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 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Raggarwa [Page 1] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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]. Raggarwa [Page 2] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 Raggarwa [Page 3] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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]. Raggarwa [Page 4] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 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; Raggarwa [Page 5] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 + 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: Raggarwa [Page 6] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 + 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". Raggarwa [Page 7] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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. Raggarwa [Page 8] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 Raggarwa [Page 9] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 Raggarwa [Page 10] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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: Raggarwa [Page 11] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 + 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 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 , as carried in the P2MP FEC [mLDP]. When the type is set to PIM-SM Tree, the Tunnel Identifier is . 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 . 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 . 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. Raggarwa [Page 12] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 , 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". Raggarwa [Page 13] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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". Raggarwa [Page 14] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 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 Raggarwa [Page 15] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 Raggarwa [Page 16] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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: Raggarwa [Page 17] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 + 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. Raggarwa [Page 18] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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). Raggarwa [Page 19] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 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 within that AS, outside of that AS the (aggregated) inter-AS auto-discovery routes could be at the granularity of . Raggarwa [Page 20] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 Raggarwa [Page 21] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 , 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 Raggarwa [Page 22] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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). Raggarwa [Page 23] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 + 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. Raggarwa [Page 24] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 Raggarwa [Page 25] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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. Raggarwa [Page 26] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 Raggarwa [Page 27] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 Raggarwa [Page 28] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 , or 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 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 in the sites connected to the PE (the route has the Join semantics). Whenever a PE deletes a previously created state that had resulted in originating a C-multicast route, the PE withdraws the route (the withdrawn route has the 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 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 Raggarwa [Page 29] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 in the sites connected to the PE (the route has the Join semantics). Whenever a PE deletes a previously created state that had resulted in originating a C-multicast route, the PE withdraws the route (the withdrawn route has the 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 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 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 to the forwarding state associated with . If the PE does not have state for 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 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 Raggarwa [Page 30] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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- Raggarwa [Page 31] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 Raggarwa [Page 32] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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). Raggarwa [Page 33] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 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 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 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 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 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 Raggarwa [Page 34] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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. Raggarwa [Page 35] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 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 . + 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 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 Raggarwa [Page 36] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 Raggarwa [Page 37] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 and have chosen a consistent upstream PE, as described in [MVPN], for state. Further this upstream PE, say PE1, is using an MI-PMSI for . If a site attached to one of these PEs, say PE2, switches to the C-S tree for , 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 , as PE1 uses for . This results in {PE2, PE4, PE6} receiving duplicate traffic for - 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 . The following describes how this is achieved. Raggarwa [Page 38] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 13.1. Source Within a Site - Source Active Advertisement Whenever a PE creates an state as a result of receiving a Source Tree Join C-multicast route for 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 state that was previously created as a result of receiving a Source Tree Join C-multicast route for 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 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) 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 Raggarwa [Page 39] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 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 upstream state in one of its MVPN-TIBs, but has no 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 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 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 traffic off the shared (RPT) tree. The PE maintains the entry for as long as it has at least one Source Active auto-discovery route for . Raggarwa [Page 40] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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. Raggarwa [Page 41] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 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) 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 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. Raggarwa [Page 42] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 upstream state in one of its MVPN-TIBs, but has no 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 within that AS, outside of that AS the (aggregated) inter-AS auto-discovery routes are at the granularity of . An inter-AS auto-discovery route for a given indicates the presence of or or more sites of the MVPN connected to the PEs of the AS. Raggarwa [Page 43] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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 , 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 Join originated within a site, all the subsequent Joins for same 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- Raggarwa [Page 44] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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. Raggarwa [Page 45] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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. Raggarwa [Page 46] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 [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 Raggarwa [Page 47] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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. 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Raggarwa [Page 48] Internet Draft draft-ietf-l3vpn-2547bis-mcast-bgp-03.txt July 2007 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]