Network Working Group R. Aggarwal
Internet Draft Juniper Networks
Expiration Date: January 2008
Intended Status: Proposed Standard
E. Rosen
Cisco Systems, Inc.
T. Morin
France Telecom
Y. Rekhter
Juniper Networks
C. Kodeboniya
July 2007
BGP Encodings and Procedures for Multicast in MPLS/BGP IP VPNs
draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt
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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 auto-discovery route .................. 7
4.2 Inter-AS I-PMSI auto-discovery route .................. 8
4.3 S-PMSI auto-discovery route ........................... 8
4.4 Leaf auto-discovery route ............................. 9
4.5 Source Active auto-discovery route .................... 9
4.6 C-multicast route ..................................... 10
5 P-Multicast Service Interface Tunnel (PMSI Tunnel) attribute 11
6 Source AS Extended Community .......................... 13
7 VRF Route Import Extended Community ................... 14
8 MVPN Auto-Discovery/Binding ........................... 15
8.1 MVPN Auto-Discovery/Binding - Intra-AS Operations ..... 15
8.1.1 Originating (intra-AS) auto-discovery routes .......... 15
8.1.2 When not to originate (intra-AS) auto-discovery routes . 17
8.1.3 Receiving (intra-AS) auto-discovery routes ............ 17
8.2 MVPN Auto-Discovery/Binding - Inter-AS Operations ..... 19
8.2.1 Originating inter-AS auto-discovery routes ............ 20
8.2.2 When not to originate inter-AS auto-discovery routes .. 21
8.2.3 Propagating inter-AS auto-discovery routes ............ 21
8.2.3.1 Propagating inter-AS auto-discovery routes - Overview . 21
8.2.3.2 Inter-AS auto-discovery route received via EBGP ....... 22
8.2.3.3 Leaf auto-discovery route received via EBGP ........... 24
8.2.3.4 Inter-AS auto-discovery route received via IBGP ....... 24
8.2.3.5 Leaf auto-discovery route received via IBGP ........... 27
9 Non-congruent Unicast and Multicast Connectivity ...... 27
10 VPN C-Multicast Routing Information Exchange among PEs . 29
10.1 Originating C-multicast routes by a PE ................ 29
10.1.1 Originating routes with PIM as the C-Multicast protocol. 29
10.1.1.1 Originating Source Tree Join C-multicast route ........ 29
10.1.1.2 Originating Shared Tree Join C-multicast route ........ 29
10.1.2 Originating routes with mLDP as the C-Multicast protocol 30
10.1.3 Constructing the rest of the C-multicast route ........ 30
10.1.4 Unicast Route Changes ................................. 32
10.2 Propagating C-multicast routes by an ASBR ............. 32
10.3 Receiving C-multicast routes by a PE .................. 33
10.3.1 Receiving routes with PIM as the C-Multicast protocol . 33
10.3.1.1 Receiving Source Tree Join C-multicast route .......... 34
10.3.1.2 Receiving Shared Tree Join C-multicast route .......... 34
10.3.2 Receiving routes with mLDP as the C-Multicast protocol . 34
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10.4 C-multicast routes aggregation ........................ 35
11 Switching to S-PMSI ................................... 36
11.1 Originating S-PMSI auto-discovery routes .............. 36
11.2 Handling S-PMSI auto-discovery routes by ASBRs ........ 37
11.3 Receiving S-PMSI auto-discovery routes by PEs ......... 37
12 Carrier's Carrier ..................................... 38
13 Choosing a single forwarder PE when switching from RPT to SPT 38
13.1 Source Within a Site - Source Active Advertisement .... 39
13.2 Receiving Source Active auto-discovery route .......... 39
13.2.1 Pruning Sources off the Shared Tree ................... 40
14 Supporting PIM-SM without inter-site Shared Trees ..... 41
14.1 Multicast Source Within a Site - Source Active Advertisement 41
14.2 Receiver(s) Within a Site ............................. 42
14.3 Receiving C-multicast routes by a PE .................. 43
15 Scalability Considerations ............................ 43
16 Dampening C-multicast routes .......................... 44
16.1 Dampening withdrawals of C-multicast routes ........... 45
16.2 Dampening Source/Shared Tree Join C-multicast routes .. 45
17 Dampening withdrawals of leaf auto-discovery routes ... 46
18 IANA Consideration .................................... 46
19 Security Considerations ............................... 46
20 Acknowledgement ....................................... 46
21 References ............................................ 46
21.1 Normative References .................................. 46
21.2 Informative References ................................ 47
22 Author Information .................................... 48
23 Intellectual Property Statement ....................... 48
24 Copyright Notice ...................................... 49
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 a new BGP attribute, P-Multicast Service
Interface Tunnel (PMSI Tunnel) 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". For a given MVPN there are the following types of auto-
discovery routes:
+ intra-AS auto-discovery route (auto-discovery route);
+ inter-AS auto-discovery route;
+ S-PMSI auto-discovery route;
+ intra-AS segment leaf auto-discovery route (leaf auto-discovery
route);
+ Source Active auto-discovery 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.
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 auto-discovery
routes:
+ 1 - Intra-AS I-PMSI auto-discovery route (or just auto-discovery
route);
+ 2 - Inter-AS I-PMSI auto-discovery route (or just inter-AS auto-
discovery route);
+ 3 - S-PMSI auto-discovery route;
+ 4 - Intra-AS segment leaf auto-discovery route (or just leaf
auto-discovery route).
+ 5 - Source Active auto-discovery 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
auto-discovery routes, Source Active auto-discovery 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 auto-discovery route
An intra-AS I-PMSI auto-discovery 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 auto-discovery routes is described in
Section "MVPN Auto-Discovery/Binding - Intra-AS Operations".
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4.2. Inter-AS I-PMSI auto-discovery route
An inter-AS I-PMSI auto-discovery 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 low order two octets of the Source AS
field.
Usage of inter-AS I-PMSI auto-discovery routes is described in
Section "MVPN Auto-Discovery/Binding - Inter-AS Operations".
4.3. S-PMSI auto-discovery route
An S-PMSI auto-discovery 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-Generic LSP
Identifier Value. If the Multicast Group field contains an IPv4
address or a C-Generic LSP Identifier Value, 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 S-PMSI auto-discovery routes is described in Section
"Switching to S-PMSI".
4.4. Leaf auto-discovery route
A leaf auto-discovery route type specific MCAST-VPN NLRI consists of
the following:
+-----------------------------------+
| Route Key (variable) |
+-----------------------------------+
| Originating Router's IP Addr |
+-----------------------------------+
Usage of Leaf auto-discovery routes is described in Section "MVPN
Auto-Discovery/Binding - Inter-AS Operations".
4.5. Source Active auto-discovery route
A Source Active auto-discovery 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
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contains an IPv6 address, then the value of the Multicast Source
Length field is 128.
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 auto-discovery 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 auto-discovery routes is described in Sections
"Choosing a single forwarder PE when switching from RPT to SPT", and
"Supporting PIM-SM without inter-site Shared Trees".
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
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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-Generic LSP
Identifier Value. If the Multicast Group field contains an IPv4
address or C-Generic LSP Identifier Value, 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 "VPN C-multicast
Routing Information Exchange among PEs".
5. P-Multicast Service Interface Tunnel (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:
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+ 1 - RSVP-TE P2MP LSP
+ 2 - LDP P2MP LSP
+ 3 - PIM-SSM Tree
+ 4 - PIM-SM Tree
+ 5 - PIM-Bidir Tree
+ 6 - Ingress Replication
+ 7 - LDP 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 RSVP-TE P2MP LSP, the Tunnel Identifier is
<Extended Tunnel ID, P2MP ID> as carried in the RSVP-TE P2MP LSP
SESSION Object [RSVP-TE-P2MP].
When the type is set to LDP P2MP LSP, the Tunnel Identifier is <Root
Node Address, Generic LSP Identifier Value>, as carried in the P2MP
FEC [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 expected to be the same group for all intra-AS
auto-dicovery routes for the same MVPN. According to [RFC4607], the
group address can be locallty 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
auto-discovery 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.
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When the type is set to Ingress Replication the Tunnel Identifier
carries the unicast tunnel endpoint IP address.
When the type is set to LDP MP2MP LSP, the Tunnel Identifier is <P-
Root Node Address, Generic LSP Identifier Value>, as carried in the
MP2MP FEC [mLDP]. The Generic LSP Identifier Value SHOULD be the same
for all intra-AS auto-discovery routes for the same MVPN originated
by PEs within a given AS. How this Value is chosen is outside the
scope of this specification.
If LDP MP2MP LSPs are used as PMSI tunnels, the router that
transmitted a given packet into the tunnel cannot be identified. As
a result, LDP MP2MP LSPs do not support aggregation, and therefore
can only be used as unaggregated tunnels. Support of aggregation with
LDP MP2MP LSPs is a matter for further study. In addition, if an LDP
MP2MP LSP is used within a given AS as an intra-AS segment of an
inter-AS tunnel, a single ASBR within that AS must be chosen to be
the one which transmits packets to and from the upstream segment of
the inter-AS tunnel. In the absence of the procedures for doing this,
LDP MP2MP LSPs can not be used for intra-AS segments of inter-AS
tunnels. Procedures for choosing a single ASBR are a matter for
further study. Finally, use of LDP MP2MP LSPs makes choosing a single
forwarder PE (see Section "Choosing a single forwarder PE when
switching from RPT to SPT") mandatory.
The PMSI Tunnel attribute is used in conjunction with intra-AS and
inter-AS I-PMSI auto-discovery routes, with S-PMSI auto-discovery
routes, and with leaf auto-discovery 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].
To support MVPN a PE that originates a (unicast) route to VPN-IP
addresses MUST include in the BGP Update message that carries this
route the Source AS extended community, except if it is known a
priori that none of these addresses will act as multicast sources
and/or RP, in which case the (unicast) route need not carry the
Source AS extended community. 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.
Usage of the 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 RP, in which case the VRF
need not have this import Route Target. This Router Target extended
community MUST be unique to this VRF, and MUST be an IP address
specific extended community. It is constructed as follows:
+ The Global Administrator field of the Route Target 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 Route Target 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).
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 this Route
Target, except if it is known a priori that none of these addresses
will act as multicast sources and/or RP, in which case the (unicast)
route need not carry the VRF Route Import extended community.
If a PE uses Route Target Constrain [RT-CONSTRAIN], the PE SHOULD
advertise all such import Route Targets 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".
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8. 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.
MVPN auto-discovery/binding consists of two components: intra-AS and
inter-AS. The former provides MVPN auto-discovery/binding within a
single AS. The latter provides MVPN auto-discovery/binding across
multiple ASes.
Note that the inter-AS component applies only to the ASes that use
either option (b) or (c) for unicast inter-AS operations, as
specified in Section "Multi-AS Backbones" of [RFC4364]. ASes that use
option (a) need only the intra-AS component.
8.1. MVPN Auto-Discovery/Binding - Intra-AS Operations
This section describes exchanges of auto-discovery routes
originated/received by PEs within the same AS.
8.1.1. Originating (intra-AS) auto-discovery 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
in Section "When not to originate (intra-AS) auto-discovery route",
originate an auto-discovery 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
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 a default
I-PMSI is used for the MVPN. Depending on the technology used to
instantiate the provider tunnel for the MVPN on the PE, the PMSI
Tunnel attribute of the intra-AS auto-discovery route is constructed
as follows.
+ If the PE that originates the advertisement uses a P-Multicast
tree to instantiate the provider tunnel for the MVPN, the PMSI
Tunnel attribute MUST contain the identity of the tree that is
used to instantiate the tunnel (note that the PE could create the
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identity of the tree prior to the actual instantiation of the
tunnel). If in order to instantiate the provider tunnel the PE
needs to know the leaves of the tree, then the PE obtains this
information from the intra-AS auto-discovery routes received from
other PEs.
+ A PE that uses a P-Multicast tree to instantiate the provider
tunnel MAY aggregate two or more MVPNs present on the PE onto the
same tree. If the PE already advertises intra-AS auto-discovery
routes for these MVPNs, 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 intra-AS auto-discovery
routes for these MVPNs, then the aggregation requires the PE to
advertise (new) intra-AS auto-discovery routes for these MVPNs.
The PMSI Tunnel attribute in the newly advertised/re-advertised
routes MUST carry the identity of the P-Multicast tree that
aggregates the MVPNs, as well as an MPLS upstream assigned label
[MPLS-UPSTREAM]. Each re-advertised route MUST have a distinct
label.
+ If the PE that originates the advertisement uses ingress
replication to instantiate the provider 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.
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.
The Next Hop field of the MP_REACH_NLRI attribute of the route SHOULD
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 auto-discovery 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 auto-
discovery 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
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set of Route Targets used for the auto-discovery 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]).
8.1.2. When not to originate (intra-AS) auto-discovery routes
If for a given MVPN all of its sites connected to a given PE are
known a priori to have no multicast sources, then this PE is NOT
REQUIRED to originate an auto-discovery route for that MVPN at all,
unless either
+ (a) some other PEs that have VRFs in that MVPN and are in the
same AS as the original PE use RSVP TE P2MP LSPs for that MVPN,
in which case the PE originates an auto-discovery route, but with
no PMSI Tunnel attribute, or
+ (b) the PE uses ingress replication for incoming multicast
traffic of that MVPN, in which case the PE originates an auto-
discovery route with the PMSI Tunnel attribute indicating ingress
replication.
If for a given MVPN all of its sites connected to a given PE are
known a priori to have no multicast receivers, and the PE uses
ingress replication for that MVPN then this PE is NOT REQUIRED to
originate an auto-discovery route for that MVPN at all.
8.1.3. Receiving (intra-AS) auto-discovery routes
When a PE receives a BGP Update message that carries an auto-
discovery route such that (a) the route was originated by some other
PE within the same AS as the local PE, (b) 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, 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 carries the PMSI Tunnel attribute then:
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+ 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 LDP
P2MP LSP, or PIM-SSM tree, or PIM-SM tree, or PIM-Bidir tree, the
PE SHOULD join the P-Multicast tree whose identity is carried in
the Tunnel Identifier.
+ If the Tunnel Type in the PMSI Tunnel attribute is set to RSVP-TE
P2MP LSP, the receiving PE has to establish the appropriate state
to properly handle the traffic received over that LSP. 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.
+ 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 VRF that
has at least one of its import Route Targets that matches one of
the Route Targets of the received auto-discovery route.
+ If the PMSI Tunnel attribute has the Tunnel Type set to LDP 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 VRF that has at least one of its import Route Target
that matches one of the Route Targets of the received auto-
discovery 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.
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8.2. MVPN Auto-Discovery/Binding - Inter-AS Operations
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
auto-discovery 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 of what is required for unicast).
+ The ASBR MUST be configured with an import Route Target that 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 inter-AS auto-discovery routes and S-PMSI auto-discovery
routes advertised by this ASBR (if the ASBR uses different Next
Hops, then the ASBR MUST be 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 ASBR supports Route
Target Constrain [RT-CONSTRAIN], the ASBR SHOULD advertise this
import Route Target within its own AS using Route Target
Constrains. Note that this Route Target controls acceptance of
leaf auto-discovery routes and C-multicast routes by the ASBR,
and is used to constrain distribution of both leaf auto-discovery
routes and C-multicast routes (see Section "VPN C-Multicast
Routing Information Exchange among PEs"). 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.
+ If the ASBR originates an inter-AS auto-discovery route for a
particular MVPN present on some of the PEs within its own AS, the
ASBR MUST be configured with an RD for that MVPN. To allow
aggregation of inter-AS auto-discovery routes it is RECOMMENDED
that all the ASBRs within an AS that are configured to originate
an inter-AS auto-discovery 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).
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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 the following
procedures.
8.2.1. Originating inter-AS auto-discovery 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 auto-discovery 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 a
default I-PMSI is used for the MVPN. The Tunnel Type in the
attribute is set to Ingress Replication; 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.
+ By default the route MUST carry the export Route Target used by
the unicast routing of that VPN. The default could be modified
via configuration by having a set of Route Targets used for the
inter-AS auto-discovery routes being distinct from the ones used
by the unicast routing of that VPN (see also Section "Non-
congruent Unicast and Multicast Connectivity").
An inter-AS auto-discovery route for a given <AS, MVPN> indicates
presence of the MVPN sites connected to one or more PEs of the AS.
An inter-AS auto-discovery route originated by an ASBR aggregates
(intra-AS) auto-discovery routes originated within the ASBR's own AS.
Thus while the auto-discovery routes originated within an AS are at
the granularity of <PE, MVPN> within that AS, outside of that AS the
(aggregated) inter-AS auto-discovery routes could be at the
granularity of <AS, MVPN>.
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8.2.2. When not to originate inter-AS auto-discovery 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 are NOT REQUIRED to originate an Inter-AS auto-
discovery route for that MVPN at all.
8.2.3. Propagating inter-AS auto-discovery routes
An inter-AS auto-discovery route for a given MVPN originated by an
ASBR within a given AS is propagated via BGP to other ASes.
8.2.3.1. Propagating inter-AS auto-discovery routes - Overview
Suppose that an ASBR A installs an inter-AS auto-discovery 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
auto-discovery 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 auto-discovery 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
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 auto-discovery 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
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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 instantiating a particular 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 will be present in the
inter-AS auto-discovery routes. But if the P-Multicast tree
instantiating 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 auto-
discovery" routes. The precise conditions under which leaf auto-
discover routes need to be used are described in subsequent sections.
Since (aggregated) inter-AS auto-discovery 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 is independent of the number of PEs that have this
MVPN.
The precise rules for distributing and processing the inter-AS auto-
discovery routes across ASes are given in the following sections.
8.2.3.2. Inter-AS auto-discovery route received via EBGP
When an ASBR receives from one of its EBGP neighbors a BGP Update
message that carries an inter-AS auto-discovery 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 to the
destination carried in the NLRI of the route, the ASBR re-advertises
this auto-discovery route to other PEs and ASBRs within its own AS
(handling of this route by other PEs and ASBRs is described in
Section "Inter-AS auto-discovery route received via IBGP").
When re-advertising an inter-AS auto-discovery 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 auto-discovery 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
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Tunnel attribute of the re-advertised inter-AS auto-discovery route
as follows.
+ If the ASBR uses ingress replication to instantiate 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 to instantiate the intra-AS
segment of the inter-AS tunnel, the PMSI Tunnel attribute MUST
contain the identity of the tree that is used to instantiate the
segment (note that the ASBR could create the identity of the tree
prior to the actual instantiation of the segment). If in order
to instantiate the segment the ASBR needs to know the leaves of
the tree, then the ASBR obtains this information from the leaf
auto-discovery routes received from other PEs/ASBRs in ASBR's own
AS (as described in Section "Leaf auto-discovery 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 to instantiate the intra-AS
segment of the inter-AS tunnel MAY aggregate two or more MVPNs
present on the ASBR onto the same tree. If the ASBR already
advertises inter-AS auto-discovery routes for these MVPNs, then
aggregation requires the ASBR 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 ASBR has not
previously advertised inter-AS auto-discovery routes for these
MVPNs, then the aggregation requires the ASBR to advertise (new)
inter-AS auto-discovery routes for these MVPN. The PMSI Tunnel
attribute in the newly advertised/re-advertised routes MUST carry
the identity of the P-Multicast tree that aggregates the MVPNs,
as well as an MPLS upstream assigned label [MPLS-UPSTREAM]. Each
re-advertised route MUST have a distinct label.
In addition the ASBR MUST send to the EBGP neighbor, from whom it
receives the inter-AS auto-discovery route, a BGP Update message that
carries a leaf auto-discovery route constructed 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 auto-discovery
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).
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+ The leaf auto-discovery 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 community by placing
the IP address carried in the next hop of the received inter-AS
auto-discovery 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
auto-discovery route to that community.
+ The Next Hop field of the MP_REACH_NLRI attribute of the route
SHOULD 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 auto-discovery route by the EBGP neighbor is
described in Section "Leaf auto-discovery route received via EBGP".
8.2.3.3. Leaf auto-discovery route received via EBGP
When an ASBR receives via EBGP a leaf auto-discovery route originated
by its neighbor ASBR, the ASBR accepts the route only if the Route
Target carried in the Extended Communities attribute of the route
matches one of the import Route Target configured on the ASBR.
If the ASBR accepts the leaf auto-discovery route, the ASBR finds an
inter-AS auto-discovery route whose MCAST-VPN NLRI has the same value
as the Route Key field of the the leaf auto-discovery route.
The MPLS label carried in the PMSI Tunnel attribute of the leaf auto-
discovery route is used to stitch a one hop ASBR-ASBR LSP to the tail
of the intra-AS tunnel segment associated with the found inter-AS
auto-discovery route.
8.2.3.4. Inter-AS auto-discovery 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.
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If a given inter-AS auto-discovery 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 auto-discovery 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 auto-discovery route, if (a)
at 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 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. The 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 auto-discovery route carries the PMSI Tunnel
attribute with the Tunnel Type set to LDP P2MP LSP, or PIM-SSM tree,
or PIM-SM tree, or PIM-Bidir tree, the PE/ASBR SHOULD join the P-
Multicast tree whose identity is carried in the Tunnel Identifier.
If the received inter-AS auto-discovery 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/ASBRas 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 auto-discovery route carries the PMSI Tunnel
attribute with the Tunnel Type set to LDP 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 auto-
discovery route and rooted at the AS that originated the inter-AS
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auto-discovery 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 received router is an
ASBR, this intra-AS segment may further be stitched to 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.
If the Leaf Information Required flag in the PMSI Tunnel attribute of
the received inter-AS auto-discovery route is set to 1, then the
PE/ASBR MUST originate a new leaf auto-discovery 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 auto-discovery
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).
+ If the received inter-AS auto-discovery route carries the PMSI
Tunnel attribute with the Tunnel Type set to Ingress Replication,
then the leaf auto-discovery 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 auto-discovery 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 auto-discovery route to that community.
+ The Next Hop field of the MP_REACH_NLRI attribute of the route
SHOULD 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 auto-discovery route is constructed, the PE/ASBR
advertises this route into IBGP.
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8.2.3.5. Leaf auto-discovery route received via IBGP
When an ASBR receives via IBGP a leaf auto-discovery route, the ASBR
accepts the route only if the Route Target carried in the Extended
Communities attribute of the route matches one of the import Route
Target configured on the ASBR.
If the ASBR accepts the leaf auto-discovery route, the ASBR finds an
inter-AS auto-discovery route whose MCAST-VPN NLRI has the same value
as the Route Key field of the the leaf auto-discovery route.
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 auto-
discovery route. The IP address of a leaf is the IP address carried
in the Originating Router's IP address field of the received leaf
auto-discovery 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. Non-congruent Unicast and Multicast Connectivity
If the multicast connectivity of a MVPN is congruent to its unicast
connectivity, the VRF of that MVPN, as referred to by this document,
means the VRF of that VPN used for unicast routing.
If the multicast connectivity of a MVPN is non-congruent to its
unicast connectivity, the VRF of that MVPN, as referred to by this
document, means the VRF that is distinct from the VRF of that VPN
used for unicast routing. On a given PE such a VRF may have its own
import and export Route Targets, different from the ones used by the
VRF used for unicast routing. These Route Targets are used to control
distribution of auto-discovery routes. In addition the export Route
Targets of the VRF are added to the Route Targets used for unicast
routing when originating (unicast) VPN-IP routes. The import Route
Targets associated with a given VRF are used to determine which of
the received (unicast) VPN-IP routes should be accepted into the VRF.
If an MVPN site is single-homed to a PE, then on this PE the VRF
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associated with the site SHOULD use the same RD as the one used by
the VRF used for unicast routing of that VPN. 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 VRF of the MVPN MUST
use its own distinct RD (although on a given PE the RD used by the
VRF of the MVPN SHOULD be the same as the one used by the VRF used
for unicast routing of that VPN).
Another non-congruency case is when all the the CE-PE routing for a
given MVPN uses BGP with Multiprotocol Extensions [RFC4760] with SAFI
2 "Network Layer Reachability Information used for multicast
forwarding" [IANA-SAFI] (and either IPv4 or IPv6 AFI). To handle this
case the routes that a PE receives from a CE over such SAFI are
placed in the VRF used by MVPN. Such routes are exchanged among PEs
using the same AFI as the one used for CE-PE routing information
exchange (either IPv4 or IPv6 AFI), and 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 [RFC 4364] 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 and
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 Section "Duplicate Packet Detection and
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Single Forwarder PE" of [MVPN].
10. VPN C-Multicast Routing Information Exchange 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.
10.1. 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).
10.1.1. Originating routes with 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.
10.1.1.1. Originating Source Tree Join C-multicast route
Whenever a PE creates a new <C-S,C-G> state in one of its MVPN-TIBs,
if C-S is reachable through some other PE the local PE originates 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.
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 PE deletes a previously created <C-S, C-G> state that had
resulted in originating a C-multicast route, the PE withdraws the
route (the withdrawn 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.
10.1.1.2. Originating Shared Tree Join C-multicast route
Whenever a PE creates a new <C-*, C-G> state in one of its MVPN-TIBs,
if the C-RP for C-G is reachable through some other PE the local PE
originates a C-multicast route of a type Shared Tree Join. The
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Multicast Source field in the MCAST-VPN NLRI of the route is set to
the C-RP address. The Multicast Group field in the MCAST-VPN NLRI is
set to the C-G address.
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 PE deletes a previously created <C-*, C-G> state that had
resulted in originating a C-multicast route, the PE withdraws the
route (the withdrawn route has the <C-*, C-G> Prune semantics). The
MCAST-VPN NLRI of the withdrawn route is carried in the
MP_UNREACH_NLRI attribute.
10.1.2. Originating routes with 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.
10.1.3. 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 uses its VRF to find (a) the autonomous system number
of the (remote) PE that originates the (unicast) route to the address
carried in the Multicast Source field of MCAST-VPN NLRI, and (b) the
import Route Target Extended Community associated with the VRF on the
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remote PE which was used to originate the route (the value of this
import Route Target is the value of the VRF Route Import Extended
Community carried in the unicast VPN-IP routing advertisements by the
remote PE). The Source AS field in the C-multicast route is set to
the found autonomous system. The Route Target Extended Community of
the C-multicast route is set to the found Route Target (the Route
Target constructed from the VRF Route Import).
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 an upstream PE to
reach that address are as specified in [MVPN].
If the local and the remote 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 remote PEs are in different ASes, then the local
PE finds in its VRF an inter-AS auto-discovery route whose Source AS
field carries the autonomous system number of the remote PE that
originates the (unicast) route to the address carried in the
Multicast Source field. The RD of the found inter-AS auto-discovery
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 auto-discovery 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.
Inter-AS auto-discovery routes are not used to support non-segmented
inter-AS tunnels. To support non-segmented inter-AS tunnels, if the
local and the remote PEs are in different ASes, the local system
finds in its VRF an intra-AS I-PMSI auto-discovery route whose
Originating Router's IP Address field 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
auto-discovery 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
auto-discovery route.
The Next Hop field of the MP_REACH_NLRI attribute is set to a
routable IP address of the local PE.
If the next hop of the found inter-AS auto-discovery 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 auto-
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discovery route is within the same AS as the local PE, then the PE
advertises the C-multicast route into IBGP.
10.1.4. Unicast Route Changes
Whenever unicast route used for determining PE connected to C-S/C-RP
changes, the local PE updates and re-originates the previously
originated C-multicast routes, as appropriate.
10.2. 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 import Route Targets configured on the ASBR, the ASBR finds an
inter-AS auto-discovery 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 discards the received C-multicast route.
Otherwise (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 auto-discovery route, the ASBR should match
it against the RD and the Originating Router's IP Addr of the (non-
segmented) inter-AS auto-discovery 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
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 withdrawn route.
Otherwise, the ASBR re-advertise the withdraw of a previously
advertised C-multicast route, as described below.
If the next hop for the found inter-AS auto-discovery route is an
EBGP neighbor of the ASBR, then the ASBR re-advertises the C-
multicast route to that neighbor. If the next hop for the found
inter-AS auto-discovery route is an IBGP neighbor of the ASBR, the
ASBR re-advertises the C-multicast route into IBGP. If it is the ASBR
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that originated the found inter-AS auto-discovery route in the first
place, then the ASBR just re-advertises the C-multicast route into
IBGP.
If the ASBR is the ASBR that originated the found inter-AS auto-
discovery 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 import Route Targets configured on the ASBR.
If the ASBR is not the ASBR that originating the found inter-AS auto-
discovery route, then before re-advertising the C-multicast route,
the ASBR modifies the Extended Communities attribute of the C-
multicast route as follows. If the Route Target of the route that
matches one of the import Route Targets configured on the ASBR is an
IP-based Route Target with the Global Administrator field set to the
IP address of ASBR, then the ASBR replaces this Route Target with a
newly constructed IP-based Route Target that has the Global
Administrator field set to the Next Hop of the found inter-AS auto-
discovery route, and Local Administrator field of this community set
to 0. 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.
10.3. 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 import Route Target
communities associated with the VRFs 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
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).
10.3.1. Receiving routes with 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).
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10.3.1.1. 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 there is no S-
PMSI for <C-S, C-G> then the PE adds an I-PMSI to the outgoing
interface list of the state if it is not already there. If there is
an S-PMSI for <C-S, C-G> then the PE add S-PMSI to the outgoing
interface list of the state if it is not already there.
10.3.1.2. 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. The PE
adds I-PMSI to the outgoing interface list of the state if it is not
already there.
10.3.2. Receiving routes with 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 LDP 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-Generic LSP Identifier Value.
If there is no S-PMSI for <C-Root Node Identifier, C-Generic LSP
Identifier Value> then the PE creates and advertises an S-PMSI as
described in Section "Switching to S-PMSI" using C-Root Node
Identifier as the value for the Multicast Source field of the S-PMSI
auto-discovery route and C-Generic LSP Identifier Value 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
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aggregated into a single P-Multicast tree (by using upstream assigned
labels).
10.4. 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 an other route with same NLRI.
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11. Switching to S-PMSI
[MVPN] describes a BGP based procedures for switching to S-PMSI. S-
PMSI auto-discovery routes are used for this purpose.
11.1. Originating S-PMSI auto-discovery routes
The following describes procedures for originating S-PMSI auto-
discovery routes by a PE.
An S-PMSI auto-discovery route instantiated for a given <C-S, C-G>
multicast stream is constructed as follows.
The MCAST-VPN NLRI of the route is constructed as follows.
+ The RD in this NLRI is set to the RD of the 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 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.
Depending on the type of a P-Multicast tree used to instantiate the
S-PMSI, the PMSI tunnel attribute of the S-PMSI auto-discovery route
is constructed as follows:
+ The PMSI tunnel attribute MUST contain the identity of the P-
Multicast tree that is used to instantiate the tunnel (note that
the PE could create the identity of the tree prior to the actual
instantiation of the tunnel). If in order to instantiate the
tunnel the PE needs to know the leaves of the tree within its own
AS, then the PE obtains this information from the leaf auto-
discovery routes received from other PEs/ASBRs within its own AS
(as other PEs/ASBRs originate leaf auto-discovery routes in
response to receiving the S-PMSI auto-discovery route) by setting
the Leaf Information Required flag in the PMSI Tunnel attribute
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to 1.
+ 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
auto-discovery 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
auto-discovery routes for these S-PMSIs, then the aggregation
requires the PE to advertise (new) S-PMSI auto-discovery 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 [MPLS-UPSTREAM]. If all these aggregated
S-PMSIs belong to the same MVPN, then the routes MAY carry an
MPLS upstream assigned label [MPLS-UPSTREAM]. The labels MUST be
distinct on a per MVPN basis, and MAY be distinct on a per route
basis.
The Next Hop field of the MP_REACH_NLRI attribute of the route SHOULD
be set to the same IP address as the one carried in the Originating
Router's IP Address field.
The route SHOULD carry the same set of Route Targets as the intra-AS
auto-discovery route of the MVPN originated by the PE.
11.2. Handling S-PMSI auto-discovery routes by ASBRs
Procedures for handling an S-PMSI auto-discovery 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 auto-discovery routes
the procedures apply to S-PMSI auto-discovery routes.
11.3. Receiving S-PMSI auto-discovery routes by PEs
Procedures for receiving an S-PMSI auto-discovery 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 auto-discovery route
received via IBGP" except that (a) instead of inter-AS auto-discovery
routes the procedures apply to S-PMSI auto-discovery routes, and (b)
a PE performs procedures specified in that section only if in
addition to the criteria specified in that section the PE has in its
MVPN-TIB the state for (C-S, C-G), where C-S is the Multicast Source
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and C-G is the Multicast Group carried in the S-PMSI auto-discovery
route, and the oif (outgoing interfaces) for this state contains one
or more interfaces to the locally attached CEs.
12. 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.
Use of RSVP-TE and/or BGP as the CE-PE multicast routing and label
distribution protocol is for further study.
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).
13. Choosing a single forwarder PE when switching from RPT to SPT
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.
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,
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.
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13.1. Source Within a Site - Source Active Advertisement
Whenever a PE creates an <C-S,C-G> state as a result of receiving a
Source Tree Join C-multicast route for <C-S, C-G> from some other PE,
the PE that creates the state MUST originate a Source Active auto-
discovery route. 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 route SHOULD carry the same set of Route Targets as the intra-AS
auto-discovery route of the MVPN originated by the PE.
Using the normal BGP procedures the Source Active auto-discovery
route is propagated to all the PEs of the MVPN.
Whenever the PE deletes the <C-S, C-G> state that was previously
created as a result of receiving a Source Tree Join C-multicast route
for <C-S, C-G> from some other PE, the PE that deletes the state MUST
also withdraw the Source Active auto-discovery route, if such a route
was advertised when the state was created.
13.2. Receiving Source Active auto-discovery route
When a PE receives a new Source Active auto-discovery 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 auto-discovery 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-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
auto-discovery routes. If there is one or more such matching routes,
and the best path to C-S carried in the matching route(s) is
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reachable through some other PE, then for each such route the PE MUST
originate a Source Tree Join C-multicast route.
When as a result of receiving a new Source Active auto-discovery
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 (auto-
discovery) 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.
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
auto-discovery 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 auto-discovery route).
A PE MUST withdraw a Source Tree Join C-multicast route for (C-S, C-
G) if the Source Active auto-discovery route that triggered the
advertisement of the C-multicast route is withdrawn.
13.2.1. Pruning Sources off the Shared Tree
If the incoming interface list (iif) for the found <C-*, C-G> entry
in the MVPN-TIB on the PE contains one of the PE-CE interfaces
(interfaces from the PE to its directly connected CEs), then the PE
MUST create in the MVPN-TIB a <C-S, C-G, RPT-bit> entry, if it does
not already exist. C-S of this entry is set to the address carried in
the Multicast Source field of the received Source Active auto-
discovery route, and C-G of this entry is set to the address carried
in the Multicast Group field of the route. Creating this entry
results in pruning <C-S, C-G> traffic off the shared (RPT) tree.
The PE maintains the <C-S, C-G, RPT-bit> entry for as long as it has
at least one Source Active auto-discovery route for <C-S, C-G>.
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14. Supporting PIM-SM without inter-site Shared 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.
14.1. Multicast Source Within a Site - Source Active Advertisement
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 auto-discovery 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:
+ 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.
The Multicast Source Length field is set appropriately to reflect
this.
+ The Multicast Group field MUST be set to the group address of the
multicast data packet carried in the PIM-Register message. The
Multicast Group Length field is set appropriately to reflect
this.
The route SHOULD carry the same set of Route Targets as the intra-AS
auto-discovery route of the MVPN originated by the PE.
Using the normal BGP procedures the Source Active auto-discovery
route is propagated to all the PEs of the MVPN.
When a PE that previously advertised a Source Active auto-discovery
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.
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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 auto-discovery 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 auto-discovery 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-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
auto-discovery 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 auto-discovery
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 (auto-
discovery) 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 (auto-discovery) 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
auto-discovery route.
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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 auto-discovery route).
A PE MUST withdraw a Source Tree Join C-multicast route for (C-S, C-
G) if the Source Active auto-discovery route that triggered the
advertisement of the C-multicast route is withdrawn.
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. 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 auto-discovery route originated by an ASBR aggregates
auto-discovery routes originated within the ASBR's own AS. Thus while
the auto-discovery routes originated within an AS are at the
granularity of <PE, MVPN> within that AS, outside of that AS the
(aggregated) inter-AS auto-discovery routes are at the granularity of
<AS, MVPN>. An inter-AS auto-discovery route for a given <AS, MVPN>
indicates the presence of or or more sites of the MVPN connected to
the PEs of the AS.
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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 auto-discovery routes 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. Dampening C-multicast routes
The rate of C-multicast routing changes advertised by a PE is not
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
removal of P2MP RSVP-TE leaves through advertisement/withdrawal of
leaf auto-discovery routes, will happen. Dampening techniques can be
used to limit corresponding processing.
To lessen the control plane overhead associated with processing of C-
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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. 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 only potential drawback of dampening of withdrawals of C-
multicast routes is that the PE that performs the dampening may
receive useless (multicast) traffic for some period of time. 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.
16.2. 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 is the
first for all the sites of the MVPN to do so.
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17. Dampening withdrawals of leaf auto-discovery routes
Similarly to the procedures proposed above for withdrawal of C-
multicast routes, dampening can be applied aggressively to the
withdrawal of leaf auto-discovery routes.
18. IANA Consideration
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.
19. Security Considerations
The mechanisms described in this document could re-use the existing
BGP security mechanisms.
20. Acknowledgement
Some of the text in Section "Supporting PIM-SM without inter-site
Shared Trees" has been taken almost verbatim from RFC3618.
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",
RFC1997, August 1996.
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[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 2858, 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
21.2. Informative References
[MPLS-UPSTREAM] R. Aggrwal, Y. Rekhter, E. Rosen, " MPLS Upstream
Label Assignment and Context Specific Label Space", draft-ietf-mpls-
upstream-label
[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
[RSVP-TE-P2MP] R. Aggarwal et. al., "Extensions to RSVP-TE for Point-
to-Multipoint TE LSPs", draft-ietf-mpls-rsvp-te-p2mp
[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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22. Author Information
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
Chaitanya Kodeboniya
23. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
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attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
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The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
24. Copyright Notice
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Raggarwa [Page 49]
