One document matched: draft-ietf-l3vpn-2547bis-mcast-bgp-00.txt
Network Working Group R. Aggarwal
Internet Draft Juniper Networks
Expiration Date: January 2007
E. Rosen
Cisco Systems, Inc.
T. Morin
France Telecom
Y. Rekhter
Juniper Networks
C. Kodeboniya
July 2006
BGP Encodings for Multicast in MPLS/BGP IP VPNs
draft-ietf-l3vpn-2547bis-mcast-bgp-00.txt
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Abstract
This document describes the BGP encodings for signaling 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 Terminology ........................................... 4
3 Introduction .......................................... 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 .................. 7
4.3 S-PMSI auto-discovery route ........................... 7
4.4 Leaf auto-discovery route ............................. 8
4.5 Source Active auto-discovery route (SA auto-discovery route) 9
4.6 C-Multicast Route ..................................... 9
5 P-Multicast Service Interface Tunnel (PMSI Tunnel) attribute 10
6 Source AS Extended Community .......................... 12
7 Route Import Extended Community ....................... 13
8 MVPN Auto-Discovery/Binding ........................... 14
8.1 MVPN Auto-Discovery/Binding - Intra-AS Operations ..... 14
8.1.1 Originating (intra-AS) auto-discovery routes .......... 14
8.1.2 Receiving (intra-AS) auto-discovery routes ............ 16
8.2 MVPN Auto-Discovery/Binding - Inter-AS Operations ..... 17
8.2.1 Originating Inter-AS MVPN Auto-Discovery routes ....... 18
8.2.2 Propagating Inter-AS MVPN Auto-Discovery routes ....... 19
8.2.2.1 Inter-AS Auto-Discovery Route received via EBGP ....... 20
8.2.2.2 Leaf Auto-Discovery Route received via EBGP ........... 22
8.2.2.3 Inter-AS Auto-Discovery Route received via IBGP ....... 22
8.2.2.4 Leaf Auto-Discovery route received via IBGP ........... 24
9 Non-congruent Unicast and Multicast Connectivity ...... 25
10 VPN C-Multicast Routing Information Exchange among PEs ....26
10.1 Originating C-Multicast Routes by a PE ................ 26
10.1.1 Constructing MCAST-VPN NLRI ........................... 26
10.1.1.1 PIM as the C-Multicast protocol ....................... 26
10.1.1.2 mLDP as the C-Multicast protocol ...................... 28
10.1.2 Constructing the rest of the C-multicast route ........ 29
10.1.3 Unicast Route Changes ................................. 29
10.2 Propagating C-Multicast routes by an ASBR ............. 29
10.3 Receiving C-Multicast Routes by a PE .................. 31
10.3.1 PIM as the C-Multicast protocol ....................... 31
10.3.1.1 Source Tree Join C-Multicast route .................... 31
10.3.1.2 Shared Tree Join C-Multicast route .................... 31
10.3.1.3 Prune Source from Shared Tree C-Multicast route ....... 32
10.3.2 mLDP as the C-Multicast protocol ...................... 32
10.4 C-multicast Routes Aggregation ........................ 32
11 Switching to S-PMSI ................................... 33
11.1 Originating S-PMSI auto-discovery routes .............. 33
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12 Carrier's Carrier ..................................... 35
13 Choosing a single forwarder PE when switching from RPT to SPT 35
13.1 Source Within a Site - Source Active Advertisement .... 35
13.2 Receiving Source Active auto-discovery route .......... 36
14 Co-locating C-RPs on a PE ............................. 37
14.1 Source Within a Site - Source Active Advertisement .... 37
14.2 Receiver(s) Within a Site ............................. 38
14.3 Receiving C-multicast routes .......................... 39
15 Scalability Considerations ............................ 39
16 Dampening of C-multicast routes ....................... 41
16.1 Dampening of C-multicast prunes ...................... 41
16.2 Dampening of C-multicast joins ........................ 42
16.3 Dampening of leaf auto-discovery routes ............... 42
17 IANA Consideration .................................... 42
18 Security Considerations ............................... 43
19 Acknowledgement ....................................... 43
20 References ............................................ 43
20.1 Normative References .................................. 43
20.2 Informative References ................................ 43
21 Author Information .................................... 44
22 Intellectual Property Statement ....................... 44
23 Copyright Notice ...................................... 45
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].
2. 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;
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+ S-PMSI auto-discovery route;
+ intra-AS segment leaf auto-discovery route (leaf auto-discovery
route);
+ Source Active auto-discovery route (SA 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;
+ Source Tree Join route;
+ Prune Source from Shared Tree 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 [PIM-SM], except
that instead of a single TIB a PE maintains multiple MVPN-TIBs, one
per each MVPN.
3. Introduction
This document describes the BGP encodings 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 - I-PMSI tunnel
binding, advertising <C-S, C-G> - 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 also specifies new BGP attribute, P-Multicast Service
Interface Tunnel (PMSI Tunnel) attribute.
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4. MCAST-VPN NLRI
This document defines a new BGP NLRI, called the MCAST-VPN NLRI.
This NLRI is carried in BGP using BGP Multiprotocol Extensions
[RFC2858]. Following is the format of the MCAST-VPN NLRI:
+-----------------------------------+
| Length (1 octet) |
+-----------------------------------+
| Route Type (1 octet) |
+-----------------------------------+
| Route Type specific (variable) |
+-----------------------------------+
The Length field indicates the length in octets of MCAST-VPN NLRI,
excluding the Length field itself.
The Route Type field defines encoding of the rest of MCAST-VPN NLRI
(Route Type specific 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 (or just SA auto-discovery
route).
This document defines the following Route Types for C-multicast
routes:
+ 6 - Shared Tree Join route;
+ 7 - Source Tree Join route;
+ 8 - Prune Source from Shared Tree route.
The following describes the format of the Route Type specific MCAST-
VPN NLRI for various Route Types defined in this document.
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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".
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) |
+-----------------------------------+
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| 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.
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.
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".
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4.5. Source Active auto-discovery route (SA auto-discovery route)
A Source Active (SA) 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 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.
Usage of Source Active auto-discovery routes is described in Sections
"Choosing a single forwarder PE when switching from RPT to SPT", and
"Co-locating C-RPs on a PE".
4.6. C-Multicast Route
A Shared Tree Join route, a Source Tree Join route, and a Prune
Source from Shared Tree route type specific MCAST-VPN NLRI have the
following encoding:
+-----------------------------------+
| RD (8 octets) |
+-----------------------------------+
| Source AS (4 octets) |
+-----------------------------------+
| Multicast Source Length (1 octet) |
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+-----------------------------------+
| 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.
If the Multicast Source field contains an IPv4 address, then the
value of the Multicast Source Length field is 32. If the Multicast
Source field contains an IPv6 address, then the value of the
Multicast Source Length field is 128.
The Multicast Source field contains the C-S 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.
Usage of C-multicast routes is described in Section "VPN C-Multicast
Routing Information Exchange among PEs".
The Group Address field contains the C-G address.
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:
+---------------------------------+
| Tunnel Type (2 octets) |
+---------------------------------+
| MPLS Label (3 octets) |
+---------------------------------+
| Tunnel Identifier (variable) |
+---------------------------------+
The Tunnel Type identifies the type of the tunneling technology used
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to establish the PMSI tunnel. The type determines the syntax and
semantics of the Tunnel Identifier field. This document defines the
following Tunnel Types:
+ 1 - Leaf Information Required
+ 2 - RSVP-TE P2MP LSP
+ 3 - LDP P2MP LSP
+ 4 - PIM-SSM Tree
+ 5 - PIM-SM Tree
+ 6 - PIM-Bidir Tree
+ 7 - Ingress Replication
+ 8 - 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 Leaf Information Required, the Tunnel
Identifier field is empty (zero length), and the MPLS Label field is
zero.
When the type is set to RSVP-TE P2MP LSP, the Tunnel Identifier
contains the RSVP-TE P2MP LSP's SESSION Object.
When the type is set to LDP P2MP LSP, the Tunnel Identifier is <P-
Root Node Address, Variable length opaque identifier>.
When the type is set to PIM-SM Tree, the Tunnel Identifier MUST
include <Sender Address, P-Multicast Group>, and MAY include P-RP
Node Address. 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.
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 Ingress Replication the Tunnel Identifier
carries the unicast tunnel endpoint.
When the type is set to LDP MP2MP LSP, the Tunnel Identifier is <P-
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Root Node Address, Variable length opaque identifier>.
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")
mandatory.
The PMSI Tunnel attribute is only 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 extended community called Source AS.
The Source AS is an AS specific extended community.
The Source AS extended community is of an extended type, and is
transitive across AS boundaries.
To support MVPN a PE that originates a (unicast) route to VPN-IPv4
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 SHOULD be set to 0.
Usage of the Source AS extended community is described in Sections
"PIM as the C-Multicast protocol", "mLDP as the C-Multicast
protocol", and "Receiving Source Active auto-discovery route".
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7. Route Import Extended Community
This document defines a new extended community called Route Import.
The Route Import is an IPv4 address specific extended community.
The Route Import is of an extended type, and is transitive across AS
boundaries.
To support MVPN in addition to the import/export Route Target(s) used
by the unicast routing, each VRF on a PE MUST have an import Route
Target that is unique to this VRF, 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 Route Target MUST be IP address
specific, and is constructed as follows:
+ The Global Administrator field of the Route Target MUST be set to
an IP address of the PE. This address MUST be a routable IP
address. This address MAY 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-IPv4 addresses MUST
include in the BGP Updates message that carries this route the 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 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 Route Import extended community is described in Sections
"PIM as the C-Multicast protocol", "mLDP as the C-Multicast
protocol", and "Receiving Source Active auto-discovery 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 [BGP-VPN]. 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 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 Route Import extended community of the VPN-IPv4 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
provider tunnel for the MVPN on the PE, the PMSI Tunnel attribute of
the intra-AS auto-discovery route is constructed as follows.
+ If a P-Multicast tree is used to instantiate the provider tunnel
for the MVPN on the PE, and either (a) this tree exists at the
time of discovery, or (b) the PE doesn't need to know the leaves
of the tree beforehand in order to advertise the P-Multicast tree
identifier, then the advertising PE SHOULD advertise the type and
the identity of the P-Multicast tree in the PMSI Tunnel attribute
of the route.
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+ If a P-Multicast tree is used to instantiate the provider tunnel
for the MVPN on the PE, and in order to advertise the P-Multicast
tree identifier the advertising PE needs to know the leaves of
the tree beforehand, the PE first discovers the leaves by
advertising an auto-discovery route without the PMSI Tunnel
attribute. Once the PE obtains the information about the leaves
(this information is obtained from the auto-discovery routes
received by the PE), the PE then advertises the binding of the
tree to the MVPN using the same route as the one used for the
auto-discovery, with the addition of carrying in the route the
PMSI Tunnel attribute that contains the type and the identity of
the P-Multicast tree. In other words, in the first phase the PE
advertises an auto-discovery route, but with no binding, and
receives auto-discovery routes from other PEs. Once this is
done, in the second phase the PE advertises binding based on the
information acquired in the first phase. If at some later point a
new PE advertises participation in the same MVPN, the initial
binding PMSI Tunnel binding information SHOULD NOT change (though
the leaves of the corresponding P-Multicast tree may change).
+ When the MVPN is aggregated with other MVPNs onto the same P-
Multicast tree, advertised in the PMSI Tunnel attribute, the PMSI
Tunnel attribute MUST carry a MPLS upstream assigned label [MPLS-
UPSTREAM] that is associated with the MVPN.
+ 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-IPv4 unicast routes. That is, by default the
auto-discovery route MUST carry the export Route Target used by the
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unicast routing. If any other PE has one of these Route Targets
configured for a VRF, it treats the advertising PE as a member in the
MVPN to which the VRF belongs. The default could be modified via
configuration by having a set of Route Targets used for the auto-
discovery routes being distinct from the ones used for the VPN-IPv4
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. 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, (c) the BGP route
selection determines that this is the best route with respect to the
NLRI carried by the route, and (d) the route carries the PMSI Tunnel
attribute, the PE performs the following.
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
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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.
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]).
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+ 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).
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 defined in this document.
Moreover, in addition to the above the ASBR performs the following
procedures.
8.2.1. Originating Inter-AS MVPN 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 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.
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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>.
8.2.2. Propagating Inter-AS MVPN 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. The
precise rules for distributing and processing the inter-AS auto-
discovery routes are given in subsequent sections.
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 neighbor" 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
constructed by its own independent mechanism. Moreover, by using
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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 following sections specify procedures for propagation of
(aggregated) inter-AS auto-discovery routes across ASes.
8.2.2.1. 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.
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.
Depending on the type of a P-Multicast tree used to instantiate the
intra-AS segment of the inter-AS tunnel, the PMSI Tunnel attribute of
the re-advertised inter-AS auto-discovery route is constructed as
follows:
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+ If the ASBR uses ingress replication to instantiate the intra-AS
segment of the inter-AS tunnel, the re-advertised route SHOULD
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, and in order to advertise the P-
Multicast tree identifier the ASBR does not need to know the
leaves of the tree beforehand, then the advertising ASBR SHOULD
advertise the type and the identity of the P-Multicast tree in
the PMSI Tunnel attribute of the route. This, in effect, creates
a binding between the inter-AS auto-discovery route and the P-
Multicast tree.
+ If the ASBR uses a P-Multicast tree to instantiate the intra-AS
segment of the inter-AS tunnel, and in order to advertise the P-
Multicast tree identifier the advertising ASBR needs to know the
leaves of the tree beforehand, the inter-AS auto-discovery route
re-advertised by the ASBR MUST include the PMSI Tunnel attribute
with the Tunnel Type set to Leaf Information Required. As a
result the ASBR first discovers the leaves using the procedures
specified in "Leaf Auto-Discovery route received via IBGP". The
ASBR then advertises the binding of the tree to the inter-AS
auto-discovery route using the original inter-AS auto-discovery
route, with the addition of carrying in the route the PMSI Tunnel
attribute that contains the type and the identity of the tree. In
other words, in the first phase the ASBR advertises inter-AS
auto-discovery routes, but with no binding. Once this is done, in
the second phase the ASBR advertises binding based on the
information acquired in the first phase.
+ When multiple inter-AS auto-discovery routes are bound onto the
same P-Multicast tree advertised in the PMSI Tunnel attribute,
the PMSI Tunnel attribute MUST carry a MPLS upstream assigned
label [MPLS-UPSTREAM] that is associated with the inter-AS auto-
discovery route.
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 to demultiplex the
MVPN traffic received over a unicast tunnel by the advertising
router.
+ 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 Community 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]).
8.2.2.2. Leaf Auto-Discovery Route received via EBGP
When an ASBR receives via EBGP a leaf auto-discovery route, the ASBR
accepts the route only if the Route Target carried in the Extended
Community 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.
8.2.2.3. 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.
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
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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.
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
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 Tunnel Type in the PMSI Tunnel attribute of the received
inter-AS auto-discovery route is set to either Leaf Information
Required or Ingress Replication, then the PE/ASBR originates a new
leaf auto-discovery route as follows.
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+ The route carries a single MCAST-VPN NLRI with the Route Key
field set to the MCAST-VPN NLRI of the inter-AS 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 Community 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.
8.2.2.4. 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
Community 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.
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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 for the
auto-discovery routes. The export Route Targets are added to the
Route Targets used for unicast routing when originating VPN-IPv4
routes. The export Route Targets control the set of sites that could
receive multicast traffic originated by the sources within the local
site. The import Route Targets associated with a given VRF are used
to determine which of the received VPN-IPv4 routes should be accepted
into the VRF. The import Route Targets control the set of sites that
contain sources of multicast traffic that could be received within
the local site.
If an MVPN site is single-homed to a PE, then on this PE the VRF
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
should 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).
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,
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unless either (a) some other PEs that have VRFs in that MVPN use RSVP
TE P2MP LSPs, 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, in which case the PE
originates an auto-discovery route with the PMSI Tunnel attribute
indicating ingress replication.
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
10.1.1. Constructing MCAST-VPN NLRI
Procedures for constructing MCAST-VPN NLRI depend on the multicast
routing protocol between CE and PE (C-multicast protocol).
10.1.1.1. 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> or <C-S, C-G, RPT-bit> or <C-*, C-*> state learnt by a
PE via the C-multicast protocol.
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. 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 MCAST-VPN NLRI is carried as a Source Tree Join route type. 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.
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. The Multicast Source field in the
MCAST-VPN NLRI of the route is set to the C-RP address. The Multicast
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Group field in the MCAST-VPN NLRI is set to the C-G address. The
MCAST-VPN NLRI of the route is carried as the Shared Tree Join route
type. 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.
Whenever a PE creates a new <C-S, C-G, RPT-bit> state in one of its
MVPN-TIBs, except for the case when this state is created when the PE
that has an existing <C-*, C-G> state switches from the C-RP based
tree to the C-S based tree for C-G, if the C-RP is reachable through
some other PE, the local PE originates a C-multicast route. The
Multicast Source field in the MCAST-VPN NLRI of the route is set to
C-S, and the Multicast Group field is set to C-G. The MCAST-VPN NLRI
of the route is carried as the Prune Source from Shared Tree route
type. The semantics of the route is to indicate that the receivers
for <C-S,C-G> no longer want to receive <C-S, C-G> traffic via the C-
RP based tree (the route has the <C-S,C-G, RPT> Prune semantics). If
later on the PE deletes a previously created <C-S, C-G, RPT-bit>
state, the PE withdraws the route (the semantics of the withdrawn
route is to indicate that <C-S, C-G> traffic should be carried via
the C-RP-based tree). The MCAST-VPN NLRI of the withdrawn route is
carried in the MP_UNREACH_NLRI attribute.
Whenever a PE creates a <C-*, C-*> state in one of its MVPN-TIBs, if
the C-RP is reachable through some other PE the local PE originates a
C-multicast route. The Multicast Source field in the MCAST-VPN NLRI
of the route is set to the C-RP address. The Multicast Group field in
the NLRI MUST be set to a wildcard i.e. 0. The MCAST-VPN NLRI of the
route is carried as the Shared Tree Join route type. Whenever a PE
deletes a previously created <C-*, C-*> state that had resulted in
originating a C-multicast route, the PE withdraws the route (the
withdrawn route has the (C-*, C-*) Prune semantics). The MCAST-VPN
NLRI of the withdrawn route is carried in the MP_UNREACH_NLRI
attribute.
The (local) PE uses its VRF to determine (a) the autonomous system
number of the (remote) PE that originates the (unicast) route to C-
S/C-RP, and (b) the import Route Target community associated with the
VRF on the remote PE which was used to originate the route (this
information is available from the Route Import extended community
carried in the unicast VPN-IPv4 routing advertisements by the remote
PE). Note that for a C-multicast route that the PE originates in
response to creating a <C-S, C-G, RPT-bit> state, the remote PE is
the PE that originates the route to C-RP, not to C-S. The Source AS
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field in the C-multicast route is set to the found autonomous system.
The Extended Community attribute of the C-multicast route is set to
the found Route Target.
If there is more than one (remote) PE that originates the (unicast)
route to C-S/C-RP, then the procedures for selecting an upstream PE
to reach C-S/C-RP are as specified in [MVPN].
10.1.1.2. 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
as follows:
+ The PE constructs MCAST-VPN NLRI of the route by placing X into
the Multicast Source field, and placing Y into the Multicast
Group field.
+ The PE uses its VRF to determine (a) the autonomous system number
of the (remote) PE that originates the (unicast) VPN-IPv4 route
to X, and (b) the import Route Target community associated with
the VRF on the remote PE which was used to originate the route
(this information is available from the Route Import extended
community carried in the unicast VPN-IPv4 routing advertisements
by the remote PE). The Source AS field in the C-multicast route
is set to the found autonomous system. The Extended Community
attribute of the C-multicast route is set to the found Route
Target.
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.
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10.1.2. 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).
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-IPv4 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 Community attribute of the C-multicast 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-
discovery route is within the same AS as the local PE, then the PE
advertises the C-multicast route into IBGP.
10.1.3. 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 PE discards the received C-multicast route. Otherwise
(if a matching route is found) the PE proceeds as follows.
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When an ASBR receives a BGP Update message that carries a C-multicast
route, 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 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
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.
Unless it is the ASBR that originating the found inter-AS auto-
discovery route in the first place, then before re-advertising the C-
multicast route, the ASBR modifies the Extended Community 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 Community attribute of the route
SHOULD be passed unmodified.
The Next Hop field of the MP_REACH_NLRI attribute SHOULD be set to a
routable IP address of the ASBR.
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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 Community 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-IPv4 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.
Procedures for a PE to process received C-multicast routes depend on
the multicast routing protocol between CE and PE (C-multicast
protocol).
10.3.1. 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).
10.3.1.1. 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. 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.
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10.3.1.3. Prune Source from Shared Tree C-Multicast route
If the received route has the route type set to Prune Source from
Shared Tree, then the PE creates a new <C-S, C-G, RPT-bit> 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.
10.3.2. 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
creates a new <X, Y> 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 <X, Y>
then the PE creates and advertises an S-PMSI for <X, Y>, as described
in section "Switching to S-PMSI". If there is an S-PMSI for <X, Y>
then the PE add S-PMSI to the outgoing interface list of the state if
it is not already there.
10.4. C-multicast Routes Aggregation
Note that C-multicast routes are "de facto" aggregated by BGP. The
MCAST-VPN NLRIs advertised by multiple PEs, for a C-multicast route,
for a particular MVPN, C-S and C-G, 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.
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This also implies that an ASBR aggregates all the received C-
multicast routes for a given (S,G) of a given MVPN into a single C-
multicast route.
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 the 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.
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.
Procedures for handling an S-PMSI auto-discovery route outside of the
autonomous system of the PE that originates the route are the same as
specified in "Propagating Inter-AS MVPN Auto-Discovery Information",
except that instead of inter-AS auto-discovery routes the procedures
apply to S-PMSI auto-discovery routes.
Procedures for receiving an S-PMSI auto-discovery route by a PE
within the same autonomous system as the PE that originates the route
are the same as specified in "Inter-AS Auto-Discovery Route received
via IBGP", except that instead of inter-AS auto-discovery routes the
procedures apply to S-PMSI auto-discovery routes.
The following describes procedures for originating S-PMSI auto-
discovery routes by a PE.
11.1. Originating S-PMSI auto-discovery routes
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.
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+ 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 Route Import extended community of the VPN-IPv4 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:
+ If a P-Multicast tree is used to instantiate the S-PMSI, and in
order to advertise the P-Multicast tree identifier the PE does
not need to know the leaves of the tree within its own AS
beforehand, then the advertising PE SHOULD advertise the type and
the identity of the P-Multicast tree in the PMSI Tunnel attribute
of the route. This, in effect, creates a binding between the S-
PMSI auto-discovery route and the P-Multicast tree.
+ If a P-Multicast tree is used to instantiate the S-PMSI, and in
order to advertise the P-Multicast tree identifier the
advertising PE needs to know the leaves of the tree within its
own AS beforehand, the S-PMSI auto-discovery route advertised by
the PE MUST include the PMSI Tunnel attribute with the Tunnel
Type set to Leaf Information Required. As a result the PE first
discovers the leaves using the procedures specified in "Leaf
Auto-Discovery route received via IBGP", except that instead of
inter-AS auto-discovery routes the procedures applied to S-PMSI
auto-discovery routes. The PE then advertises the binding of the
P-Multicast tree to the S-PMSI auto-discovery route using the
original S-PMSI auto-discovery route with the addition of
carrying in the route the PMSI Tunnel attribute that contains the
type and the identity of the tree. In other words, in the first
phase the PE advertises an S-PMSI auto-discovery route, but with
no binding. Once this is done, in the second phase the PE
advertises binding based on the information acquired in the first
phase.
+ When within a given AS multiple S-PMSI auto-discovery routes are
bound onto the same P-Multicast tree advertised in the PMSI
Tunnel attribute, the PMSI Tunnel attribute MUST carry an MPLS
upstream assigned label [MPLS- UPSTREAM] that is associated with
the individual S-PMSI auto-discovery route.
The Next Hop field of the MP_REACH_NLRI attribute of the route SHOULD
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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
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 strongly 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
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 consistant 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.
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 SHOULD originate a Source Active auto-
discovery route. The route carries a single MCAST-VPN NLRI
constructed as follows:
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+ The RD in this NLRI is set to the RD of the VRF of the MVPN on
the PE.
+ The Multicast Source field MUST be set to 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 previousely
created as a result of receiving a C-multicast route for <C-S, C-G>
from some other PE, the PE that deletes the state also withdraws 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 that
carries a given <C-S, C-G>, the PE finds a VRF whose import Route
Targets match one or more of the Route Targets carried by the route.
The PE then checks for an <*, C-G> or an <C-S, C-G> entry in that VRF
with a non-empty outgoing interface list that contains one or more
PE-CE interfaces (interfaces from the PE to its directly connected
CEs). Presence of such an entry implies that some system in the sites
(directly) connected to the PE is interested in the <C-S, C-G>
carried in the Source Active auto-discovery route, in which case the
PE originates a Source Tree Join C-multicast route for <C-S, C-G>.
If a PE receives from one of its directly connected CEs a PIM Join
message for a new group C-G, the PE SHOULD originate a Source Tree
Join C-multicast route for each Source Active auto-discovery route
that contains C-G and is present in the VRF associated with the CE.
Construction and distribution of the Source Tree Join C-multicast
route follows the procedures specified in "VPN C-Multicast Routing
Information Exchange among PEs", except that procedures specified in
"Constructing MCAST-VPN NLRI" are replaced with the following:
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+ The Multicast Source Length, Multicast Source, Multicast Group
Length, and Multicast Group fields are copied from the
corresponding field in the Source Active auto-discovery route.
+ The (local) PE uses its VRF to find (a) the autonomous system
number of the (remote) PE that originates the (unicast) route to
C-S carried in the Multicast Source field of the Source Active
auto-discovery route, and (b) the import Route Target community
associated with the VRF on the remote PE which was used to
originate the (unicast) route (this information is available from
the Route Import extended community carried in the unicast VPN-
IPv4 routing advertisements by the remote PE). The Source AS
field in the C-multicast route is set to the found autonomous
system. The Extended Community attribute of the C-multicast route
is set to the found Route Target.
If there is more than one (remote) PE that originates the
(unicast) route to C-S, then the procedures for selecting an
upstream PE to reach C-S are as specified in [MVPN].
If the incoming interface list (iif) for the <*, C-G> state 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 creates in
the MVPN-TIB a <C-S, C-G, RPT-bit> state, if it does not already
exist. C-S of this state is set to the address carried in the
Multicast Source field of the Source Active auto-discovery route, and
C-G of this state is set to the address carried in the Multicast
Group field of the route. Creating this state results in pruning <C-
S, C-G> traffic off the shared (RPT) tree.
14. Co-locating C-RPs on a PE
This section describes the procedures for co-locating a C-RP on a PE.
The procedures are for the anycast RP based on C-(*, G) scheme
described in [MVPN].
14.1. Source Within a Site - Source Active Advertisement
When a PE that acts as an anycast RP for a given MVPN first learns of
a new (multicast) sender within that MVPN, e.g., via PIM register
messages originated within that MVPN, the PE follows the normal PIM
procedures. In addition, 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:
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+ The RD in this NLRI is set to the RD of the VRF of the MVPN on
the PE.
+ The Multicast Source field MUST be set to the source IP address
of the multicast data packet carried in the PIM-Register message.
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 previousely advertised a Source Active auto-discovery
route for a given sender learns that the sender is no longer active
the PE withdraws the previously advertised Source Active route.
14.2. Receiver(s) Within a Site
When a PE receives a new Source Active auto-discovery route that
carries a given <C-S, C-G>, the PE finds a VRF whose import Route
Targets match one or more of the Route Targets carried by the route.
The PE then checks for an <*, C-G> or an <C-S, C-G> entry in that VRF
with a non-empty outgoing interface list that contains one or more
PE-CE interfaces (interfaces from the PE to its directly connected
CEs). Presence of such an entry implies that some system in the sites
(directly) connected to the PE is interested in the <C-S, C-G>
carried in the Source Active auto-discovery route, in which case the
PE originates a Source Tree Join C-multicast route for <C-S, C-G>.
If a PE receives from one of its directly connected CEs a PIM Join
message for a new group C-G, the PE SHOULD originate a Source Tree
Join C-multicast route for each Source Active auto-discovery route
that contains C-G and is present in the VRF associated with the CE.
Construction and distribution of the Source Tree Join C-multicast
route follows the procedures specified in "VPN C-Multicast Routing
Information Exchange among PEs", except that procedures specified in
"Constructing MCAST-VPN NLRI" are replaced with the following:
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+ The Multicast Source Length, Multicast Source, Multicast Group
Length, and Multicast Group fields are copied from the
corresponding field in the Source Active auto-discovery route.
+ The (local) PE uses its VRF to find (a) the autonomous system
number of the (remote) PE that originates the (unicast) route to
C-S carried in the Multicast Source field of the Source Active
auto-discovery route, and (b) the import Route Target community
associated with the VRF on the remote PE which was used to
originate the (unicast) route (this information is available from
the Route Import extended community carried in the unicast VPN-
IPv4 routing advertisements by the remote PE). The Source AS
field in the C-multicast route is set to the found autonomous
system. The Extended Community attribute of the C-multicast route
is set to the found Route Target.
If there is more than one (remote) PE that originates the
(unicast) route to C-S, then the procedures for selecting an
upstream PE to reach C-S are as specified in [MVPN].
A PE which receives C-Join for <C-*, C-G> or <C-S, C-G> from one of
its connected CEs that belong to a given MVPN does not send the
information that it has receiver(s) for C-G until it receives an
Source Active auto-discovery route from some other PE indicating that
there are active sources for that C-G.
14.3. Receiving C-multicast routes
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 "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 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]).
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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.
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-IPv4 routes (although they may be
used for VPN-IPv4 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.
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16. Dampening of 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-
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 of C-multicast prunes
A PE/ASBR/Route Reflector can OPTIONALLY delay the advertisement of
C-multicast prune routes (routes resulting from the removal of
multicast state). 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 C-multicast prune 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 C-multicast prune 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
C-multicast prune routes due to the use of I-PMSIs.
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16.2. Dampening of C-multicast joins
A PE/ASBR/Route Reflector can OPTIONALLY delay the advertisement of
C-multicast join routes (routes resulting from the creation of
multicast state). 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 C-multicast join routes will not impede multicast join
latency observed by a given MVPN, except if the PE advertising the C-
multicast join route is the first for all the sites of the MVPN to do
so.
16.3. Dampening of leaf auto-discovery routes
As described in section "Switching to S-PMSI, leaf auto-discovery
routes are used for S-PMSI tunnel for which the root need to know the
leaves of the tree.
Similarly to the procedures proposed above for C-multicast routes,
dampening can be applied aggressively to the withdrawal of such auto-
discovery routes.
17. 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 Route
Import. This community is IPv4 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 is assigned its own SAFI.
This document defines a new BGP optional transitive attribute, called
PMSI Tunnel.
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18. Security Considerations
The mechanisms described in this document could re-use the existing
BGP security mechanisms.
19. Acknowledgement
Some of the text in Section "Co-locating C-RPs on a PE" has been
taken almost verbatim from RFC3618.
20. References
20.1. Normative References
[MVPN] E. Rosen, R. Aggarwal [Editors], "Multicast in MPLS/BGP IP
VPNs", draft-ietf-l3vpn-2547bis-mcast-01.txt,
[RFC2119] "Key words for use in RFCs to Indicate Requirement
Levels.", Bradner, March 1997
[RFC2858] Bates, T., Rekhter, Y., Chandra, R., and D. Katz,
"Multiprotocol Extensions for BGP-4", RFC 2858, June 2000.
[RFC4364] E. Rosen, Y. Rekhter, "BGP/MPLS IP Virtual Private Networks
(VPNs)", RFC4364, February 2006
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, February 2006.
20.2. Informative References
[MPLS-UPSTREAM] R. Aggrwal, Y. Rekhter, E. Rosen, " MPLS Upstream
Label Assignment and Context Specific Label Space", draft-ietf-mpls-
upstream-label-00.txt
[PIM-SM] B. Fenner et. al., "Protocol Independent Multicast - Sparse
Mode (PIM-SM): Protocol Specification (Revised)", draft-ietf-pim-sm-
v2-new-11.txt
[RT-CONSTRAIN] P. Marques et. al., ",Constrained VPN Route
Distribution" draft-ietf-l3vpn-rt-constrain-02
[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-00
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21. 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
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23. Copyright Notice
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This document is subject to the rights, licenses and restrictions
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This document and the information contained herein are provided on an
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Raggarwa [Page 45]
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