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Versions: (draft-raggarwa-l3vpn-2547bis-mcast-bgp)
00 01 02 03 04 05 06 07 08 RFC 6514
Network Working Group R. Aggarwal
Internet Draft Juniper Networks
Expiration Date: April 2010
Intended Status: Proposed Standard
E. Rosen
Cisco Systems, Inc.
T. Morin
France Telecom
Y. Rekhter
Juniper Networks
October 1, 2009
BGP Encodings and Procedures for Multicast in MPLS/BGP IP VPNs
draft-ietf-l3vpn-2547bis-mcast-bgp-08.txt
Status of this Memo
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Copyright and License Notice
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than English.
Abstract
This document describes the BGP encodings and procedures for
exchanging the information elements required by Multicast in MPLS/BGP
IP VPNs, as specified in [MVPN].
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Table of Contents
1 Specification of requirements ......................... 4
2 Introduction .......................................... 5
3 Terminology ........................................... 5
4 MCAST-VPN NLRI ........................................ 6
4.1 Intra-AS I-PMSI A-D route ............................. 7
4.2 Inter-AS I-PMSI A-D route ............................. 8
4.3 S-PMSI A-D route ...................................... 8
4.4 Leaf A-D route ........................................ 9
4.5 Source Active A-D route ............................... 10
4.6 C-multicast route ..................................... 11
5 PMSI Tunnel attribute ................................. 12
6 Source AS Extended Community .......................... 14
7 VRF Route Import Extended Community ................... 15
8 PE Distinguisher Labels Attribute ..................... 16
9 MVPN Auto-Discovery/Binding ........................... 17
9.1 MVPN Auto-Discovery/Binding - Intra-AS Operations ..... 17
9.1.1 Originating Intra-AS I-PMSI A-D routes ................ 17
9.1.2 Receiving Intra-AS I-PMSI A-D routes .................. 20
9.2 MVPN Auto-Discovery/Binding - Inter-AS Operations ..... 21
9.2.1 Originating Inter-AS I-PMSI A-D routes ................ 23
9.2.2 When not to originate Inter-AS I-PMSI A-D routes ...... 24
9.2.3 Propagating Inter-AS I-PMSI A-D routes ................ 24
9.2.3.1 Propagating Inter-AS I-PMSI A-D routes - Overview ..... 24
9.2.3.2 Inter-AS I-PMSI A-D route received via EBGP ........... 25
9.2.3.2.1 Originating Leaf A-D route into EBGP .................. 26
9.2.3.3 Leaf A-D route received via EBGP ...................... 27
9.2.3.4 Inter-AS I-PMSI A-D route received via IBGP ........... 28
9.2.3.4.1 Originating Leaf A-D route into IBGP .................. 30
9.2.3.5 Leaf A-D route received via IBGP ...................... 30
9.2.3.6 Optimizing Bandwidth by IP filtering on ASBRs ......... 31
10 Non-congruent Unicast and Multicast Connectivity ...... 32
11 Exchange of C-Multicast Routing Information among PEs . 33
11.1 Originating C-multicast routes by a PE ................ 34
11.1.1 Originating routes: PIM as the C-Multicast protocol ... 34
11.1.1.1 Originating Source Tree Join C-multicast route ........ 34
11.1.1.2 Originating Shared Tree Join C-multicast route ........ 34
11.1.2 Originating routes: mLDP as the C-Multicast protocol .. 35
11.1.3 Constructing the rest of the C-multicast route ........ 35
11.1.4 Unicast Route Changes ................................. 37
11.2 Propagating C-multicast routes by an ASBR ............. 37
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11.3 Receiving C-multicast routes by a PE .................. 38
11.3.1 Receiving routes: PIM as the C-Multicast protocol ..... 39
11.3.1.1 Receiving Source Tree Join C-multicast route .......... 39
11.3.1.2 Receiving Shared Tree Join C-multicast route .......... 40
11.3.2 Receiving routes: mLDP as the C-Multicast protocol .... 40
11.4 C-multicast routes aggregation ........................ 41
12 Using S-PMSI A-D routes to Bind C-trees to P-tunnels .. 42
12.1 Originating S-PMSI A-D routes ......................... 42
12.2 Handling S-PMSI A-D routes by ASBRs ................... 44
12.2.1 Merging S-PMSI into an I-PMSI ......................... 45
12.3 Receiving S-PMSI A-D routes by PEs .................... 46
13 Switching from Shared C-tree to Source C-tree ......... 47
13.1 Source Within a Site - Source Active Advertisement .... 48
13.2 Receiving Source Active A-D route ..................... 49
13.2.1 Pruning Sources off the Shared Tree ................... 50
14 Supporting PIM-SM without Inter-Site Shared C-trees ... 51
14.1 Discovering Active Multicast Sources .................. 51
14.2 Receiver(s) Within a Site ............................. 52
14.3 Receiving C-multicast routes by a PE .................. 54
15 Carrier's Carrier ..................................... 54
16 Scalability Considerations ............................ 54
16.1 Dampening C-multicast routes .......................... 55
16.1.1 Dampening withdrawals of C-multicast routes ........... 56
16.1.2 Dampening Source/Shared Tree Join C-multicast routes .. 57
16.2 Dampening withdrawals of Leaf A-D routes .............. 57
17 Security Considerations ............................... 57
18 IANA Considerations ................................... 58
19 Acknowledgement ....................................... 59
20 Authors' Addresses .................................... 59
21 References ............................................ 59
21.1 Normative References .................................. 59
21.2 Informative References ................................ 60
1. Specification of requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. Introduction
This document describes the BGP encodings and procedures for
exchanging the information elements required by Multicast in MPLS/BGP
IP VPNs, as specified in [MVPN]. This document assumes a thorough
familiarity with procedures, concepts and terms described in [MVPN].
This document defines a new NLRI, MCAST-VPN NLRI. The MCAST-VPN NLRI
is used for MVPN auto-discovery, advertising MVPN to I-PMSI tunnel
binding, advertising (C-S, C-G) to S-PMSI tunnel binding, VPN
customer multicast routing information exchange among PEs, choosing a
single forwarder PE, and for procedures in support of co-locating a
C-RP on a PE.
This document specifies two new BGP attributes, P-Multicast Service
Interface Tunnel (PMSI Tunnel) attribute, and PE Distinguisher Label
attribute.
This document also defines two new BGP Extended Communities, Source
AS Extended Community and VRF Route Import Extended Community.
3. Terminology
In the context of this document we will refer to the MVPN auto-
discovery/binding information carried in BGP as "auto-discovery
routes" ("A-D routes"). For a given MVPN there are the following
types of A-D routes:
+ Intra-AS I-PMSI A-D route;
+ Inter-AS I-PMSI A-D route;
+ S-PMSI A-D route;
+ Leaf A-D route;
+ Source Active A-D route.
In the context of this document we will refer to the MVPN customers
multicast routing information carried in BGP as "C-multicast routes".
For a given MVPN there are the following types of C-multicast routes:
+ Shared Tree Join route;
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+ Source Tree Join route;
For each MVPN present on a PE, the PE maintains a Tree Information
Base (MVPN-TIB). This is the same as TIB defined in [RFC4601], except
that instead of a single TIB a PE maintains multiple MVPN-TIBs, one
per each MVPN.
Throughout this draft we will use the term "VPN-IP route" to mean a
route which is either in the VPN-IPv4 address family [RFC4364] or in
the VPN-IPv6 address family [RFC4659].
4. MCAST-VPN NLRI
This document defines a new BGP NLRI, called the MCAST-VPN NLRI.
Following is the format of the MCAST-VPN NLRI:
+-----------------------------------+
| Route Type (1 octet) |
+-----------------------------------+
| Length (1 octet) |
+-----------------------------------+
| Route Type specific (variable) |
+-----------------------------------+
The Route Type field defines encoding of the rest of MCAST-VPN NLRI
(Route Type specific MCAST-VPN NLRI).
The Length field indicates the length in octets of the Route Type
specific field of MCAST-VPN NLRI.
This document defines the following Route Types for A-D routes:
+ 1 - Intra-AS I-PMSI A-D route;
+ 2 - Inter-AS I-PMSI A-D route;
+ 3 - S-PMSI A-D route;
+ 4 - Leaf A-D route;
+ 5 - Source Active A-D route.
This document defines the following Route Types for C-multicast
routes:
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+ 6 - Shared Tree Join route;
+ 7 - Source Tree Join route;
The MCAST-VPN NLRI is carried in BGP [RFC4271] using BGP
Multiprotocol Extensions [RFC4760] with an AFI of 1 or 2 and an SAFI
of MCAST-VPN. The NLRI field in the MP_REACH_NLRI/MP_UNREACH_NLRI
attribute contains the MCAST-VPN NLRI (encoded as specified above).
The value of the AFI field in the MP_REACH_NLRI/MP_UNREACH_NLRI
attribute that carries the MCAST-VPN NLRI determines whether the
Multicast Source and Multicast Group addresses carried in the S-PMSI
A-D routes, Source Active A-D routes, and C-multicast routes are IPv4
or IPv6 addresses (AFI 1 indicates IPv4 addresses, AFI 2 indicates
IPv6 addresses).
In order for two BGP speakers to exchange labeled MCAST-VPN NLRI,
they must use BGP Capabilities Advertisement to ensure that they both
are capable of properly processing such NLRI. This is done as
specified in [RFC4760], by using capability code 1 (multiprotocol
BGP) with an AFI of 1 or 2 and an SAFI of MCAST-VPN.
The following describes the format of the Route Type specific MCAST-
VPN NLRI for various Route Types defined in this document.
4.1. Intra-AS I-PMSI A-D route
An Intra-AS I-PMSI A-D route type specific MCAST-VPN NLRI consists of
the following:
+-----------------------------------+
| RD (8 octets) |
+-----------------------------------+
| Originating Router's IP Addr |
+-----------------------------------+
The RD is encoded as described in [RFC4364].
Usage of Intra-AS I-PMSI A-D routes is described in Section "MVPN
Auto-Discovery/Binding - Intra-AS Operations".
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4.2. Inter-AS I-PMSI A-D route
An Inter-AS I-PMSI A-D route type specific MCAST-VPN NLRI consists of
the following:
+-----------------------------------+
| RD (8 octets) |
+-----------------------------------+
| Source AS (4 octets) |
+-----------------------------------+
The RD is encoded as described in [RFC4364].
The Source AS contains an Autonomous System number.
Two octets AS numbers are encoded in the two low order octets of the
Source AS field, with the the two high order octets set to zero.
Usage of Inter-AS I-PMSI A-D routes is described in Section "MVPN
Auto-Discovery/Binding - Inter-AS Operations".
4.3. S-PMSI A-D route
An S-PMSI A-D route type specific MCAST-VPN NLRI consists of the
following:
+-----------------------------------+
| RD (8 octets) |
+-----------------------------------+
| Multicast Source Length (1 octet) |
+-----------------------------------+
| Multicast Source (Variable) |
+-----------------------------------+
| Multicast Group Length (1 octet) |
+-----------------------------------+
| Multicast Group (Variable) |
+-----------------------------------+
| Originating Router's IP Addr |
+-----------------------------------+
The RD is encoded as described in [RFC4364].
The Multicast Source field contains the C-S address. If the Multicast
Source field contains an IPv4 address, then the value of the
Multicast Source Length field is 32. If the Multicast Source field
contains an IPv6 address, then the value of the Multicast Source
Length field is 128.
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The Multicast Group field contains the C-G address or C-LDP MP Opaque
Value Element (use of C-LDP MP Opaque Value Element is described in
Section "Receiving routes: mLDP as the C-Multicast protocol"). If the
Multicast Group field contains an IPv4 address, then the value of the
Multicast Group Length field is 32. If the Multicast Group field
contains an IPv6 address, then the value of the Multicast Group
Length field is 128.
Usage of other values of the Multicast Source Length and Multicast
Group Length fields is outside the scope of this document.
Usage of S-PMSI A-D routes is described in Section "Using S-PMSI A-D
routes to Bind C-trees to P-tunnels".
4.4. Leaf A-D route
A Leaf A-D route type specific MCAST-VPN NLRI consists of the
following:
+-----------------------------------+
| Route Key (variable) |
+-----------------------------------+
| Originating Router's IP Addr |
+-----------------------------------+
Leaf A-D routes may be originated as a result of processing a
received Inter-AS I-PMSI A-D route or S-PMSI A-D route. A Leaf A-D
route is originated in these situations only if the received route
has a PMSI Tunnel attribute whose "Leaf Information Required" bit is
set to 1.
If a Leaf A-D route is originated as a result of processing one of
the received routes specified in the previous paragraph, the Route
Key of the Leaf A-D route is set to the NLRI of the received route.
Details of the use of the Leaf A-D route may be found in Sections
"Originating Leaf A-D route into EBGP", "Leaf A-D route received via
EBGP", "Originating Leaf A-D route into IBGP", "Leaf A-D route
received via IBGP", and "Receiving S-PMSI A-D routes by PEs".
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4.5. Source Active A-D route
A Source Active A-D route type specific MCAST-VPN NLRI consists of
the following:
+-----------------------------------+
| RD (8 octets) |
+-----------------------------------+
| Multicast Source Length (1 octet) |
+-----------------------------------+
| Multicast Source (Variable) |
+-----------------------------------+
| Multicast Group Length (1 octet) |
+-----------------------------------+
| Multicast Group (Variable) |
+-----------------------------------+
The RD is encoded as described in [RFC4364].
The Multicast Source field contains the C-S address. If the Multicast
Source field contains an IPv4 address, then the value of the
Multicast Source Length field is 32. If the Multicast Source field
contains an IPv6 address, then the value of the Multicast Source
Length field is 128.
Use of the Source Active A-D routes with the Multicast Source Length
field of 0 is outside the scope of this document.
The Group Address field contains the C-G address. If the Multicast
Group field contains an IPv4 address, then the value of the Multicast
Group Length field is 32. If the Multicast Group field contains an
IPv6 address, then the value of the Multicast Group Length field is
128.
Source Active A-D routes with a Multicast group belonging to the
Source Specific Multicast (SSM) range (as defined in [RFC4607], and
potentially extended locally on a router) MUST NOT be advertised by a
router and MUST be discarded if received.
Usage of Source Active A-D routes is described in Sections "Switching
from Shared C-tree to Source C-tree", and "Supporting PIM-SM without
Inter-Site Shared C-trees".
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4.6. C-multicast route
A Shared Tree Join route and a Source Tree Join route type specific
MCAST-VPN NLRI consists of the following:
+-----------------------------------+
| RD (8 octets) |
+-----------------------------------+
| Source AS (4 octets) |
+-----------------------------------+
| Multicast Source Length (1 octet) |
+-----------------------------------+
| Multicast Source (Variable) |
+-----------------------------------+
| Multicast Group Length (1 octet) |
+-----------------------------------+
| Multicast Group (Variable) |
+-----------------------------------+
The RD is encoded as described in [RFC4364].
The Source AS contains an Autonomous System number. Two octets AS
numbers are encoded in the low order two octets of the Source AS
field.
For a Shared Tree Join route the Multicast Source field contains the
C-RP address; for a Source Tree Join route the Multicast Source field
contains the C-S address. If the Multicast Source field contains an
IPv4 address, then the value of the Multicast Source Length field is
32. If the Multicast Source field contains an IPv6 address, then the
value of the Multicast Source Length field is 128.
The Group Address field contains the C-G address or C-MP Opaque Value
Element. If the Multicast Group field contains an IPv4 address, then
the value of the Multicast Group Length field is 32. If the
Multicast Group field contains an IPv6 address, then the value of the
Multicast Group Length field is 128.
Usage of C-multicast routes is described in Section "Exchange of C-
Multicast Routing Information among PEs".
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5. PMSI Tunnel attribute
This document defines and uses a new BGP attribute, called P-
Multicast Service Interface Tunnel (PMSI Tunnel) attribute. This is
an optional transitive BGP attribute. The format of this attribute is
defined as follows:
+---------------------------------+
| Flags (1 octet) |
+---------------------------------+
| Tunnel Type (1 octets) |
+---------------------------------+
| MPLS Label (3 octets) |
+---------------------------------+
| Tunnel Identifier (variable) |
+---------------------------------+
The Flags field has the following format:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| reserved |L|
+-+-+-+-+-+-+-+-+
This document defines the following flags:
+ Leaf Information Required (L)
The Tunnel Type identifies the type of the tunneling technology used
to establish the PMSI tunnel. The type determines the syntax and
semantics of the Tunnel Identifier field. This document defines the
following Tunnel Types:
+ 0 - No tunnel information present
+ 1 - RSVP-TE P2MP LSP
+ 2 - mLDP P2MP LSP
+ 3 - PIM-SSM Tree
+ 4 - PIM-SM Tree
+ 5 - PIM-Bidir Tree
+ 6 - Ingress Replication
+ 7 - mLDP MP2MP LSP
If the MPLS Label field is non-zero, then it contains an MPLS label
encoded as 3 octets, where the high-order 20 bits contain the label
value. Absence of MPLS Label is indicated by setting the MPLS Label
field to zero.
When the type is set to "No tunnel information present", the PMSI
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Tunnel attribute carries no tunnel information (no Tunnel
Identifier). This type is to be used only in the following case: to
enable explicit tracking for a particular customer multicast flow (by
setting the Leaf Information Required flag to 1), but without binding
this flow to a particular provider tunnel (by omitting any tunnel
information).
When the type is set to RSVP-TE P2MP LSP, the Tunnel Identifier is
<Extended Tunnel ID, Reserved, Tunnel ID, P2MP ID> as carried in the
RSVP-TE P2MP LSP SESSION Object [RFC4875].
When the type is set to mLDP P2MP LSP, the Tunnel Identifier is a
P2MP FEC Element [mLDP].
When the type is set to PIM-SM Tree, the Tunnel Identifier is <Sender
Address, P-Multicast Group>. The node that originated the attribute
MUST use the address carried in the Sender Address as the source IP
address for the IP/GRE encapsulation of the MVPN data.
When the type is set to PIM-SSM Tree, the Tunnel Identifier is <P-
Root Node Address, P-Multicast Group>. The node that originates the
attribute MUST use the address carried in the P-Root Node Address as
the source IP address for the IP/GRE encapsulation of the MVPN data.
The P-Multicast Group element of the Tunnel identifier of the Tunnel
attribute MUST NOT be expected to be the same group for all Intra-AS
A-D routes for the same MVPN. According to [RFC4607], the group
address can be locally allocated by the originating PE without any
consideration for the group address used by other PE on the same
MVPN.
When the type is set to PIM-Bidir Tree, the Tunnel Identifier is
<Sender Address, P-Multicast Group>. The node that originated the
attribute MUST use the address carried in the Sender Address as the
source IP address for the IP/GRE encapsulation of the MVPN data.
When the type is set to PIM-SM or PIM-Bidir tree, then the P-
Multicast group element of the Tunnel identifier of the Tunnel
attribute SHOULD be the same multicast group address for all Intra-AS
I-PMSI A-D routes for the same MVPN originated by PEs within a given
AS. How this multicast group address is chosen is outside the scope
of this specification.
When the type is set to Ingress Replication the Tunnel Identifier
carries the unicast tunnel endpoint IP address of the local PE that
is to be this PE's receiving endpoint address for the tunnel.
When the type is set to mLDP MP2MP LSP, the Tunnel Identifier is an
MP2MP FEC Element [mLDP].
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The use of mLDP MP2MP LSPs as Provider tunnels (P-tunnels) requires
procedures which are outside the scope of this document.
A router that supports the PMSI Tunnel attribute considers this
attribute to be malformed if it either (a) contains an undefined
Tunnel Type, or (b) the router can not parse the Tunnel Identifier
field of the attribute as a tunnel identifier of the tunnel types
specifed in the Tunnel Type field of the attribute.
When a router that receives a BGP Update that contains the PMSI
Tunnel attribute with its Partial bit set determines that the
attribute is malformed, the router SHOULD treat this Update as though
all the routes contained in this Update had been withdrawn.
An implementation MUST provide debugging facilities to permit issues
caused by malformed PMSI Tunnel attribute to be diagnosed. At a
minimum, such facilities MUST include logging an error when such an
attribute is detected.
The PMSI Tunnel attribute is used in conjunction with Intra-AS I-PMSI
A-D routes, Inter-AS I-PMSI A-D routes, S-PMSI A-D routes, and Leaf
A-D routes.
6. Source AS Extended Community
This document defines a new BGP extended community called Source AS.
The Source AS is an AS specific extended community, of an extended
type, and is transitive across AS boundaries [RFC4360].
The Global Administrator field of this community MUST be set to the
autonomous system number of the PE. The Local Administrator field of
this community MUST be set to 0.
If for a given MVPN BGP is used for exchanging C-multicast routes, or
if segmented inter-AS tunnels are used, then when a PE that has sites
of that MVPN connected to it originates a (unicast) route to VPN-IP
addresses, the PE MUST include in the BGP Update message that carries
this route the Source AS extended community.
The usage of a received Source AS extended community is described in
Section "Constructing the rest of the C-multicast route".
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7. VRF Route Import Extended Community
This document defines a new BGP extended community called VRF Route
Import.
The VRF Route Import is an IP address specific extended community, of
an extended type, and is transitive across AS boundaries [RFC4360].
To support MVPN in addition to the import/export Route Target(s)
extended communities used by the unicast routing, each VRF on a PE
MUST have an import Route Target extended community, except if it is
known a priori that none of the (local) MVPN sites associated with
the VRF contain multicast source(s) and/or C-RP, in which case the
VRF need not have this import Route Target.
We refer to this Route Target as the "C-multicast Import RT", as this
Route Target controls imports of C-multicast routes into a particular
VRF.
A PE constructs C-multicast Import RT as follows:
+ The Global Administrator field of the C-multicast Import RT MUST
be set to an IP address of the PE. This address SHOULD be common
for all the VRFs on the PE (e.,g., this address may be PE's
loopback address).
+ The Local Administrator field of the C-multicast Import RT
associated with a given VRF contains a 2 octets long number that
uniquely identifies that VRF within the PE that contains the VRF
(procedures for assigning such numbers are purely local to the
PE, and outside the scope of this document).
The way C-multicast Import RT is constructed, it uniquely identifies
a VRF.
A PE that has site(s) of a given MVPN connected to it needs to
communicate the value of the C-multicast Import RT associated with
the VRF of that MVPN on the PE to all other PEs that have sites of
that MVPN. To accomplish this a PE that originates a (unicast) route
to VPN-IP addresses MUST include in the BGP Updates message that
carries this route the VRF Route Import extended community that has
the value of the C-multicast Import RT of the VRF associated with the
route, except if it is known a priori (e.g., via provisioning) that
none of these addresses could act as multicast sources and/or RP, in
which case the (unicast) route MUST NOT carry the VRF Route Import
extended community.
If a PE uses Route Target Constrain [RT-CONSTRAIN], the PE SHOULD
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advertise all such C-multicast Import RTs using Route Target
Constrains (note that doing this requires just a single Route Target
Constraint advertisement by the PE). This allows each C-multicast
route to reach only the relevant PE. To constrain distribution of the
Route Target Constrain routes to the AS of the advertising PE these
routes SHOULD carry the NO_EXPORT Community ([RFC1997]).
Usage of VRF Route Import extended community is described in Section
"Constructing the rest of the C-multicast route".
8. PE Distinguisher Labels Attribute
This document defines a new BGP attribute, called PE Distinguisher
Labels attribute. This is an optional transitive BGP attribute. The
format of this attribute is defined as follows:
+---------------------------------+
| PE Address |
+---------------------------------+
| Label (3 octets) |
+---------------------------------+
.......
+---------------------------------+
| PE Address |
+---------------------------------+
| Label (3 octets) |
+---------------------------------+
The Label field contains an MPLS label encoded as 3 octets, where the
high-order 20 bits contain the label value.
A router that supports the PE Distinguisher Labels attribute
considers this attribute to be malformed if the PE Address field does
not contain a unicast address. The attribute is also considered to be
malformed if the PE Address field is expected to be an IPv4 address,
and the length of the attribute minus 4 is not a multiple of 3, or
the PE Address field is expected to be an IPv6 address, and the
length of the attribute minus 16 is not a multiple of 3. (The length
of the Route Type field of MCAST-VPN NLRI of the route that carries
the PE Distinguisher Labels attribute provides the information on
whether the PE Address field contains an IPv4 or IPv6 address.)
When a router that receives a BGP Update that contains the PE
Distinguisher Labels attribute with its Partial bit set determines
that the attribute is malformed, the router SHOULD treat this Update
as though all the routes contained in this Update had been withdrawn.
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An implementation MUST provide debugging facilities to permit issues
caused by malformed PE Distinguisher Label attribute to be diagnosed.
At a minimum, such facilities MUST include logging an error when such
an attribute is detected.
Usage of this attribute is described in [MVPN].
9. MVPN Auto-Discovery/Binding
This section specifies procedures for the auto-discovery of MVPN
memberships and the distribution of information used to instantiate
I-PMSIs.
There are two MVPN auto-discovery/binding mechanisms, dubbed "intra-
AS" and "inter-AS" respectively.
The intra-AS mechanisms provide auto-discovery/binding within a
single AS.
The intra-AS mechanisms also provide auto-discovery/binding across
multiple ASes when non-segmented inter-AS tunnels are being used.
The inter-AS mechanisms provide auto-discovery/binding across
multiple ASes when segmented inter-AS tunnels are being used.
Note that if a multi-AS system uses option (a) of section 10 of
[RFC4364], the notion of inter-AS tunnels does not apply, and so it
needs only the intra-AS mechanisms.
9.1. MVPN Auto-Discovery/Binding - Intra-AS Operations
This section describes exchanges of Intra-AS I-PMSI A-D routes
originated/received by PEs within the same AS, or if non-segmented
inter-AS tunnels are used, then by all PEs.
9.1.1. Originating Intra-AS I-PMSI A-D routes
To participate in the MVPN auto-discovery/binding a PE router that
has a given VRF of a given MVPN MUST, except for the cases specified
further down in this section, originate an Intra-AS I-PMSI A-D route
and advertises this route in IBGP. The route is constructed as
follows.
The route carries a single MCAST-VPN NLRI with the RD set to the RD
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of the VRF, and the Originating Router's IP Address field set to the
IP address that the PE places in the Global Administrator field of
the VRF Route Import extended community of the VPN-IP routes
advertised by the PE. Note that the <RD, Originating Router's IP
address> tuple uniquely identifies a given multicast VRF.
The route carries the PMSI Tunnel attribute if and only if an I-PMSI
is used for the MVPN (the conditions under which an I-PMSI is used
can be found in [MVPN]). Depending on the technology used for the P-
tunnel for the MVPN on the PE, the PMSI Tunnel attribute of the
Intra-AS I-PMSI A-D route is constructed as follows.
+ If the PE that originates the advertisement uses a P-Multicast
tree for the P-tunnel for the MVPN, the PMSI Tunnel attribute
MUST contain the identity of the tree (note that the PE could
create the identity of the tree prior to the actual instantiation
of the tree).
+ A PE that uses a P-Multicast tree for the P-tunnel MAY aggregate
two or more MVPNs present on the PE onto the same tree. In this
case in addition to carrying the identity of the tree, the PMSI
Tunnel attribute MUST carry an MPLS upstream assigned label which
the PE has bound uniquely to the MVPN associated with this update
(as determined by its RTs).
If the PE has already advertised Intra-AS I-PMSI A-D routes for
two or more MVPNs that it now desires to aggregate, then the PE
MUST re-advertise those routes. The re-advertised routes MUST be
the same as the original ones, except for the PMSI Tunnel
attribute and the label carried in that attribute.
+ If the PE that originates the advertisement uses ingress
replication for the P-tunnel for the MVPN, the route MUST include
the PMSI Tunnel attribute with the Tunnel Type set to Ingress
Replication and Tunnel Identifier set to a routable address of
the PE. The PMSI Tunnel attribute MUST carry a downstream
assigned MPLS label. This label is used to demultiplex the MVPN
traffic received over a unicast tunnel by the PE.
+ The Leaf Information Required flag of the PMSI Tunnel attribute
MUST be set to zero, and MUST be ignored on receipt.
Discovery of PE capabilities in terms of what tunnels types they
support is outside the scope of this document. Within a given AS PEs
participating in an MVPN are expected to advertise tunnel bindings
whose tunnel types are supported by all other PEs that are
participating in this MVPN and are part of the same AS. In addition,
in the inter-AS scenario with non-segmented inter-AS tunnels, the
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tunnel types have to be supported by all PEs that are participating
in this MVPN, irrespective of whether these PEs are in the same AS or
not.
The Next Hop field of the MP_REACH_NLRI attribute of the route MUST
be set to the same IP address as the one carried in the Originating
Router's IP Address field.
By default the distribution of the Intra-AS I-PMSI A-D routes is
controlled by the same Route Targets as the ones used for the
distribution of VPN-IP unicast routes. That is, by default the Intra-
AS I-PMSI A-D route MUST carry the export Route Target used by the
unicast routing. If any other PE has one of these Route Targets
configured as an import Route Target for a VRF present on the PE, it
treats the advertising PE as a member in the MVPN to which the VRF
belongs. The default could be modified via configuration by having a
set of Route Targets used for the Intra-AS I-PMSI A-D routes being
distinct from the ones used for the VPN-IP unicast routes (see also
Section "Non-congruent Unicast and Multicast Connectivity").
To constrain distribution of the intra-AS membership/binding
information to the AS of the advertising PE the BGP Update message
originated by the advertising PE SHOULD carry the NO_EXPORT Community
([RFC1997]).
Note that if non-segmented inter-AS P-tunnels are being used, then
the Intra-AS I-PMSI routes need to be distributed to other ASes and
MUST NOT carry the NO_EXPORT community.
When BGP is used to exchange C-multicast routes, if (a) it is known a
priori that as a matter of policy none of the MVPN sites connected to
a given PE are allowed to send multicast traffic to other sites of
that MVPN (in other words, all these sites are only in the Receiver
Sites set), (b) the PE does not use ingress replication for the
incoming traffic of that MVPN, and (c) none of the other PEs that
have VRFs of that MVPN use RSVP-TE P2MP LSP for that MVPN, then the
local PE SHOULD NOT originate an Intra-AS I-PMSI A-D route.
When BGP is used to exchange C-multicast routes, if it is known a
priori that as a matter of policy none of the MVPN sites connected to
a given PE can receive multicast traffic from other sites of that
MVPN (in other words, all these sites are only in the Sender Sites
set), and the PE uses ingress replication for that MVPN, then the PE
SHOULD NOT originate an Intra-AS I-PMSI A-D route for that MVPN.
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9.1.2. Receiving Intra-AS I-PMSI A-D routes
When a PE receives a BGP Update message that carries an Intra-AS I-
PMSI A-D route such that (a) at least one of the Route Targets of the
route matches one of the import Route Targets configured for a
particular VRF on the local PE, (b) either the route was originated
by some other PE within the same AS as the local PE, or the MVPN
associated with the VRF uses non-segmented inter-AS tunnels, and (c)
the BGP route selection determines that this is the best route with
respect to the NLRI carried by the route, the PE performs the
following.
If the route does not carry the PMSI Tunnel Attribute and ingress
replication is not used, either a) the PE that originated the route
will be using only S-PMSIs to send traffic to remote PEs, or b) as a
matter of policy, the PE that originated the route, cannot send
multicast traffic from the MVPN sites connected to it to other sites
of that MVPN (in other words, the sites connected to the PE are only
in the Receiver Sites set).
When BGP is used to exchange C-multicast routes, to distinguish
between cases (a) and (b) we use the presence/absence of the VRF
Route Import extended community in the unicast VPN routes, as
follows. As specified in section "VRF Route Import Extended
Community", if it is know a priori that none of the addresses carried
in the NLRI of a given (unicast) VPN route could act as multicast
sources and/or C-RP, then such a route does not carry the VRF Route
Import extended community. Hence based on the UMH selection algorithm
specified in [MVPN], such a route will be ineligible for the UMH
selection. This implies that if a given VPN route is selected by the
UMH selection procedures, and the PE that originates this VPN route
also originates an Intra-AS I-PMSI A-D route, but this route does not
carry the PMSI Tunnel attribute, then this PE will be using only S-
PMSIs for sending (multicast) data.
If the route carries the PMSI Tunnel attribute then:
+ If the Tunnel Type in the PMSI Tunnel attribute is set to Ingress
Replication, then the MPLS label and the address carried in the
Tunnel Identifier field of the PMSI Tunnel attribute should be
used when the local PE sends multicast traffic to the PE that
originated the route.
+ If the Tunnel Type in the PMSI Tunnel attribute is set to mLDP
P2MP LSP, or mLDP MP2MP LSP, or PIM-SSM tree, or PIM-SM tree, or
PIM-Bidir tree, the PE SHOULD join as soon as possible the P-
Multicast tree whose identity is carried in the Tunnel
Identifier.
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+ If the Tunnel Type in the PMSI Tunnel attribute is set to RSVP-TE
P2MP LSP, then the PE that originated the route MUST establish an
RSVP-TE P2MP LSP with the local PE as a leaf. This LSP may have
been established before the local PE receives the route, or may
be established after the local PE receives the route.
+ The receiving PE has to establish the appropriate state to
properly handle the traffic received on the P-Multicast tree.
+ If the PMSI Tunnel attribute does not carry a label, then all
packets that are received on the P-Multicast tree, as identified
by the PMSI Tunnel attribute, are forwarded using the VRFs that
has at least one of its import Route Targets that matches one of
the Route Targets of the received Intra-AS I-PMSI A-D route.
+ If the PMSI Tunnel attribute has the Tunnel Type set to mLDP P2MP
LSP, or PIM-SSM tree, or PIM-SM tree, or PIM-Bidir tree, or RSVP-
TE P2MP LSP, and the attribute also carries an MPLS label, then
this is an upstream assigned label, and all packets that are
received on the P-Multicast tree, as identified by the PMSI
Tunnel attribute, with that upstream assigned label are forwarded
using the VRFs that has at least one of its import Route Target
that matches one of the Route Targets of the received Intra-AS I-
PMSI A-D route.
Irrespective of whether the route carries the PMSI Tunnel attribute,
if the local PE uses RSVP-TE P2MP LSP for sending (multicast) traffic
from the VRF to the sites attached to other PEs, then the local PE
uses the Originating Router's IP address information carried in the
route to add the PE that originated the route as a leaf node to the
LSP.
9.2. MVPN Auto-Discovery/Binding - Inter-AS Operations
This section applies only to the case where segmented inter-AS
tunnels are used.
An Autonomous System Border Router (ASBR) may be configured to
support a particular MVPN as follows:
+ An ASBR MUST be be configured with a set of (import) Route
Targets (RTs) that specifies the set of MVPNs supported by the
ASBR. These Route Targets control acceptance of Intra-AS/Inter-AS
I-PMSI A-D routes by the ASBR. As long as unicast and multicast
connectivity are congruent, this could be the same set of Route
Targets as the one used for supporting unicast (and therefore
would not require any additional configuration above and beyond
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of what is required for unicast). Note that instead of being
configured, the ASBR MAY obtain this set of (import) Route
Targets (RTs) by using Route Target Constrain [RT-CONSTRAIN].
+ The ASBR MUST be (auto-)configured with an import Route Target
called "ASBR Import RT". ASBR Import RT controls acceptance of
Leaf A-D routes and C-multicast routes by the ASBR, and is used
to constrain distribution of both Leaf A-D routes and C-multicast
routes (see Section "Exchange of C-Multicast Routing Information
among PEs").
ASBR Import RT is an IP address specific Route Target. The Global
Administrator field of the ASBR Import RT MUST be set to the IP
address carried in the Next Hop of all the Inter-AS I-PMSI A-D
routes and S-PMSI A-D routes advertised by this ASBR (if the ASBR
uses different Next Hops, then the ASBR MUST be (auto-)configured
with multiple ASBR Import RTs, one per each such Next Hop). The
Local Administrator field of the ASBR Import RT MUST be set to 0.
If the ASBR supports Route Target Constrain [RT-CONSTRAIN], the
ASBR SHOULD advertise its ASBR Import RT within its own AS using
Route Target Constrains. To constrain distribution of the Route
Target Constrain routes to the AS of the advertising ASBR these
routes SHOULD carry the NO_EXPORT Community ([RFC1997]).
+ The ASBR MUST be configured with the tunnel types for the intra-
AS segments of the MVPNs supported by the ASBR, as well as
(depending on the tunnel type) the information needed to create
the PMSI attribute for these tunnel types. Note that instead of
being configured, the ASBR MAY derive the tunnel types from the
Intra-AS I-PMSI A-D routes received by the ASBR.
+ If the ASBR originates an Inter-AS I-PMSI A-D route for a
particular MVPN present on some of the PEs within its own AS, the
ASBR MUST be (auto-)configured with an RD for that MVPN. It is
RECOMMENDED that one of the following two options be used:
(1) To allow more aggregation of Inter-AS I-PMSI A-D routes it is
recommended that all the ASBRs within an AS that are configured
to originate an Inter-AS I-PMSI A-D route for a particular MVPN
be configured with the same RD (although for a given MVPN each AS
may assign this RD on its own, without coordination with other
ASes).
(2) To allow more control over spreading MVPN traffic among
multiple ASBRs within a given AS it is recommended for each ASBR
to have a distinct RD per each MVPN, in which case such an RD
SHOULD be auto-configured.
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If an ASBR is configured to support a particular MVPN, the ASBR MUST
participate in the intra-AS MVPN auto-discovery/binding procedures
for that MVPN within the ASBR's own AS, as specified in Section "MVPN
Auto-Discovery/Binding - Intra-AS Operations".
Moreover, in addition to the above the ASBR performs procedures
described in Sections "Originating Inter-AS I-PMSI A-D routes", "When
not to originate Inter-AS I-PMSI A-D routes", and "Propagating Inter-
AS I-PMSI A-D routes".
9.2.1. Originating Inter-AS I-PMSI A-D routes
For a given MVPN configured on an ASBR when the ASBR determines
(using the intra-AS auto-discovery procedures) that at least one of
the PEs of its own AS has (directly) connected site(s) of the MVPN,
the ASBR originates an Inter-AS I-PMSI A-D route and advertises it in
EBGP. The route is constructed as follows:
+ The route carries a single MCAST-VPN NLRI with the RD set to the
RD configured for that MVPN on the ASBR, and the Source AS set to
the Autonomous System number of the ASBR.
+ The route carries the PMSI Tunnel attribute if and only if an I-
PMSI is used for the MVPN. The Tunnel Type in the attribute is
set to Ingress Replication; the Leaf Information Required flag is
set to 1; the the attribute carries no MPLS labels.
+ The Next Hop field of the MP_REACH_NLRI attribute is set to a
routable IP address of the ASBR.
+ The default policy for aggregation of Intra-AS I-PMSI A-D routes
into an Inter-AS I-PMSI A-D route is that a given Inter-AS I-PMSI
A-D route aggregates only the Intra-AS I-PMSI A-D routes that
carry exactly the same set of RTs (note that this set may have
just one RT). In this case an Inter-AS I-PMSI A-D route
originated by an ASBR carries exactly the same RT(s) as the RT(s)
carried by the Intra-AS I-PMSI A-D routes that the ASBR
aggregates into that Inter-AS I-PMSI A-D route. An implementation
MUST support the default policy for aggregation of Intra-AS I-
PMSI A-D routes into an Inter-AS I-PMSI A-D route.
+ The default policy for aggregation could be modified via
configuration on the ASBR. An implementation MAY support such
functionality. Modified policy MUST include rules for
constructing RTs carried by the Inter-AS I-PMSI A-D routes
originated by the ASBR.
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An Inter-AS I-PMSI A-D route for a given <AS, MVPN> indicates
presence of the MVPN sites connected to one or more PEs of the AS.
An Inter-AS I-PMSI A-D route originated by an ASBR aggregates Intra-
AS I-PMSI A-D routes originated within the ASBR's own AS. Thus while
the Intra-AS I-PMSI A-D routes originated within an AS are at the
granularity of <PE, MVPN> within that AS, outside of that AS the
(aggregated) Inter-AS I-PMSI A-D routes could be at the granularity
of <AS, MVPN>.
9.2.2. When not to originate Inter-AS I-PMSI A-D routes
If for a given MVPN and a given AS all of its sites connected to the
PEs within the AS known a priori to have no multicast sources, then
ASBRs of that AS MAY refrain from originating an Inter-AS I-PMSI A-D
route for that MVPN at all.
9.2.3. Propagating Inter-AS I-PMSI A-D routes
An Inter-AS I-PMSI A-D route for a given MVPN originated by an ASBR
within a given AS is propagated via BGP to other ASes.
9.2.3.1. Propagating Inter-AS I-PMSI A-D routes - Overview
Suppose that an ASBR A installs an Inter-AS I-PMSI A-D route for MVPN
V that originated at a particular AS, AS1. The BGP next hop of that
route becomes A's "upstream multicast hop" on a multicast
distribution tree for V that is rooted at AS1. When the Inter-AS I-
PMSI A-D routes have been distributed to all the necessary ASes, they
define a "reverse path" from any AS that supports MVPN V back to AS1.
For instance, if AS2 supports MVPN V, then there will be a reverse
path for MVPN V from AS2 to AS1. This path is a sequence of ASBRs,
the first of which is in AS2, and the last of which is in AS1. Each
ASBR in the sequence is the BGP next hop of the previous ASBR in the
sequence on the given Inter-AS I-PMSI A-D route.
This reverse path information can be used to construct a
unidirectional multicast distribution tree for MVPN V, containing all
the ASes that support V, and having AS1 at the root. We call such a
tree an "inter-AS tree". Multicast data originating in MVPN sites
connected to PEs within a given AS will travel downstream along the
tree which is rooted at that AS.
The path along an inter-AS tree is a sequence of ASBRs; it is still
necessary to specify how the multicast data gets from a given ASBR to
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the set of ASBRs which are immediately downstream of the given ASBR
along the tree. This is done by creating "segments": ASBRs in
adjacent ASes will be connected by inter-AS segments, ASBRs in the
same AS will be connected by "intra-AS segments".
An ASBR initiates creation of an intra-AS segment when the ASBR
receives an Inter-AS I-PMSI A-D route from an EBGP neighbor.
Creation of the segment is completed as a result of distributing via
IBGP this route within the ASBR's own AS.
For a given inter-AS tunnel each of its intra-AS segments could be
constructed by its own independent mechanism. Moreover, by using
upstream assigned labels within a given AS multiple intra-AS segments
of different inter-AS tunnels of either the same or different MVPNs
may share the same P-Multicast tree.
If the P-Multicast tree that serves as a particular intra-AS segment
of an inter-AS tunnel is created by a multicast control protocol that
uses receiver-initiated joins (e.g, mLDP, any PIM variant), and this
P-Multicast tree does not aggregate multiple segments, then all the
information needed to create that segment is present in the PMSI
Tunnel attribute of the Inter-AS I-PMSI A-D routes. But if the P-
Multicast tree that serves as the segment is created by a protocol
that does not use receiver-initiated joins (e.g., RSVP-TE, ingress
unicast replication), or if this P-Multicast tree aggregates multiple
segments (irrespective of the multicast control protocol used to
create the tree), then it is also necessary to use Leaf A-D routes.
The precise conditions under which Leaf A-D routes need to be used
are described in subsequent sections.
Since (aggregated) Inter-AS I-PMSI A-D routes could have granularity
of <AS, MVPN>, an MVPN that is present in N ASes could have total of
N inter-AS tunnels. Thus for a given MVPN the number of inter-AS
tunnels constituting the I-PMSIs is independent of the number of PEs
that have this MVPN.
The precise rules for distributing and processing the Inter-AS I-PMSI
A-D routes across ASes are given in the following sections.
9.2.3.2. Inter-AS I-PMSI A-D route received via EBGP
When an ASBR receives from one of its EBGP neighbors a BGP Update
message that carries an Inter-AS I-PMSI A-D route, if (a) at least
one of the Route Targets carried in the message matches one of the
import Route Targets configured on the ASBR, and (b) the ASBR
determines that the received route is the best route for its NLRI,
the ASBR re-advertises this route to other PEs and ASBRs within its
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own AS (handling of this route by other PEs and ASBRs is described in
Section "Inter-AS I-PMSI A-D route received via IBGP").
When re-advertising an Inter-AS I-PMSI A-D route the ASBR MUST set
the Next Hop field of the MP_REACH_NLRI attribute to a routable IP
address of the ASBR.
If the received Inter-AS I-PMSI A-D route carries the PMSI Tunnel
attribute, then depending on the technology used to instantiate the
intra-AS segment of the inter-AS tunnel the ASBR constructs the PMSI
Tunnel attribute of the re-advertised Inter-AS I-PMSI A-D route as
follows.
+ If the ASBR uses ingress replication for the intra-AS segment of
the inter-AS tunnel, the re-advertised route MUST carry the PMSI
Tunnel attribute with the Tunnel Type set to Ingress Replication,
but no MPLS labels.
+ If the ASBR uses a P-Multicast tree for the intra-AS segment of
the inter-AS tunnel, the PMSI Tunnel attribute MUST contain the
identity of the tree (note that the ASBR could create the
identity of the tree prior to the actual instantiation of the
tree). If in order to instantiate the tree the ASBR needs to know
the leaves of the tree, then the ASBR obtains this information
from the Leaf A-D routes received from other PEs/ASBRs in ASBR's
own AS (as described in Section "Leaf A-D route received via
IBGP") by setting the Leaf Information Required flag in the PMSI
Tunnel attribute to 1.
+ An ASBR that uses a P-Multicast tree as the intra-AS segment of
the inter-AS tunnel MAY aggregate two or more MVPNs present on
the ASBR onto the same tree. In this case in addition to the
identity of the tree, the PMSI Tunnel attribute MUST carry an
MPLS upstream-assigned label which the PE has bound uniquely to
the MVPN associated with this update (as determined by its RTs).
If the ASBR has already advertised Inter-AS I-PMSI A-D routes for
two or more MVPNs that it now desires to aggregate, then the ASBR
MUST re-advertise those routes. The re-advertised routes MUST be
the same as the original ones, except for the PMSI Tunnel
attribute and the MVPN label.
9.2.3.2.1. Originating Leaf A-D route into EBGP
In addition the ASBR MUST send to the EBGP neighbor from whom it
received the Inter-AS I-PMSI A-D route, a BGP Update message that
carries a Leaf A-D route constructed as follows.
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+ The route carries a single MCAST-VPN NLRI with the Route Key
field set to the MCAST-VPN NLRI of the Inter-AS I-PMSI A-D route
received from that neighbor and the Originating Router's IP
address set to the IP address of the ASBR (this MUST be a
routable IP address).
+ The Leaf A-D route MUST include the PMSI Tunnel attribute with
the Tunnel Type set to Ingress Replication, and the Tunnel
Identifier set to a routable address of the advertising router.
The PMSI Tunnel attribute MUST carry a downstream assigned MPLS
label that is used by the advertising router to demultiplex the
MVPN traffic received over a unicast tunnel from the EBGP
neighbor.
+ The ASBR constructs an IP-based Route Target extended community
by placing the IP address carried in the next hop of the received
Inter-AS I-PMSI A-D route in the Global Administrator field of
the community, with the Local Administrator field of this
community set to 0, and sets the Extended Communities attribute
of the Leaf A-D route to that community. Note that this Route
Target is the same as the ASBR Import RT of the EBGP neighbor
from which the ASBR received the Inter-AS I-PMSI A-D route.
+ The Next Hop field of the MP_REACH_NLRI attribute of the route
MUST be set to the same IP address as the one carried in the
Originating Router's IP Address field of the route.
+ To constrain the distribution scope of this route the route MUST
carry the NO_ADVERTISE BGP community ([RFC1997]).
Handling of this Leaf A-D route by the EBGP neighbor is described in
Section "Leaf A-D route received via EBGP".
The ASBR MUST set up its forwarding state such that packets that
arrive on the one-hop ASBR-ASBR LSP, as specified in the PMSI Tunnel
Attribute of the Leaf A-D route, are transmitted on the intra-AS
segment, as specified in the PMSI Tunnel Attribute of the inter-AS I-
PMSI A-D route that the ASBR re-advertises in its own AS. However,
the packets MAY be filtered before forwarding, as specified in
Section "Optimizing Bandwidth by IP filtering on ASBRs".
9.2.3.3. Leaf A-D route received via EBGP
When an ASBR receives via EBGP a Leaf A-D route originated by its
neighbor ASBR, if the Route Target carried in the Extended
Communities attribute of the route matches one of the ASBR Import RT
(auto)configured on the ASBR, the ASBR performs the following.
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The ASBR finds an Inter-AS I-PMSI A-D route whose MCAST-VPN NLRI has
the same value as the Route Key field of the the Leaf A-D route.
If the found Inter-AS I-PMSI A-D route was originated by ASBR itself,
then the ASBR sets up its forwarding state such that packets received
on the intra-AS tunnels originating in the ASBR's own AS are
transmitted on the one hop ASBR-ASBR LSP specified by the MPLS label
carried in the PMSI Tunnel attribute of the received Leaf A-D route.
(However the packets MAY be filtered before transmission as specified
in Section "Optimizing Bandwidth by IP filtering on ASBRs"). The
intra-AS tunnels are specified in the PMSI Tunnel attribute of all
the Intra-AS I-PMSI A-D routes received by the ASBR that the ASBR
aggregated into the Inter-AS I-PMSI A-D route. For each of these
intra-AS tunnels, if a non-zero MPLS label is carried in the PMSI
Tunnel attribute (i.e aggregation is used) then only packets received
on the inner LSP corresponding to that label MUST be forwarded, not
the packets received on the outer LSP, as the outer LSP possibly
carries the traffic of other VPNs.
If the found Inter-AS I-PMSI A-D route was originated by some other
ASBR, then the ASBR sets up its forwarding state such that packets
received on the intra-AS tunnel segment, as specified in the PMSI
Tunnel attribute of the found Inter-AS I-PMSI A-D route, are
transmitted on the one hop ASBR-ASBR LSP, as specified by the MPLS
label carried in the PMSI Tunnel attribute of the Leaf A-D route.
9.2.3.4. Inter-AS I-PMSI A-D route received via IBGP
In the context of this section we use the term "PE/ASBR router" to
denote either a PE or an ASBR router.
If a given Inter-AS I-PMSI A-D route is received via IBGP by a BGP
Route Reflector, the BGP Route Reflector MUST NOT modify the Next Hop
field of the MP_REACH_NLRI attribute when re-advertising the route
into IBGP (this is because the information carried in the Next Hop is
used for controling flow of C-multicast routes, as specified in
Section "Propagating C-multicast routes by an ASBR").
If a given Inter-AS I-PMSI A-D route is advertised within an AS by
multiple ASBRs of that AS, the BGP best route selection performed by
other PE/ASBR routers within the AS does not require all these
PE/ASBR routers to select the route advertised by the same ASBR - to
the contrary different PE/ASBR routers may select routes advertised
by different ASBRs.
When a PE/ASBR router receives from one of its IBGP neighbors a BGP
Update message that carries an Inter-AS I-PMSI A-D route, if (a) at
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least one of the Route Targets carried in the message matches one of
the import Route Targets configured on the PE/ASBR, and (b) the
PE/ASBR determines that the received route is the best route to the
destination carried in the NLRI of the route, the PE/ASBR performs
the following operations.
If the router is a PE, then the router imports the route into the
VRF(s) that have the matching import Route Targets.
If the router is an ASBR then the ASBR propagates the route to its
EBGP neighbors. When propagating the route to the EBGP neighbors the
ASBR MUST set the Next Hop field of the MP_REACH_NLRI attribute to a
routable IP address of the ASBR. If the received Inter-AS I-PMSI A-D
route carries the PMSI Tunnel attribute, then the propagated route
MUST carry the PMSI Tunnel attribute with the Tunnel Type set to
Ingress Replication; the attribute carries no MPLS labels.
If the received Inter-AS I-PMSI A-D route carries the PMSI Tunnel
attribute with the Tunnel Type set to mLDP P2MP LSP, or PIM-SSM tree,
or PIM-SM tree, or PIM-Bidir tree, the PE/ASBR SHOULD join as soon as
possible the P-Multicast tree whose identity is carried in the Tunnel
Identifier.
If the received Inter-AS I-PMSI A-D route carries the PMSI Tunnel
attribute with the Tunnel Identifier set to RSVP-TE P2MP LSP, then
the ASBR that originated the route MUST establish an RSVP-TE P2MP LSP
with the local PE/ASBR as a leaf. This LSP MAY have been established
before the local PE/ASBR receives the route, or MAY be established
after the local PE receives the route.
If the received Inter-AS I-PMSI A-D route carries the PMSI Tunnel
attribute with the Tunnel Type set to mLDP P2MP LSP, or RSVP-TE P2MP
LSP, or PIM-SSM, or PIM-SM tree, or PIM-Bidir tree, but the attribute
does not carry a label, then the P-Multicast tree, as identified by
the PMSI Tunnel Attribute, is an intra-AS LSP segment that is part of
the inter-AS Tunnel for the MVPN advertised by the Inter-AS I-PMSI A-
D route and rooted at the AS that originated the Inter-AS I-PMSI A-D
route. If the PMSI Tunnel attribute carries a (upstream assigned)
label, then a combination of this tree and the label identifies the
intra-AS segment. If the receiving router is an ASBR, this intra-AS
segment may further be stitched to the ASBR-ASBR inter-AS segment of
the inter-AS tunnel. If the PE/ASBR has local receivers in the MVPN,
packets received over the intra-AS segment must be forwarded to the
local receivers using the local VRF.
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9.2.3.4.1. Originating Leaf A-D route into IBGP
If the Leaf Information Required flag in the PMSI Tunnel attribute of
the received Inter-AS I-PMSI A-D route is set to 1, then the PE/ASBR
MUST originate a new Leaf A-D route as follows.
+ The route carries a single MCAST-VPN NLRI with the Route Key
field set to the MCAST-VPN NLRI of the Inter-AS I-PMSI A-D route
received from that neighbor, and the Originating Router's IP
address set to the IP address of the PE/ASBR (this MUST be a
routable IP address).
+ If the received Inter-AS I-PMSI A-D route carries the PMSI Tunnel
attribute with the Tunnel Type set to Ingress Replication, then
the Leaf A-D route MUST carry the PMSI Tunnel attribute with the
Tunnel Type set to Ingress Replication. The Tunnel Identifier
MUST carry a routable address of the PE/ASBR. The PMSI Tunnel
attribute MUST carry a downstream assigned MPLS label that is
used to demultiplex the MVPN traffic received over a unicast
tunnel by the PE/ASBR.
+ The PE/ASBR constructs an IP-based Route Target community by
placing the IP address carried in the next hop of the received
Inter-AS I-PMSI A-D route in the Global Administrator field of
the community, with the Local Administrator field of this
community set to 0, and sets the Extended Communities attribute
of the Leaf A-D route to that community.
+ The Next Hop field of the MP_REACH_NLRI attribute of the route
MUST be set to the same IP address as the one carried in the
Originating Router's IP Address field of the route.
+ To constrain the distribution scope of this route the route MUST
carry the NO_EXPORT BGP community ([RFC1997]).
+ Once the Leaf A-D route is constructed, the PE/ASBR advertises
this route into IBGP.
9.2.3.5. Leaf A-D route received via IBGP
When an ASBR receives via IBGP a Leaf A-D route, if the Route Target
carried in the Extended Communities attribute of the route matches
one of the ASBR Import RT (auto)configured on the ASBR, the ASBR
performs the following.
The ASBR finds an Inter-AS I-PMSI A-D route whose MCAST-VPN NLRI has
the same value as the Route Key field of the the Leaf A-D route.
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The received route may carry either (a) no PMSI Tunnel attribute, or
(b) the PMSI Tunnel attribute, but only with the Tunnel Type set to
Ingress Replication.
If the received route does not carry the PMSI Tunnel attribute, the
ASBR uses the information from the received route to determine the
leaves of the P-Multicast tree rooted at the ASBR that would be used
for the intra-AS segment associated with the found Inter-AS I-PMSI A-
D route. The IP address of a leaf is the IP address carried in the
Originating Router's IP address field of the received Leaf A-D route.
If the received route carries the PMSI Tunnel attribute with the
Tunnel Type set to Ingress Replication the ASBR uses the information
carried by the route to construct the intra-AS segment with ingress
replication.
9.2.3.6. Optimizing Bandwidth by IP filtering on ASBRs
An ASBR that has a given Inter-AS I-PMSI A-D route MAY discard some
of the traffic carried in the tunnel specified in the PMSI Tunnel
attribute of this route if the ASBR determines that there are no
downstream receivers for that traffic.
When BGP is being used to distribute C-multicast routes, an ASBR that
has a given Inter-AS I-PMSI A-D route MAY discard traffic from a
particular customer multicast source C-S and destined to a particular
customer multicast group address C-G that is carried over the tunnel
specified in the PMSI Tunnel attribute of the route, if none of the
C-multicast routes on the ASBR with RD and Source AS being the same
as the RD and Source AS of the Inter-AS I-PMSI A-D route matches the
(C-S,C-G) tuple. A C-multicast route is said to match a (C-S,C-G)
tuple, if it is a Source Tree Join route with Multicast Source set to
C-S and Multicast Group set to C-G, or a Shared Tree Join route with
Multicast Group set to C-G.
The above procedures MAY also apply to an ASBR that originates a
given Inter-AS I-PMSI A-D route. In this case the ASBR applies them
to the traffic carried over the tunnels specified in the PMSI Tunnel
attribute of the Intra-AS I-PMSI A-D routes that the ASBR aggregates
into the Inter-AS I-PMSI A-D route, and whose tails are stiched to
the one-hop ASBR-ASBR tunnel specified in the Inter-AS I-PMSI A-D
route.
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10. Non-congruent Unicast and Multicast Connectivity
It is possible to deploy MVPN such that the multicast routing and the
unicast routing are "non-congruent". For instance, the CEs may be
distributing to the PEs a special set of unicast routes that are to
be used exclusively for the purpose of upstream multicast hop
selection, and not used for unicast routing at all. (For example,
when BGP is the CE-PE unicast routing protocol, the CEs may be using
SAFI 2 ("Network Layer Reachability Information used for multicast
forwarding" [IANA-SAFI]), and either IPv4 or IPv6 AFI to distribute a
special set of routes that are to be used for, and only for, upstream
multicast hop selection.) In such a situation, we will speak of the
MVPN as having two VRFs on a given PE, one containing the routes that
are used for unicast, the other containing the unicast routes that
are used for upstream multicast hop (UMH) selection. We will call the
former the "unicast routing VRF", and the latter the "UMH VRF"
(upstream multicast hop VRF).
In this document, when we speak without qualification of the MVPN's
VRF, then if the MVPN has both a unicast VRF and a UMH VRF, we are
speaking of the UMH VRF. (Of course, if there is no separate UMH VRF,
then we are speaking of the unicast VRF.)
If there is a separate UMH VRF, it MAY have its own import and export
Route Targets, different from the ones used by the unicast VRF. These
Route Targets MUST be used to control distribution of auto-discovery
routes. In addition, the export Route Targets of the UMH VRF are
added to the Route Targets used by the unicast VRF when originating
(unicast) VPN-IP routes. The import Route Targets associated with a
given UMH VRF are used to determine which of the received (unicast)
VPN-IP routes should be accepted into the UMH VRF.
If a PE maintains an UMH VRF for that MVPN, then it is RECOMMENDED
that the UMH VRF should use the same RD as the one used by the
unicast VRF of that MVPN.
If an MVPN site is multi-homed to several PEs, then to support non-
congruent unicast and multicast connectivity, on each of these PEs
the UMH VRF of the MVPN MUST use its own distinct RD (although on a
given PE the RD used by the UMH VRF SHOULD be the same as the one
used by the unicast VRF).
If an MVPN has a UMH VRF distinct from its unicast VRF, then one
option to support non-congruency is by exchanging the routes from/to
that UMH VRF by using the same AFI/SAFI as used by the routes from
the unicast VRF.
Another option is to exchange the routes from/to the UMH VRF using
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the IPv4 or IPv6 AFI (as appropriate), but with the SAFI set to
"Multicast for BGP/MPLS IP Virtual Private Networks (VPNs)" [IANA-
SAFI]. The NLRI carried by these routes is defined as follows:
+---------------------------+
| Length (1 octet) |
+---------------------------+
| Prefix (variable) |
+---------------------------+
The use and the meaning of these fields are as follows:
a) Length:
The Length field indicates the length in bits of the address
prefix plus the label(s).
b) Prefix:
The Prefix field contains a Route Distinguisher as defined
in [RFC4364] prepended to an IPv4 or IPv6 address prefix,
followed by enough trailing bits to make the end of the
field fall on an octet boundary. Note that the value of
trailing bits is irrelevant.
These routes MUST carry the VRF Route Import Extended Community. If
for a given MVPN BGP is used for exchanging C-multicast routes, or if
segmented inter-AS tunnels are used, then these routes also MUST
carry the Source AS extended community.
The detailed procedures for selecting forwarder PE in the presence of
such routes are outside the scope of this document. However, this
document requires these procedures to preserve the constrains imposed
by the single forwarder PE selection procedures, as specified in
[MVPN].
11. Exchange of C-Multicast Routing Information among PEs
VPN C-Multicast Routing Information is exchanged among PEs by using
C-multicast routes that are carried using MCAST-VPN NLRI. These
routes are originated and propagated as follows.
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11.1. Originating C-multicast routes by a PE
Part of the procedures for constructing MCAST-VPN NLRI depend on the
multicast routing protocol between CE and PE (C-multicast protocol).
11.1.1. Originating routes: PIM as the C-Multicast protocol
The following specifies construction of MCAST-VPN NLRI of C-multicast
routes for the case where the C-multicast protocol is PIM. These C-
multicast routes are originated as a result of updates in (C-S, C-G),
or (C-*, C-G) state learnt by a PE via the C-multicast protocol.
Note that creation and deletion of (C-S, C-G, RPTbit) states on a PE
when the C-multicast protocol is PIM do not result in any BGP
actions.
11.1.1.1. Originating Source Tree Join C-multicast route
Whenever (a) a C-PIM instance on a particular PE creates a new (C-
S,C-G) state, and (b) the selected upstream PE for C-S (see [MVPN])
is not the local PE, then the local PE MUST originate a a C-multicast
route of a type Source Tree Join. The Multicast Source field in the
MCAST-VPN NLRI of the route is set to C-S, the Multicast Group field
is set of C-G.
This C-multicast route is said to "correspond" to the C-PIM (C-S,C-G)
state.
The semantics of the route is that the PE has one or more receivers
for (C-S, C-G) in the sites connected to the PE (the route has the
(C-S, C-G) Join semantics).
Whenever a C-PIM instance on a particular PE deletes a (C-S,C-G)
state, the corresponding C-multicast route MUST be withdrawn. (The
withdrawal of the route has the (C-S, C-G) Prune semantics). The
MCAST-VPN NLRI of the withdrawn route is carried in the
MP_UNREACH_NLRI attribute.
11.1.1.2. Originating Shared Tree Join C-multicast route
Whenever (a) a C-PIM instance on a particular PE creates a new
(C-*,C-G) state, and (b) the selected upstream PE for the C-RP
corresponding to the C-G (see [MVPN]) is not the local PE, then the
local PE MUST originate a a C-multicast route of a type Shared Tree
Join. The Multicast Source field in the MCAST-VPN NLRI of the route
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is set to the C-RP address. The Multicast Group field in the MCAST-
VPN NLRI is set to the C-G address.
This C-multicast route is said to "correspond" to the C-PIM (C-*,C-G)
state.
The semantics of the route is that the PE has one or more receivers
for (C-*, C-G) in the sites connected to the PE (the route has the
(C-*, C-G) Join semantics).
Whenever a C-PIM instance on a particular PE deletes a (C-*,C-G)
state, the corresponding C-multicast route MUST be withdrawn. (The
withdrawal of the route has the (C-S, C-G) Prune semantics). The
MCAST-VPN NLRI of the withdrawn route is carried in the
MP_UNREACH_NLRI attribute.
11.1.2. Originating routes: mLDP as the C-Multicast protocol
The following specifies construction of MCAST-VPN NLRI of C-multicast
routes for the case where the C-multicast protocol is mLDP [mLDP].
Whenever a PE receives from one of its CEs a P2MP Label Map <X, Y, L>
over interface I, where X is the Root Node Address, Y is the Opaque
Value, and L is an MPLS label, the PE checks whether it already has
state for <X, Y> in the VRF associated with the CE. If yes, then all
the PE needs to do in this case is to update its forwarding state by
adding <I, L> to the forwarding state associated with <X, Y>.
If the PE does not have state for <X, Y> in the VRF associated with
the CE, then the PE constructs a Source Tree Join C-multicast route
whose MCAST-VPN NLRI contains X as the Multicast Source field, and Y
as the Multicast Group field.
Whenever a PE deletes a previously created <X, Y> state that had
resulted in originating a C-multicast route, the PE withdraws the C-
multicast route. The MCAST-VPN NLRI of the withdrawn route is carried
in the MP_UNREACH_NLRI attribute.
11.1.3. Constructing the rest of the C-multicast route
The rest of the C-multicast route is constructed as follows (the same
procedures apply to both PIM and mLDP as the C-Multicast protocol).
The local PE executes the procedures of [MVPN] to find the selected
Upstream Multicast Hop (UMH) route and the selected upstream PE for
the address carries in the Multicast Source field of MCAST-VPN NLRI.
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From the selected UMH route the local PE extracts (a) the autonomous
system number of the upstream PE (as carried in the Source AS
extended community of the route), and (b) the C-multicast Import RT
of the VRF on the upstream PE (the value of this C-multicast Import
RT is the value of the VRF Route Import Extended Community carried by
the route). The Source AS field in the C-multicast route is set to
that autonomous system. The Route Target Extended Community of the C-
multicast route is set to that C-multicast Import RT.
If there is more than one (remote) PE that originates the (unicast)
route to the address carried in the Multicast Source field of the
MCAST-VPN NLRI, then the procedures for selecting the UMH route and
the upstream PE to reach that address are as specified in [MVPN].
If the local and the upstream PEs are in the same AS, then the RD of
the advertised MCAST-VPN NLRI is set to the RD of the VPN-IP route
that contains the address carried in the Multicast Source field.
The C-multicast route is then advertised into IBGP.
If the local and the upstream PEs are in different ASes, then the
local PE finds in its VRF an Inter-AS I-PMSI A-D route whose Source
AS field carries the autonomous system number of the upstream PE.
The RD of the found Inter-AS I-PMSI A-D route is used as the RD of
the advertised C-multicast route. The local PE constructs an IP-based
Route Target community by placing the next hop of the found Inter-AS
I-PMSI A-D route in the Global Administrator field of this community,
with the Local Administrator field of this community set to 0, and
adds this community to the Extended Communities attribute of the C-
multicast route. (Note that this Route Target is the same as the ASBR
Import RT of the ASBR identified by the next hop of the found Inter-
AS I-PMSI A-D route.)
Inter-AS I-PMSI A-D routes are not used to support non-segmented
inter-AS tunnels. To support non-segmented inter-AS tunnels, if the
local and the upstream PEs are in different ASes, the local system
finds in its VRF an Intra-AS I-PMSI A-D route from the upstream PE
(the Originating Router's IP Address field of that route has the same
value as the one carried in the VRF Route Import of the (unicast)
route to the address carried in the Multicast Source field). The RD
of the found Intra-AS I-PMSI A-D route is used as the RD of the
advertised C-multicast route. The Source AS field in the C-multicast
route is set to value of the Originating Router's IP Address field of
the found Intra-AS I-PMSI A-D route.
The Next Hop field of the MP_REACH_NLRI attribute MUST be set to a
routable IP address of the local PE.
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If the next hop of the found (Inter-AS or Intra-AS) I-PMSI A-D route
is an EBGP neighbor of the local PE, then the PE advertises the C-
multicast route to that neighbor. If the next hop of the found
(Inter-AS or Intra-AS) I-PMSI A-D route is within the same AS as the
local PE, then the PE advertises the C-multicast route into IBGP.
11.1.4. Unicast Route Changes
The particular UMH route that is selected by a given PE for a given
C-S may be influenced by the network's unicast routing. In that case,
a change in the unicast routing may invalidate prior choices of the
UMH route for some C-S. If this happens, the local PE MUST execute
the UMH route selection procedures for C-S again. If the result is
that a different UMH route is selected, then for all C-G, any
previously originated C-multicast routes for (C-S,C-G) MUST be re-
originated.
Similarly, if a unicast routing change results in a change of the UMH
route for a C-RP, then for all C-G such that C-RP is the RP
associated with C-G, any previously originated C-multicast routes for
(C-*,C-G) MUST be re-originated.
11.2. Propagating C-multicast routes by an ASBR
When an ASBR receives a BGP Update message that carries a C-multicast
route, if at least one of the Route Targets of the route matches one
of the ASBR Import RTs (auto)configured on the ASBR, the ASBR finds
an Inter-AS I-PMSI A-D route whose RD and Source AS matches the RD
and Source AS carried in the C-multicast route. If no matching route
is found, the ASBR takes no further actions. If a matching route is
found, the ASBR proceeds as follows.
To support non-segmented inter-AS tunnels, instead of matching the RD
and Source AS carried in the C-multicast route against the RD and
Source AS of an Inter-AS I-PMSI A-D route, the ASBR should match it
against the RD and the Originating Router's IP Addr of the Intra-AS
I-PMSI A-D routes.
The ASBR first checks if it already has one or more C-multicast
routes that have the same MCAST-VPN NLRI as the newly received route.
If such route(s) already exists, the ASBR keeps the newly received
route, but SHALL NOT re-advertise the newly received route.
Otherwise, the ASBR re-advertises the route, as described further
down.
When an ASBR receives a BGP Update message that carries a withdraw of
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a previously advertised C-multicast route, the ASBR first checks if
it already has at least one other C-multicast route that has the same
MCAST-VPN NLRI. If such a route already exists, the ASBR processes
the withdrawn route, but SHALL NOT re-advertise the withdraw.
Otherwise, the ASBR re-advertises the withdrawal of the previously
advertised C-multicast route, as described below.
If the ASBR is the ASBR that originated the found Inter-AS I-PMSI A-D
route, then before re-advertising the C-multicast route into IBGP the
ASBR removes from the route the Route Target that matches one of the
ASBR Import RTs (auto)configured on the ASBR.
If the ASBR is not the ASBR that originated the found Inter-AS I-PMSI
A-D route, then before re-advertising the C-multicast route, the ASBR
modifies the Extended Communities attribute of the C-multicast route
by replacing the Route Target of the route that matches one of the
ASBR Import RTs (auto)configured on the ASBR with a new Route Target
constructed as follows. The new Route Target is an IP-based Route
Target that has the Global Administrator field set to the Next Hop of
the found Inter-AS I-PMSI A-D route, and Local Administrator field of
this community set to 0. Note that this newly constructed Route
Target is the same as the ASBR Import RT of the ASBR identified by
the next hop of the found Inter-AS I-PMSI A-D route. The rest of the
Extended Communities attribute of the route SHOULD be passed
unmodified.
The Next Hop field of the MP_REACH_NLRI attribute SHOULD be set to an
IP address of the ASBR.
If the Next Hop field of the MP_REACH_NLRI of the found (Inter-AS or
Intra-AS) I-PMSI A-D route is an EBGP neighbor of the ASBR, then the
ASBR re-advertises the C-multicast route to that neighbor. If the
Next Hop field of the MP_REACH_NLRI of the found (Inter-AS or Intra-
AS) I-PMSI A-D route is an IBGP neighbor of the ASBR, the ASBR re-
advertises the C-multicast route into IBGP. If it is the ASBR that
originated the found Inter-AS I-PMSI A-D route in the first place,
then the ASBR just re-advertises the C-multicast route into IBGP.
11.3. Receiving C-multicast routes by a PE
When a PE receives a C-multicast route the PE checks if any of the
Route Target communities carried in the Extended Communities
attribute of the route match any of the C-multicast Import RTs
associated with the VRFs of any MVPN maintained by the PE. If no
match is found the PE SHOULD discard the route. Otherwise, (if a
match is found), the PE checks if the address carried in the
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Multicast Source field of the C-multicast route matches one of the
(unicast) VPN-IP routes advertised by PE from the VRF. If no match is
found the PE SHOULD discard the route. Otherwise, (if a match is
found), the PE proceeds as follows, depending on the multicast
routing protocol between CE and PE (C-multicast protocol).
11.3.1. Receiving routes: PIM as the C-Multicast protocol
The following described procedures when PIM is used as the multicast
routing protocol between CE and PE (C-multicast protocol).
Since C-multicast routing information is disseminated by BGP, PIM
messages are never sent from one PE to another.
11.3.1.1. Receiving Source Tree Join C-multicast route
If the received route has the route type set to Source Tree Join,
then the PE creates a new (C-S, C-G) state in its MVPN-TIB from the
Multicast Source and Multicast Group fields in the MCAST-VPN NLRI of
the route, if such a state does not already exist.
If the local policy on the PE is to bind (C-S, C-G) to an S-PMSI,
then the PE adds the S-PMSI to the outgoing interface list of the (C-
S, C-G) state, if it is not already there. Otherwise, the PE adds an
I-PMSI to the outgoing interface list of the (C-S, C-G) state, if it
is not already there.
When, for a said VRF, the last Source Tree Join C-multicast route for
(C-S, C-G) is withdrawn, resulting in the situation where the VRF
contains no Source Tree Join C-multicast route for (C-S, C-G) the PE
MUST remove the I-PMSI/S-PMSI from the outgoing interface list of the
(C-S, C-G) state. Depending on the (C-S, C-G) state of the PE-CE
interfaces, this may result in the PE using PIM procedures to prune
itself off the (C-S, C-G) tree. If C-G is not in the SSM range for
the VRF, then removing the I-PMSI/S-PMSI from the outgoing interface
list of the (C-S, C-G) state SHOULD be done after a delay that is
controlled by a timer. The value of the timer MUST be configurable.
The purpose of this timer is to ensure that the PE does not stop
forwarding (C-S, C-G) onto a PMSI tunnel until all the PEs of the
same MVPN have had time to receive the withdrawal of the Source
Active A-D route for (C-S, C-G) (see Section 13.1 "Source Within a
Site - Source Active Advertisement"), and the PE connected to C-RP
starts forwarding (C-S, C-G) on the C-RPT.
Note that before the PE stops forwarding (C-S, C-G), there is a
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possibility to have (C-S, C-G) packets being sent at the same time on
the PMSI by both the local PE and the PE connected to the site that
contains C-RP. This would result in a transient unnecessary traffic
on the provider backbone. However, no duplicates will reach customer
hosts subscribed to C-G as long as the downstream PEs apply
procedures described in section 9.1 of [MVPN].
11.3.1.2. Receiving Shared Tree Join C-multicast route
If the received route has the route type set to Shared Tree Join,
then the PE creates a new (C-*, C-G) state in its MVPN-TIB with the
RP address for that state taken from the Multicast Source, and C-G
for that state taken from the Multicast Group fields of the MCAST-VPN
NLRI of the route, if such a state does not already exist. If there
is no S-PMSI for (C-*, C-G), then the PE adds I-PMSI to the outgoing
interface list of the state if it is not already there. If there is
an S-PMSI for (C-*, C-G), then the PE adds S-PMSI to the outgoing
interface list of the state if it is not already there.
When, for a said VRF, the last Shared Tree Join C-multicast route for
(C-*, C-G) is withdrawn, resulting in the situation where the VRF
contains no Shared Tree Join C-multicast route for (C-*, C-G) the PE
MUST remove the I-PMSI/S-PMSI from the outgoing interface list of the
(C-*, C-G) state. Depending on the (C-*, C-G) state of the PE-CE
interfaces, this may result in the PE using PIM procedures to prune
itself off the (C-*, C-G) tree.
11.3.2. Receiving routes: mLDP as the C-Multicast protocol
The following described procedures when mLDP is used as the multicast
routing protocol between CE and PE (C-multicast protocol).
When mLDP is used as a C-multicast protocol, the only valid type of a
C-multicast route that a PE could receive is a Source Tree Join C-
multicast route.
When the PE receives a Source Tree Join C-multicast route, the PE
applies, in the scope of this VRF, the P2MP mLDP procedures for a
transit node using the value carried in the Multicast Source field of
the route as the C-Root Node Identifier, and the value carried in the
Multicast Group of the route as the C-LDP MP Opaque Value Element.
If there is no S-PMSI for <C-Root Node Identifier, C-LDP MP Opaque
Value Element> then the PE creates and advertises an S-PMSI as
described in Section "Using S-PMSI A-D routes to Bind C-trees to P-
tunnels" using C-Root Node Identifier as the value for the Multicast
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Source field of the S-PMSI A-D route and C-LDP MP Opaque Value
Element as the value for the Multicast Group field of the route.
To improve scalability when mLDP is used as the C-Multicast protocol
for a given MVPN, within each AS that has sites of that MVPN
connected to the PEs of that AS, all the S-PMSIs of that MVPN MAY be
aggregated into a single P-Multicast tree (by using upstream assigned
labels).
11.4. C-multicast routes aggregation
Note that C-multicast routes are "de facto" aggregated by BGP. This
is because the MCAST-VPN NLRIs advertised by multiple PEs, for a C-
multicast route for a particular C-S and C-G (or a particular C-* and
C-G) of a given MVPN are identical.
Hence a BGP Route Reflector or ASBR that receives multiple such
routes with the same NLRI will re-advertise only one of these routes
to other BGP speakers.
This implies that C-multicast routes for a given (S,G) of a given
MVPN originated by PEs that are clients of a given Route Reflector
are aggregated by the Route Reflector. For instance, if multiple PEs
that are clients of a Route Reflector, have receivers for a specific
SSM channel of a MVPN, they will all advertise an identical NLRI for
the "Source Tree Join" C-multicast route. However only one C-
multicast route will be advertised by the Route Reflector for this
specific SSM channel of that MVPN, to other PEs and Route Reflectors
that are clients of the Route Reflector.
This also implies that an ASBR aggregates all the received C-
multicast routes for a given (S,G) (or a given (*,G)) of a given MVPN
into a single C-multicast route.
To further reduce the routing churn due to C-multicast routes changes
a Route Reflector that re-advertises a C-multicast route SHOULD set
the Next Hop field of the MP_REACH_NLRI attribute of the route to an
IP address of the Route Reflector. Likewise, an ASBR that re-
advertises a C-multicast route SHOULD set the Next Hop field of the
MP_REACH_NLRI attribute of the route to an IP address of the ASBR.
Further a BGP receiver, that receives multiple such routes with the
same NLRI for the same C-multicast route, will potentially create
forwarding state based on a single C-multicast route. As per the
procedures described in Section "Receiving C-Multicast Routes by a
PE", this forwarding state will be the same as the state that would
have been created based on another route with same NLRI.
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12. Using S-PMSI A-D routes to Bind C-trees to P-tunnels
This section describes BGP-based procedures for using S-PMSIs A-D
routes to bind (C-S, C-G) trees to P-tunnels.
12.1. Originating S-PMSI A-D routes
The following describes procedures for originating S-PMSI A-D routes
by a PE.
The PE constructs the MCAST-VPN NLRI of an S-PMSI A-D route for a
given (C-S, C-G) as follows.
+ The RD in this NLRI is set to the RD of the MVPN's VRF associated
with (C-S, C-G).
+ The Multicast Source field MUST contain the source address
associated with the C-multicast stream, and the Multicast Source
Length field is set appropriately to reflect this.
+ The Multicast Group field MUST contain the group address
associated with the C-multicast stream, and the Multicast Group
Length field is set appropriately to reflect this.
+ The Originating Router's IP Address field MUST be set to the IP
address that the (local) PE places in the Global Administrator
field of the VRF Route Import extended community of the VPN-IP
routes advertised by the PE. Note that the <RD, Originating
Router's IP address> tuple uniquely identifies a given multicast
VRF.
The PE constructs the rest of the S-PMSI A-D route as follows.
Depending on the type of a P-Multicast tree used for the P-tunnel,
the PMSI tunnel attribute of the S-PMSI A-D route is constructed as
follows:
+ The PMSI tunnel attribute MUST contain the identity of the P-
Multicast tree (note that the PE could create the identity of the
tree prior to the actual instantiation of the tree).
+ If in order to establish the P-Multicast tree the PE needs to
know the leaves of the tree within its own AS, then the PE
obtains this information from the Leaf A-D routes received from
other PEs/ASBRs within its own AS (as other PEs/ASBRs originate
Leaf A-D routes in response to receiving the S-PMSI A-D route) by
setting the Leaf Information Required flag in the PMSI Tunnel
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attribute to 1.
+ If a PE originates S-PMSI A-D routes with the Leaf Information
Required flag in the PMSI Tunnel attribute set to 1, then the PE
MUST be (auto)configured with an import Route Target, which
controls acceptance of Leaf A-D routes by the PE. (Procedures for
originating Leaf A-D routes by the PEs that receive the S-PMSI A-
D route are described in section "Receiving S-PMSI A-D routes by
PEs.)
This Route Target is IP address specific. The Global
Administrator field of this Route Target MUST be set to the IP
address carried in the Next Hop of all the S-PMSI A-D routes
advertised by this PE (if the PE uses different Next Hops, then
the PE MUST be (auto)configured with multiple import RTs, one per
each such Next Hop). The Local Administrator field of this Route
Target MUST be set to 0.
If the PE supports Route Target Constrain [RT-CONSTRAIN], the PE
SHOULD advertise this import Route Target within its own AS using
Route Target Constrains. To constrain distribution of the Route
Target Constrain routes to the AS of the advertising PE these
routes SHOULD carry the NO_EXPORT Community ([RFC1997]).
+ A PE MAY aggregate two or more S-PMSIs originated by the PE onto
the same P-Multicast tree. If the PE already advertises S-PMSI A-
D routes for these S-PMSIs, then aggregation requires the PE to
re-advertise these routes. The re-advertised routes MUST be the
same as the original ones, except for the PMSI tunnel attribute.
If the PE has not previously advertised S-PMSI A-D routes for
these S-PMSIs, then the aggregation requires the PE to advertise
(new) S-PMSI A-D routes for these S-PMSIs. The PMSI Tunnel
attribute in the newly advertised/re-advertised routes MUST carry
the identity of the P-Multicast tree that aggregates the S-PMSIs.
If at least some of the S-PMSIs aggregated onto the same P-
Multicast tree belong to different MVPNs, then all these routes
MUST carry an MPLS upstream assigned label [RFC5331].
If all these aggregated S-PMSIs belong to the same MVPN, and this
MVPN uses PIM as its C-multicast routing protocol, then the
corresponding S-PMSI A-D routes MAY carry an MPLS upstream
assigned label [RFC5331]. Moreover, in this case the labels MUST
be distinct on a per MVPN basis, and MAY be distinct on a per
route basis.
If all these aggregated S-PMSIs belong to the MVPN(s) that use
mLDP as its C-multicast routing protocol, then the corresponding
S-PMSI A-D routes MUST carry an MPLS upstream assigned label
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[RFC5331], and these labels MUST be distinct on a per route (per
mLDP FEC) basis, irrespective of whether the aggregated S-PMSIs
belong to the same or different MVPNs.
The Next Hop field of the MP_REACH_NLRI attribute of the route MUST
be set to the same IP address as the one carried in the Originating
Router's IP Address field.
The route always carries a set of Route Targets. The default set of
Route Targets is determined as follows:
+ If there is a (unicast) VPN-IP route to C-S originate from the
VRF, but no (unicast) VPN-IP route to C-RP originated from the
VRF, then the set of Route Targets is set to a set intersection
between the set of Route Targets carried in the intra-AS I-PMSI
A-D route originated from the VRF, and the set of Route Targets
carried by the (unicast) VPN-IP route to C-S.
+ If there is no (unicast) VPN-IP route to C-S originated from the
VRF, but there is a (unicast) VPN-IP route to C-RP originated
from the VRF, then the set of Route Targets is set to a set
intersection between the set of Route Targets carried in the
intra-AS I-PMSI A-D route originated from the VRF, and the set of
Route Targets carried by the (unicast) VPN-IP route to C-RP.
+ If there is a (unicast) VPN-IP route to C-S originate from the
VRF, and a (unicast) VPN-IP route to C-RP originated from the
VRF, then the set of Route Targets is set to a set intersection
between the set of Route Targets carried in the intra-AS I-PMSI
A-D route originated from the VRF, and the set union of Route
Targets carried by the (unicast) VPN-IP route to C-S and the
(unicast) VPN-IP route to C-RP.
In each of the above cases, an implementation MUST allow the set of
Route Targets carried by the route to be specified by configuration.
In the absence of a configured set of Route Targets, the route MUST
carry the default set of Route Targets, as specified above.
12.2. Handling S-PMSI A-D routes by ASBRs
Procedures for handling an S-PMSI A-D route by ASBRs (both within and
outside of the AS of the PE that originates the route) are the same
as specified in Section "Propagating Inter-AS Auto-Discovery
Information", except that instead of Inter-AS I-PMSI A-D routes the
procedures apply to S-PMSI A-D routes.
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12.2.1. Merging S-PMSI into an I-PMSI
Consider the situation where:
+ An ASBR is receiving (or expecting to receive) inter-AS (C-S, C-
G) data from upstream via an S-PMSI.
+ The ASBR is sending (or expecting to send) the inter-AS (C-S, C-
G) data downstream via an I-PMSI.
This situation may obtain if the upstream providers have a policy of
using S-PMSIs but the downstream providers have a policy of using I-
PMSIs. To support this situation, an ASBR MAY, under certain
conditions, merge one or more upstream S-PMSIs into a downstream I-
PMSI.
An S-PMSI (corresponding to a particular S-PMSI A-D route) MAY be
merged by a particular ASBR into an I-PMSI (corresponding to a
particular Inter-AS I-PMSI A-D route) if and only if the following
conditions all hold:
+ BGP is used to exchange C-multicast routes.
+ The S-PMSI A-D route and the Inter-AS I-PMSI A-D route originate
in the same AS. The Inter-AS I-PMSI A-D route carries the
originating AS in the Source AS field of the NLRI of the route,
and also in the AS_PATH attribute of the route. The S-PMSI A-D
route carries the originating AS in the AS_PATH attribute of the
route.
+ The S-PMSI A-D route and the Inter-AS I-PMSI A-D route have
exactly the same set of RTs.
+ For each (C-S,C-G) mentioned in the S-PMSI route, if the ASBR has
installed a Source Tree Join (C-S, C-G) C-multicast route, then
the S-PMSI route was originated by the upstream PE of the C-
multicast route. The address of the upstream PE is carried in the
RT of the C-multicast route. The address of the PE that
originated the S-PMSI route is carried in the Originating
Router's IP Addr field of the MCAST-VPN NLRI of the route.
+ The ASBR supports the optional capability to discard (C-S, C-G)
traffic received on an I-PMSI.
An ASBR performs merging by stitching the tail end of the P-tunnel,
as specified in the the PMSI Tunnel Attribute of the S-PMSI A-D route
received by the ASBR, to the to the head of the P-tunnel, as
specified in the PMSI Tunnel Attribute of the Inter-AS I-PMSI A-D
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route re-advertised by the ASBR.
IP processing during merge: If an ASBR merges an (C-S, C-G) S-PMSI A-
D route into an Inter-AS I-PMSI A-D route, the ASBR MUST discard all
(C-S, C-G) traffic it receives on the tunnel advertised in the I-PMSI
A-D route.
An ASBR that merges an S-PMSI A-D route into an Inter-AS I-PMSI A-D
route MUST NOT re-advertise the S-PMSI A-D route.
12.3. Receiving S-PMSI A-D routes by PEs
Consider a PE that receives an S-PMSI A-D route. If one or more of
the VRFs on the PE have their import Route Targets that contain one
or more of the Route Targets carried by the received S-PMSI A-D
route, then for each such VRF (and associated with it MVPN-TIB) the
PE performs the following.
Procedures for receiving an S-PMSI A-D route by a PE (both within and
outside of the AS of the PE that originates the route) are the same
as specified in Section "Inter-AS I-PMSI A-D route received via IBGP"
except that (a) instead of Inter-AS I-PMSI A-D routes the procedures
apply to S-PMSI A-D routes, and (b) a PE performs procedures
specified in that section only if in addition to the criteria
specified in that section one of the following is true:
+ the PE originates a Source Tree Join (C-S, C-G) C-multicast
route, and the upstream PE of that route is the PE that
originates the S-PMSI A-D route, or
+ the PE does not originate a Source Tree Join (C-S, C-G) C-
multicast route, but originates a Shared Tree Join (C-*, C-G) C-
multicast route, and the best (as determined by the BGP route
selection procedures) Source Active A-D route for (C-S, C-G)
selected by the PE is originated by the same PE as the one that
originates the S-PMSI A-D route, or
+ the PE does not originate a Source Tree Join (C-S, C-G), has not
received any Source Active A-D routes for (C-S, C-G), but does
originate a Shared Tree Join (C-*, C-G) route, and the upstream
PE for that route is the PE that originates the received S-PMSI
A-D route.
If the received S-PMSI A-D route has a PMSI Tunnel attribute with the
Leaf Information Required flag set to 1, then the PE originates a
Leaf A-D route. The Route Key of the Leaf A-D route is set to the
MCAST-VPN NLRI of the S-PMSI A-D route. The rest of the Leaf A-D
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route is constructed using the same procedures as specified in
section "Originating Leaf A-D route into IBGP", except that instead
of originating Leaf A-D routes in response to receiving Inter-AS I-
PMSI A-D routes the procedures apply to originating Leaf A-D routes
in response to receiving S-PMSI A-D routes.
In addition to the procedures specified in Section "Inter-AS I-PMSI
A-D route received via IBGP" the PE MUST set up its forwarding path
to receive (C-S, C-G) traffic from the tunnel advertised by the S-
PMSI A-D route (the PE MUST switch to the S-PMSI).
If a PE that is a leaf node of a particular Selective tunnel
determines that it no longer needs to receive any of (C-S, C-G)s
carried over that tunnel, the PE SHOULD prune itself off that tunnel.
Procedures for pruning are specific to a particular tunneling
technology.
13. Switching from Shared C-tree to Source C-tree
The procedures defined in this section only apply when the C-
multicast routing protocol is PIM [RFC4601], moreover only apply for
the multicast ASM mode, and MUST NOT be applied to Multicast Group
addresses belonging to the SSM range. The procedures also MUST NOT be
applied when the C-multicast routing protocol is BIDIR-PIM [RFC5015].
The procedures of this section are applicable only to MVPNs that use
both shared (i.e., rooted at a C-RP) and source (i.e., rooted at a C-
S) inter-site C-trees.
These procedures are not applicable to MVPNs that do not use shared
inter-site C-trees and rely solely on source inter-site C-trees. See
section ""Supporting PIM-SM without Inter-Site C-Shared Trees" for
the procedures applicable to that scenario.
Whether a given MPVN uses both inter-site shared and source C-trees
or not must be known a priori (e.g., via provisioning).
In the scenario where an MVPN customer switches from an C-RP based
tree (RPT) to the shortest path tree (SPT), in order to avoid packet
duplication choosing of a single consistent upstream PE, as described
in [MVPN], may not suffice. To illustrate this consider a set of PEs
{PE2, PE4, PE6} that are on the C-RP tree for (C-*, C-G) and have
chosen a consistent upstream PE, as described in [MVPN], for (C-*, C-
G) state. Further this upstream PE, say PE1, is using an MI-PMSI for
(C-*, C-G). If a site attached to one of these PEs, say PE2, switches
to the C-S tree for (C-S, C-G), PE2 generates a Source Tree Join C-
multicast route towards the upstream PE that is on the path to C-S,
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say PE3. PE3 also uses the MI-PMSI for (C-S, C-G), as PE1 uses for
(C-*, C-G). This results in {PE2, PE4, PE6} receiving duplicate
traffic for (C-S, C-G) - both on the C-RP tree (from PE1) and C-S
tree (from PE3). If it is desirable to suppress receiving duplicate
traffic then it is necessary to choose a single forwarder PE for (C-
S, C-G). The following describes how this is achieved.
13.1. Source Within a Site - Source Active Advertisement
Whenever as a result of receiving a Source Tree Join C-multicast
route for (C-S, C-G) from some other PE the local PE adds either the
S-PMSI or I-PMSI to the outgoing interface list of the (C-S, C-G)
state (see Section 11.3.1.1 "Receiving Source Tree Join C-multicast
route"), the local PE MUST originate a Source Active A-D route if the
PE has not originated such route already. The route carries a single
MCAST-VPN NLRI constructed as follows:
+ The RD in this NLRI is set to the RD of the VRF of the MVPN on
the PE.
+ The Multicast Source field MUST be set to C-S. The Multicast
Source Length field is set appropriately to reflect this.
+ The Multicast Group field MUST be set to C-G. The Multicast Group
Length field is set appropriately to reflect this.
The Next Hop field of the MP_REACH_NLRI attribute MUST be set to the
IP address that the PE places in the Global Administrator field of
the VRF Route Import extended community of the VPN-IP routes
advertised by the PE from the MVPN's VRF.
The route SHOULD carry the same set of Route Targets as the Intra-AS
I-PMSI A-D route of the MVPN originated by the PE.
Using the normal BGP procedures the Source Active A-D route is
propagated to all the PEs of the MVPN.
Note that the advertisement of a Source Active A-D route for a given
(C-S, C-G) could be combined, if desired, with the advertisement of
an S-PMSI A-D route for the same (C-S, C-G) This is accomplished by
using the same BGP Update message to carry both the NLRI of the S-
PMSI A-D route and the NLRI of the Source Active A-D route.
Note that even if the originating PE advertises both the Source
Active A-D route and the S-PMSI A-D route in the same BGP Update
message, an implementation can not assume that all other PEs will
receive both of these routes in the same Update message.
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Whenever as a result of receiving a withdrawal of the previousely
advertise Source Tree Join C-multicast route for (C-S, C-G), the PE
is going to remove the S-PMSI/I-PMSI from the outgoing interface list
of the (C-S, C-G) state, the local PE MUST also withdraw the Source
Active A-D route for (C-S, C-G), if such a route has been advertised.
Note that if the PE is also acting as a C-RP, but inter-site shared
trees are being used, the reception of a PIM Register message by the
PE does not result in the origination of a Source Active A-D route.
13.2. Receiving Source Active A-D route
When a PE receives a new Source Active A-D route from some other PE,
the PE finds a VRF whose import Route Targets match one or more of
the Route Targets carried by the route. If the match is found, then
the PE updates the VRF with the received route.
We say that a given (C-S, C-G) Source Active A-D route stored in a
given VRF on a PE matches a given (C-*, C-G) entry present in the
MVPN-TIB associated with the VRF if C-G carried by the route is the
same as C-G of the entry, and the PE originates a Shared Tree Join C-
multicast route for the same C-G as C-G of the entry.
When (as a result of receiving PIM messages from one of its CEs) a PE
creates in one of its MVPN-TIBs a (new) (C-*, C-G) entry with a non-
empty outgoing interface list that contains one or more PE-CE
interfaces, the PE MUST check if it has any matching Source Active A-
D routes. If there is one or more such matching route, such that the
PE does not have (C-S, C-G) state in its MVPN-TIB for (C-S, C-G)
carried in the route, then the PE selects one of them (using the BGP
route selection procedures), and sets up its forwarding path to
receive (C-S, C-G) traffic from the tunnel the originator of the
selected Source Active A-D route uses for sending (C-S, C-G).
When as a result of receiving a new Source Active A-D route a PE
updates its VRF with the route, the PE MUST check if the newly
received route matches any (C-*, C-G) entries. If (a) there is a
matching entry, (b) the PE does not have (C-S, C-G) state in its
MVPN-TIB for (C-S, C-G) carried in the route, and (c) the received
route is selected as the best(using the BGP route selection
procedures), then the PE sets up its forwarding path to receive (C-S,
C-G) traffic from the tunnel the originator of the selected Source
Active A-D route uses for sending (C-S, C-G).
Note that if the PE is also acting as a C-RP, and inter-site shared
trees are being used, the BGP Source Active A-D routes do not replace
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the MSDP or PIM-based Anycast RP peerings among C-RPs that would be
needed to disseminate source discovery information among C-RPs.
13.2.1. Pruning Sources off the Shared Tree
In addition to the procedures in the previous section, a PE applies
the following procedure when importing a Source Active A-D route for
(C-S,C-G) into a VRF.
The PE finds an (C-*, C-G) entry in the MVPN-TIB whose C-G is the
same as C-G carried in the Multicast Group field of the Source Active
A-D route.
If the outgoing interface list (oif) for the found (C-*, C-G) entry
in the MVPN-TIB on the PE contains either I-PMSI or S-PMSI, and the
PE does not originate the Source Tree Join C-multicast route for (C-
S, C-G) (where C-S is address carried in the Multicast Source field,
and C-G is the address carried in the Multicast Group field of the
received Source Active A-D route), then the PE MUST transition the
(C-S, C-G, rpt) downstream state machine on I-PMSI/S-PMSI to the
Prune state. [Conceptually the C-PIM state machine on the PE will act
"as if" it had received Prune (C-S, C-G,Rpt) on I-PMSI/S-PMSI,
without actually having received one.] Depending on the (C-S,C-G,rpt)
state of the PE-CE interfaces, this may result in the PE using PIM
procedures to prune C-S off the (C-*,C-G) tree.
Transitioning the state machine to the Prune state SHOULD be done
after a delay that is controlled by a timer. The value of the timer
MUST be configurable. The purpose of this timer is to ensure that C-S
is not pruned off the shared tree until all PEs have had time to
receive the Source Active A-D route for (C-S, C-G).
Note that before C-S is prune off the shared tree, there is a
possibility to have (C-S,C-G) packets be sent at the same time on the
PMSI by distinct PEs. This would result in a transient unnecessary
traffic on the provider backbone. However, no duplicates will reach
customer hosts subscribed to C-G as long as the downstream PEs apply
procedures described in section 9.1 of [MVPN].
The PE MUST keep the (C-S, C-G, rpt) downstream state machine on I-
PMSI/S-PMSI in the Prune state for as long as (a) the outgoing
interface list (oif) for the found (C-*, C-G) entry in the MVPN-TIB
on the PE contains either I-PMSI or S-PMSI, and (b) the PE has at
least one Source Active A-D route for (C-S, C-G), and (c) the PE does
not originate the Source Tree Join C-multicast route for (C-S, C-G).
Once either of these conditions become no longer valid, the PE MUST
transition the (C-S, C-G, rpt) downstream state machine on I-PMSI/S-
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PMSI to the NoInfo state.
Note that changing the state on the downstream state machine on I-
PMSI/S-PMSI, as described above, does not imply exchanging PIM
messages over I-PMSI/S-PMSI.
Note also, that except for the scenario described in the third
paragraph of this section, in all other scenarios relying solely on
PIM procedures on the PE is sufficient to ensure the correct behavior
when pruning sources off the shared tree.
14. Supporting PIM-SM without Inter-Site Shared C-trees
The procedures defined in this section only apply when the C-
multicast routing protocol is PIM [RFC4601], moreover only apply for
the multicast ASM mode, and MUST NOT be applied to Multicast Group
addresses belonging to the SSM range. The procedures also MUST NOT be
applied when the C-multicast routing protocol is BIDIR-PIM [RFC5015].
The procedures of this section are applicable only to MVPNs that do
not use inter-site shared (i.e., rooted at a C-RP) C-trees.
These procedures are not applicable to MVPNs that use both shared and
shortest path inter-site C-trees. See section "Switching from Shared
C-trees to Source C-trees" for the procedures applicable to that
scenario.
Whether a given MPVN uses inter-site shared C-trees or not must be
known a priori (e.g., via provisioning).
14.1. Discovering Active Multicast Sources
A PE can obtain information about active multicast sources within a
given MVPN in a variety of ways. One way is for the PE to act as a
fully functional customer RP (C-RP) for that MVPN. Another way is to
use PIM Anycast RP procedures [PIM-ANYCAST-RP] to convey information
about active multicast sources from one or more of the MVPN C-RPs to
the PE. Yet another way is to use MSDP [MSDP] to convey information
about active multicast sources from the MVPN C-RPs to the PE.
When a PE using any of the above methods first learns of a new
(multicast) source within that MVPN, the PE constructs a Source
Active A-D route, and sends this route to all other PEs that have one
or more sites of that MVPN connected to them. The route carries a
single MCAST-VPN NLRI constructed as follows:
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+ The RD in this NLRI is set to the RD of the VRF of the MVPN on
the PE.
+ The Multicast Source field MUST be set to the source IP address
of the multicast data packet carried in the PIM-Register message
(RP/PIM register case) or of the MSDP Source-Active message (MSDP
case). The Multicast Source Length field is set appropriately to
reflect this.
+ The Multicast Group field MUST be set to the group IP address of
the multicast data packet carried in the PIM-Register message
(RP/PIM register case) or of the MSDP Source-Active message (MSDP
case). The Multicast Group Length field is set appropriately to
reflect this.
The Next Hop field of the MP_REACH_NLRI attribute MUST be set to the
IP address that the PE places in the Global Administrator field of
the VRF Route Import extended community of the VPN-IP routes
advertised by the PE.
The route SHOULD carry the same set of Route Targets as the Intra-AS
I-PMSI A-D route of the MVPN originated by the PE.
Using the normal BGP procedures the Source Active A-D route is
propagated to all the PEs of the MVPN.
When a PE that previously advertised a Source Active A-D route for a
given (multicast) source learns that the source is no longer active
(the PE learns this by using the same mechanism by which the PE
learned that the source was active), the PE SHOULD withdraw the
previously advertised Source Active route.
14.2. Receiver(s) Within a Site
A PE follows the procedures specified in Section "Originating C-
multicast routes by a PE", except that the procedures specified in
Section "Originating Shared Tree Join C-multicast route" are replaced
with the procedures specified in this Section below.
When a PE receives a new Source Active A-D route, the PE finds a VRF
whose import Route Targets match one or more of the Route Targets
carried by the route. If the match is found, then the PE updates the
VRF with the received route.
We say that a given (C-S, C-G) Source Active A-D route stored in a
given VRF matches a given (C-*, C-G) entry present in the MVPN-TIB
associated with the VRF if C-G carried by the route is the same as C-
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G of the entry.
When (as a result of receiving PIM messages from one of its CEs) a PE
creates in one of its MVPN-TIBs a (new) (C-*, C-G) entry with a non-
empty outgoing interface list that contains one or more PE-CE
interfaces, the PE MUST check if it has any matching Source Active A-
D routes. If there is one or more such matching routes, and the best
path to C-S carried in the matching route(s) is reachable through
some other PE, then for each such route the PE MUST originate a
Source Tree Join C-multicast route. If there is one or more such
matching routes, and the best path to C-S carried in the matching
route(s) is reachable through a CE connected to the PE, then for each
such route the PE MUST originate a PIM Join (C-S, C-G) towards the
CE.
When as a result of receiving a new Source Active A-D route a PE
updates its VRF with the route, the PE MUST check if the newly
received route matches any (C-*, C-G) entries. If there is a matching
entry, and the best path to C-S carried in the (A-D) route is
reachable through some other PE, the PE MUST originate a Source Tree
Join C-multicast route for the (C-S, C-G) carried by the route. If
there is a matching entry, and the best path to C-S carried in the
(A-D) route is reachable through a CE connected to the PE, the PE
MUST originate a PIM Join (C-S, C-G) towards the CE.
Construction and distribution of the Source Tree Join C-multicast
route follows the procedures specified in Section "Originating Source
Tree Join C-multicast route", except that the Multicast Source
Length, Multicast Source, Multicast Group Length, and Multicast Group
fields in the MCAST-VPN NLRI of the Source Tree Join C-multicast
route are copied from the corresponding field in the Source Active A-
D route.
A PE MUST withdraw a Source Tree Join C-multicast route for (C-S, C-
G) if, as a result of having received PIM messages from one of its
CEs, the PE creates a Prune (C-S, C-G, RPT-bit) upstream state in one
of its MVPN-TIBs, but has no (C-S, C-G) Joined state in that MVPN-
TIB, and had previously advertised the said route. (This is even if
the VRF associated with the MVPN-TIB still has a (C-S, C-G) Source
Active A-D route).
A PE MUST withdraw a Source Tree Join C-multicast route for (C-S, C-
G) if the Source Active A-D route that triggered the advertisement of
the C-multicast route is withdrawn.
When a PE deletes the (C-*, C-G) state (e.g., due to to receiving PIM
Prune (C-*, C-G) from its CEs), the PE MUST withdraw all the Source
Tree Join C-multicast routes for C-G that have been advertised by the
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PE, except for the routes for which the PE still maintains the
corresponding (C-S, C-G) state.
Even though PIM is used as a C-multicast protocol, procedures
described in Section "Originating Shared Tree Join C-multicast route"
do not apply here, as only the Source Tree Join C-multicast routes
are exchanged among PEs.
14.3. Receiving C-multicast routes by a PE
In this model the only valid type of a C-multicast route that a PE
could receive is a Source Tree Join C-multicast route. Processing of
such a route follows the procedures specified in Section "Receiving
Source Tree Join C-multicast route".
15. Carrier's Carrier
A way to support the Carrier's Carrier model is provided by using
mLDP as the CE-PE multicast routing and label distribution protocol,
as specified in this document.
To improve scalability it is RECOMMENDED that for the Carrier's
Carrier scenario within an AS all the S-PMSIs of a given MVPN be
aggregated into a single P-Multicast tree (by using upstream assigned
labels).
16. Scalability Considerations
A PE should use Route Target Constrain [RT-CONSTRAIN] to advertise
the Route Targets that the PE uses for the VRF Route Imports extended
community (note that doing this requires just a single Route Target
Constraint advertisement by the PE). This allows each C-multicast
route to reach only the relevant PE, rather than all the PEs
participating the an MVPN.
To keep the intra-AS membership/binding information within the AS of
the advertising router the BGP Update message originated by the
advertising router SHOULD carry the NO_EXPORT Community ([RFC1997]).
An Inter-AS I-PMSI A-D route originated by an ASBR aggregates Intra-
AS I-PMSI A-D routes originated within the ASBR's own AS. Thus while
the Intra-AS I-PMSI A-D routes originated within an AS are at the
granularity of <PE, MVPN> within that AS, outside of that AS the
(aggregated) Inter-AS I-PMSI A-D routes are at the granularity of
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<AS, MVPN>. An Inter-AS I-PMSI A-D route for a given <AS, MVPN>
indicates the presence of or or more sites of the MVPN connected to
the PEs of the AS.
For a given inter-AS tunnel each of its intra-AS segments could be
constructed by its own mechanism. Moreover, by using upstream
assigned labels within a given AS multiple intra-AS segments of
different inter-AS tunnels of either the same or different MVPNs may
share the same P-Multicast tree.
Since (aggregated) Inter-AS I-PMSI A-D routes may have granularity of
<AS, MVPN>, an MVPN that is present in N ASes would have total of N
inter-AS tunnels. Thus for a given MVPN the number of inter-AS
tunnels is independent of the number of PEs that have this MVPN.
Within each Autonomous System BGP Route reflectors can be partitioned
among MVPNs present in that Autonomous System so that each partition
carries routes for only a subset of the MVPNs supported by the
Service Provider. Thus no single Route Reflector is required to
maintain routes for all MVPNs. Moreover, Route Reflectors used for
MVPN do not have to be used for VPN-IP routes (although they may be
used for VPN-IP routes as well).
As described in Section "C-multicast routes aggregation", C-multicast
routes for a given (S,G) of a given MVPN originated by PEs that are
clients of a given Route Reflector are aggregated by the Route
Reflector. Therefore, even if within a Route Reflector cluster there
are multiple C-multicast routes for a given (S,G) of a given MVPN,
outside of the cluster all these routes are aggregated into a single
C-multicast route. Additional aggregation of C-multicast routes
occurs at ASBRs, where an ASBR aggregates all the received C-
multicast routes for a given (S,G) of a given MVPN into a single C-
multicast route. Moreover, both Route Reflectors and ASBRs maintain
C-multicast routes only in the control plane, but not in the data
plane.
16.1. Dampening C-multicast routes
The rate of C-multicast routing changes advertised by a PE is not
necessarily directly proportional to the rate of multicast routing
changes within the MVPN sites connected to the PE, as after the first
(C-S,C-G) Join originated within a site, all the subsequent Joins for
same (C-S,C-G) originated within the sites of the same MVPN connected
to the PE do not cause origination of new C-multicast routes by the
PE.
Depending on how multicast VPN is engineered, dynamic addition and
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removal of P2MP RSVP-TE leaves through advertisement/withdrawal of
Leaf A-D routes, will happen. Dampening techniques can be used to
limit corresponding processing.
To lessen the control plane overhead associated with processing of C-
multicast routes, this document proposes OPTIONAL route dampening
procedures similar to what is described in RFC2439. The following
OPTIONAL procedures can be enabled on a PE, ASBR, or BGP Route
Reflector advertising or receiving C-multicast routes.
16.1.1. Dampening withdrawals of C-multicast routes
A PE/ASBR/Route Reflector can OPTIONALLY delay the advertisement of
withdrawals of C-multicast routes. An implementation SHOULD provide
the ability to control the delay via a configurable timer, possibly
with some backoff algorithm to adapt the delay to multicast routing
activity.
Dampening of withdrawals of C-multicast routes does not impede the
multicast join latency observed by MVPN customers, and also does not
impede the multicast leave latency observed by a CE, as multicast
forwarding from the VRF will stop as soon as C-multicast state is
removed in the VRF.
The potential drawbacks of dampening of withdrawals of C-multicast
routes are:
+ Until the withdrawals are actually sent, multicast traffic for
the C-multicast routes in question will be continued to be
transmitted to the PE, which will just have to discard it. Note
that the PE may receive useless (multicast) traffic anyway,
irrespective of dampening of withdrawals of C-multicast routes
due to the use of I-PMSIs.
+ Any state in the upstream PEs that would be removed as a result
of processing the withdrawals will remain until the withdrawals
are sent.
Discussion on whether the potential drawbacks mentioned above are of
any practical significance is outside the scope of this document.
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16.1.2. Dampening Source/Shared Tree Join C-multicast routes
A PE/ASBR/Route Reflector can OPTIONALLY delay the advertisement of
Source/Shared Tree Join C-multicast routes. An implementation SHOULD
provide the ability to control the delay via a configurable timer,
possibly with some backoff algorithm to adapt the delay to multicast
routing activity.
Dampening Source/Shared Tree Join C-multicast routes will not impede
multicast join latency observed by a given MVPN, except if the PE
advertising the Source/Shared Tree Join C-multicast route for a
particular C-S/C-RP is the first to do so for all the sites of the
MVPN that share the same upstream PE with respect to the C-S/C-RP.
16.2. Dampening withdrawals of Leaf A-D routes
Similarly to the procedures proposed above for withdrawal of C-
multicast routes, dampening can be applied to the withdrawal of Leaf
A-D routes.
17. Security Considerations
The mechanisms described in this document could re-use the existing
BGP security mechanisms.
A PE router MUST NOT accept from CEs routes with MCAST-VPN SAFI.
If BGP is used as a CE-PE routing protocol, then when PE receives a
route from CE, if this route carries the VRF Route Import extended
community, the PE MUST remove this community from the route before
turning it into a VPN-IP route. Routes that a PE advertises to a CE
MUST NOT carry the VRF Route Import extended community.
It is important to protect the control plane resources within the PE
to prevent any one VPN from hogging excessive resources. This is the
subject of the remainder of the security considerations section.
When C-multicast routing information is exchanged among PEs using
BGP, an implementation SHOULD provide the ability to rate limit BGP
messages used for this exchange. This SHOULD be provided on a per PE,
per MVPN granularity.
An implementation SHOULD provide capabilities to impose an upper
bound on the number of S-PMSI A-D routes, as well as on how
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frequently they may be originated. This SHOULD be provided on a per
PE, per MVPN granularity.
In conjunction with the procedures specified in Section "Supporting
PIM-SM without Inter-Site Shared C-trees" an implementation SHOULD
provide capabilities to impose an upper bound on the number of Source
Active A-D routes, as well as on how frequently they may be
originated. This SHOULD be provided on a per PE, per MVPN
granularity.
In conjunction with the procedures specified in Section "Switching
from Shared C-tree to Source C-tree" limiting the amount of (C-S,C-G)
state would limit the amount of Source Active A-D route, as in the
context of this section Source Active A-D routes are created in
response to Source Tree Join C-multicast routes, and Source Tree Join
C-multicast routes are created as a result of creation of (C-S, C-G)
state on PEs. However, to provide an extra level of robustness in the
context of these procedures an implementation MAY provide
capabilities to impose an upper bound on the number of Source Active
A-D routes, as well as on how frequently they may be originated.
This MAY be provided on a per PE, per MVPN granularity.
Section "Dampening withdrawals of C-multicast routes" describes
optional procedures for dampening withdrawals of C-multicast routes.
It is RECOMMENDED that an implementation supports such procedures.
Section "Dampening withdrawals of Leaf A-D routes" describes optional
procedures for dampening withdrawals of Leaf A-D routes. It is
RECOMMENDED that an implementation supports such procedures.
18. IANA Considerations
This document defines a new BGP Extended Community called Source AS.
This community is 2-octet AS specific, of an extended type, and is
transitive.
This document defines a new BGP Extended Community called VRF Route
Import. This community is IP address specific, of an extended type,
and is transitive.
This document defines a new NLRI, called MCAST-VPN, to be carried in
BGP using multiprotocol extensions. It requires assignment of a new
SAFI.
This document defines a new BGP optional transitive attribute, called
PMSI Tunnel.
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19. Acknowledgement
Some of the text in Section "Supporting PIM-SM without Inter-Site
Shared C-trees" has been taken almost verbatim from RFC3618. We would
like to thank Chaitanya Kodeboniya for helpful discussions. We would
also like to thank members of the L3VPN IETF Working Group for
insightful comments and review.
20. Authors' Addresses
Rahul Aggarwal
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
Email: rahul@juniper.net
Eric C. Rosen
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA, 01719
E-mail: erosen@cisco.com
Thomas Morin
France Telecom R & D
2, avenue Pierre-Marzin
22307 Lannion Cedex
France
Email: thomas.morin@francetelecom.com
Yakov Rekhter
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
Email: yakov@juniper.net
21. References
21.1. Normative References
[IANA-SAFI] http://www.iana.org/assignments/safi-namespace
[MVPN] E. Rosen, R. Aggarwal [Editors], "Multicast in MPLS/BGP IP
VPNs", draft-ietf-l3vpn-2547bis-mcast
[RFC1997] R. Chandra, P. Traina, T. Li, "BGP Communities Attribute",
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RFC1997, August 1996.
[RFC2119] "Key words for use in RFCs to Indicate Requirement
Levels.", Bradner, RFC2119, March 1997.
[RFC4271] Rekhter, Y., Li, T., Hares, S., "A Border Gateway Protocol
4 (BGP-4)", RFC 4271, January 2006
[RFC4760] Bates, T., Rekhter, Y., Chandra, R., and D. Katz,
"Multiprotocol Extensions for BGP-4", RFC 4760, January 2007.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, February 2006.
[RFC4364] E. Rosen, Y. Rekhter, "BGP/MPLS IP Virtual Private Networks
(VPNs)", RFC4364, February 2006
[RFC4601] B. Fenner et. al., "Protocol Independent Multicast - Sparse
Mode (PIM-SM): Protocol Specification (Revised)", RFC 4601, August
2006
[RFC4659] J. De Clercq et. al., "BGP-MPLS IP Virtual Private Network
(VPN) Extension for IPv6 VPN", RFC 4659, September 2006
21.2. Informative References
[RFC5331] R. Aggrwal, Y. Rekhter, E. Rosen, " MPLS Upstream Label
Assignment and Context Specific Label Space", RFC 5331, August 2008
[RT-CONSTRAIN] P. Marques et. al., "Constrained Route Distribution
for Border Gateway Protocol/MultiProtocol Label Switching (BGP/MPLS)
Internet Protocol (IP) Virtual Private Networks (VPNs)", RFC 4684,
November 2006
[mLDP] I. Minei et. al., "Label Distribution Protocol Extensions for
Point-to-Multipoint and Multipoint-to-Multipoint Label Switched
Paths", draft-ietf-mpls-ldp-p2mp
[RFC4607] H. Holbrook, B. Cain "Source-Specific Multicast for IP",
RFC 4607, August 2006
[RFC5015] M. Handley et. al., "Bidirectional Protocol Independent
Multicast (BIDIR-PIM)", RFC5015, October 2007
[RFC4875] R. Aggarwal et. al., "Extensions to RSVP-TE for Point-to-
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Multipoint TE LSPs", RFC 4875, May 2007
[PIM-ANYCAST-RP] D. Farinacci, Y. Cai, "Anycast-RP using PIM" RFC
4610, August 2006
[MSDP] B. Fenner, D. Meyer, "Multicast Source Discovery Protocol
(MSDP)", RFC3618, October 2003
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