLS/BGP IP VPNs", E. Rosen, R. Aggarwal, et.
al., RFC 6513, February 2012
[MVPN-BGP] "BGP Encodings and Procedures for Multicast in MPLS/BGP
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IP VPNs", R. Aggarwal, E. Rosen, T. Morin, Y. Rekhter, RFC 6514,
February 2012
[MVPN-WILDCARDS] "Wildcards in Multicast VPN Auto-Discovery Routes",
Rosen, Rekhter, Henderickx, Qiu, RFC 6625, May 2012
[PIM] "Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", Fenner, Handley, Holbrook,
Kouvelas, RFC 4601, August 2006
[RFC2119] "Key words for use in RFCs to Indicate Requirement
Levels.", Bradner, RFC 2119, March 1997
13.2. Informative References
[BIDIR-PIM] "Bidirectional Protocol Independent Multicast", Handley,
Kouvelas, Speakman, Vicisano, RFC 5015, October 2007
[BSR] "Bootstrap Router (BSR) Mechanism for Protocol Independent
Multicast (PIM)", N. Bhaskar, A. Gall, J. Lingard, S. Venaas, RFC
5059, January 2008
[mLDP] "Label Distribution Protocol Extensions for Point-to-
Multipoint and Multipoint-to-Multipoint Label Switched Paths", IJ.
Wijnands, I. Minei, K. Kompella, B. Thomas, RFC 6388, November 2011
[MVPN-IR] "Ingress Replication Tunnels in Multicast VPN", Rosen,
Subramanian, Zhang, draft-rosen-l3vpn-ir-01.txt, April 2014
[RFC3446] "Anycast Rendevous Point (RP) mechanism using Protocol
Independent Multicast (PIM) and Multicast Source Discovery Protocol
(MSDP)", D. Kim, D. Meyer, H. Kilmer, D. Farinacci, RFC 3446, January
2003
[RFC3618], "Multicast Source Discovery Protocol (MSDP)", B. Fenner,
D. Meyer, RFC 3618, October 2003
[RFC4610] "Anycast-RP Using Protocol Independent Multicast (PIM)", D.
Farinacci, Y. Cai, RFC 4610, August 2006
[RSVP-P2MP] "Extensions to Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) for Point-to-Multipoint TE Label Switched Paths
(LSPs)", R. Aggarwal, D. Papadimitriou, S. Yasukawa, RFC 4875, May
2007
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