transmitted more than once by the PE. Similarly, if the PMSI is instantiated by IR, each packet may be transmitted multiple times. It is still the case, though, that the packet is transmitted only on one PMSI. This document provides procedures for supporting this transmission model using either BGP or PIM as the PE-PE C-multicast control protocol. There are two variants of this transmission model: "without extranet separation" and "with extranet separation". Section 2.1. By definition, when extranet separation is used, the following rule MUST be applied: Traffic from extranet C-sources MUST NOT be carried in the same P-tunnel as traffic from non-extranet C-sources. This rule does not impact those VRFs that contain only non-extranet C-sources, nor does it impact those VRFs that contain only extranet C-sources. However, if a particular VRF contains both kinds of C-sources, it will need to advertise some P-tunnels that are used for carrying only extranet C-flows and some that are used only for carrying non-extranet C-flows. This document provides procedures for supporting extranet separation when BGP is used as the PE-PE C-multicast control protocol. Support for extranet separation using PIM as the PE-PE C-multicast control protocol is outside the scope of this document.
Section 5.1 of [RFC6513], in order for a C-flow (C-S,C-G) to be carried across the SP backbone, a VRF that has multicast receivers for that C-flow must import a route that matches C-S, and this route must be "eligible for UMH selection". In this document, we will refer to these routes as "UMH-eligible extranet C-source routes". The UMH-eligible extranet C-source routes do not necessarily have to be unicast routes; they MAY be SAFI 129 routes (see Section 5.1.1 of [RFC6513]). For example, suppose that one wants a VPN-R C-receiver to be able to receive extranet C-flows from C-sources in VPN-S but does not want any VPN-R system to be able to send unicast traffic to those C-sources. One can achieve this by using SAFI 129 routes as the UMH-eligible routes exported from VPN-S and imported by VPN-R. Since SAFI 129 routes are used only for UMH determination and not for unicast routing, this allows the multicast traffic to be forwarded properly but does not create unicast routes to the C-sources. If a customer is using PIM-SM in the ASM model and one or more customer sites have C-receivers that are allowed by policy to join a (C-*,C-G) tree, where C-G is an extranet C-group, then any VRF with C-receivers for that group MUST import a UMH-eligible route that matches C-RP, where C-RP is the Rendezvous Point (RP) address for C-G. The UMH-eligible extranet C-source and C-RP routes do not have to be "host routes". That is, they can be routes whose IPv4 address prefixes are not 32 bits in length or whose IPv6 address prefixes are not 128 bits in length. So, it is possible for a UMH-eligible
extranet C-source route to match the address of an extranet C-source and to also match the address of a non-extranet C-source. However, if such a route is exported from a VPN-S VRF and imported by a VPN-R VRF, VPN-R receivers will be able to receive C-flows from any non-extranet C-sources whose addresses match that route. To prevent this, the VPN-S VRF SHOULD be provisioned such that it will NOT export a UMH-eligible route that matches (in the context of the VPN-R VRF) both extranet C-sources and non-extranet C-sources. Failure to follow this rule may result in a VPN security violation. (See Section 10.) In general, one does not want ALL the routes from the VPN-S VRFs to be exported to all the VPN-R VRFs, as only a subset of the routes in the VPN-S VRFs will be UMH-eligible extranet C-source routes. Route distribution is, as is always the case for a BGP/MPLS IP VPN [RFC4364], controlled by Route Targets (RTs). A variety of route distribution policies can be created by appropriately provisioning the import and export RTs of the various VRFs. For example, the VPN-S VRFs that contain extranet C-sources could be configured to apply an export RT whose value is "RT-A-extranet" to the routes that match the extranet C-sources. The VPN-R VRFs that contain extranet C-receivers allowed to receive extranet C-flows from VPN-S extranet C-sources could then be configured with "RT-A-extranet" as an import RT. Arbitrarily complex policies can be created by suitable manipulation of the import and export RTs.
RFC7761], o The "first-hop designated router (DR)" for C-S needs to be able to unicast PIM Register messages to a C-RP that services C-G. o The C-RPs servicing C-G need to be able to unicast PIM Register-Stop messages to the DR for C-S. It follows that if a VRF contains C-S but does not contain a C-RP for C-G, then the VRF MUST import a unicast route matching a C-RP for C-G. Note that the unicast route matching the C-RP is needed whether or not the VRF has also imported a SAFI 129 route matching the C-RP. (If the VRF also contains receivers for C-G and UMH determination is being done using SAFI 129 routes, both a unicast route and a SAFI 129 matching C-RP route are needed.) Similarly, if a VRF contains a C-RP for C-G but does not contain C-S, the VRF MUST import a unicast route matching the DR for C-S. Note that the unicast route matching the DR for C-S is needed even if UMH determination is being done using SAFI 129 routes; in that case, if the VRF also contains receivers for C-G, it needs to import a SAFI 129 route matching C-S and a unicast route matching the DR for C-S. If, for a particular extranet C-group, C-G, the customer is using "anycast-RP" [RFC3446] [RFC4610] or the Multicast Source Discovery Protocol (MSDP) [RFC3618], then all the C-RPs serving C-G need to send unicast messages to each other. Thus, any VRF that contains a C-RP for C-G needs to import unicast routes matching ALL the other C-RPs that serve C-G. The need to distribute these unicast routes is usually not a problem as long as all the C-sources and C-RPs for C-G are in the same MVPN. If, however, the C-sources are not all in the same MVPN, great care must be taken to ensure that the unicast routes mentioned above are properly distributed. There may be scenarios in which all the C-sources for C-G are in the same MVPN, but there are receivers in different VPNs, and some or all of the VPNs with receivers have their own C-RPs for C-G. In this case, care must be taken to ensure that the C-RPs can all unicast to each other.
Section 2.2 is possible. (The conditions under which such ambiguity is possible are also described in Section 2.2.) We want to ensure that, in any given VRF, the UMH-eligible route matching a given extranet C-source has an RT in common with every BGP A-D route that advertises a P-tunnel that may be used to carry extranet multicast traffic from that C-source. We also want to ensure that the UMH-eligible route matching a given extranet C-source does not have any RT in common with any BGP A-D route that advertises a P-tunnel that may be used to carry any multicast traffic from a different C-source that has the same IP address. This enables us to determine whether traffic that appears to be from the given C-source is really arriving on the wrong P-tunnel and hence is really from a different C-source with the same IP address. Suppose that an IP address C-S is used in VPN-A as the address of one system and used in VPN-B as the address of a different system. In this case, one or more VPN-A VRFs may export a VPN-IP route whose NLRI is <RD1,S>, and one or more VPN-B VRFs may export a VPN-IP route whose NLRI is <RD2,S>, where RD1 != RD2. Consider two routes -- R1 and R2 -- for which the following conditions all hold: o R1 and R2 are UMH-eligible extranet C-source or C-RP routes, or are unicast routes matching a C-RP. o R1 is exported from a VRF of VPN-A, while R2 is exported from a VRF of a different VPN, say VPN-B. o R1's NLRI specifies IP address prefix S/n. o R2's NLRI specifies IP address prefix S/m. o m >= n (S/m is either the same as or more specific than S/n). o There is some host address H such that: * H denotes a different system in VPN-A than in VPN-B, and * H/m == S/m (so either S/m or S/n might be a longest match for H in some VRF).
We impose the following constraint: RTs MUST be assigned in such a way that R1 and R2 do not have any RT in common. (This constraint is not as onerous as it may seem. Typically, R1 and R2 would not have an RT in common, as that might result in their being imported into the same VRF, making the address H ambiguous in that VRF.) Sections 6 and 7 specify procedures for determining if a received C-flow has been received over the expected P-tunnel. Those procedures will not work if this constraint is violated. (The constraint described in this section is necessary, but not sufficient, for the procedures of Sections 6 and 7 to work; additional constraints that cover the assignment of RTs to BGP A-D routes are given in subsequent sections.) Sections 4.1, 4.2, and 4.3 place specific requirements on the way in which certain VPN-IP routes are distributed. In order to ensure that these requirements are met, a VPN customer must tell its SP which routes are the matching routes for extranet C-sources and C-RPs. This may be done as part of the provisioning process. Note that this does not necessarily require customer/provider interaction every time the customer adds a new extranet C-source or C-RP, but only when the IP address of the new C-source or C-RP does not match an existing route that is already being distributed as a VPN-IP extranet route. Nevertheless, it seems worthwhile to support an OPTIONAL mechanism that allows a customer to dynamically mark certain routes as being extranet routes. To facilitate this, we define a new Transitive Opaque Extended Community (see [RFC4360], [RFC7153], and Section 9 of this document): the Extranet Source Extended Community. When a Customer Edge (CE) router advertises (via BGP) a route to a PE router and the AFI/SAFI of the route is 1/1, 1/2, 1/4, 2/1, 2/2, or 2/4, the Extranet Source Extended Community MAY be attached to the route. The value field of the Extended Community MUST be set to zero. By placing this Extended Community on a particular route, a CE router indicates to a PE router that the procedures of Sections 4.1, 4.2, and 4.3 are to be applied to that route. That is, the CE router may use this Extended Community to indicate to the PE router that a particular route is to be treated as a route that matches the address of an extranet source and is to be exported accordingly to other VPNs. A PE router that interprets this Extended Community MUST ignore the contents of the value field.
Whether a CE router uses the Extranet Source Extended Community is determined by the configuration of the CE router. If used, the set of routes to which the Extended Community is attached is also determined by configuration of the CE. Note that a particular PE router may or may not support the use of the Extranet Source Extended Community by a particular CE router; this is determined by the service agreement between the SP and its customer. If a CE is advertising SAFI 2 routes to the PE as the UMH-eligible extranet C-source and C-RP routes and the CE is using the Extranet Source Extended Community, it is important that the CE attach that Extended Community to the SAFI 2 routes, rather than just to the corresponding SAFI 1 routes. Otherwise, extranet receivers may not be able to join the (C-S,C-G) or (C-*,C-G) multicast trees. However, if the C-sources and the C-RPs for a given extranet C-group are not all in the same VPN, the Extended Community would also have to be attached to the SAFI 1 routes that match the C-RP addresses and to the SAFI 1 routes that match the addresses of the first-hop designated routers for all the C-sources. Otherwise, the first-hop routers might not be able to send PIM Register messages to the C-RPs, and the C-RPs might not be able to send PIM Register-Stop messages to the first-hop routers. While this Extended Community allows a customer to inform the SP dynamically that certain routes are "extranet routes", it does not allow a customer to control the set of RTs that the route will carry when it is redistributed as a VPN-IP route. Thus, it is only useful when all the extranet routes from a given VRF are exported with exactly the same set of RTs. (cf. Section 4.3.1 of [RFC4364], which does provide a mechanism that, if properly supported by the SP, allows the customer to determine the set of RTs carried by a VPN-IP route.) A CE SHOULD NOT attach the Extranet Source Extended Community to any route for which it uses another method of specifying the RTs to be carried by that route. A CE SHOULD NOT attach the Extranet Source Extended Community to a route unless all the extranet routes from the CE's VPN are intended to carry the same set of RTs. A PE SHOULD ignore the Extranet Source Extended Community if it appears on a route that the CE should not have put it on. A PE that ignores the Extranet Source Extended Community SHOULD NOT follow the procedures of Section 4.4.2. Note that misconfiguration on the CE router can result in the Extranet Source Extended Community being mistakenly attached to a route that is not intended to be exported as an extranet route. This could result in a VPN security violation.
Section 4.4.1) whether it should ignore that Extended Community on route R; if it should ignore the Extended Community, the procedures described in this section are not followed. Otherwise, when the PE originates a VPN-IP route corresponding to route R, the PE MUST attach this Extended Community to that route. A Route Reflector MUST NOT add or remove the Extranet Source Extended Community from the VPN-IP routes reflected by the Route Reflector, including the case where VPN-IP routes received via Internal BGP (IBGP) are reflected to External BGP (EBGP) peers (inter-AS option (c); see Section 10 of [RFC4364]). The value of the Extended Community MUST NOT be changed by the Route Reflector. When re-advertising VPN-IP routes, Autonomous System Border Routers (ASBRs) MUST NOT add/remove the Extranet Source Extended Community from these routes. This includes inter-AS options (b) and (c) (see Section 10 of [RFC4364]). The value of the Extended Community MUST NOT be changed by the ASBRs. When a PE advertises (via BGP) IP routes to a CE, these routes MUST NOT carry the Extranet Source Extended Community unless the PE-CE connection is actually an inter-AS option (a) connection (see Section 10 of [RFC4364]). When the PE-CE connection is not an inter-AS option (a) connection, a CE that receives an IP route with the Extranet Source Extended Community MUST remove it from the route before re-advertising the route. The rules for attaching the Extranet Source Extended Community to a VPN-IP route, and the rules for propagating that Extended Community, are needed in order to support the scenario in which a VPN contains an option (a) interconnect (see Section 10 of [RFC4364]). At the option (a) interconnect, the VPN-IP route gets translated back to an IP route, and the RTs are stripped off before the IP route is propagated. If the Extranet Source Extended Community has also been stripped off, there is no way for the router at the other end of the option (a) interconnect to know that the route represents an extranet source. Thus, the technique of using the Extranet Source Extended Community to dynamically signal that a particular route represents an extranet source will not work correctly across an option (a) interconnect unless the rules in this section are followed.
RFC4360], [RFC7153], and Section 9 of this document). This Extended Community is used only when extranet separation is being used. Its value field MUST be set to zero upon origination, MUST be ignored upon reception, and MUST be passed unchanged by intermediate routers. A Route Reflector MUST NOT add or remove the Extranet Separation Extended Community from the routes it reflects, including the case where routes received via IBGP are reflected to EBGP peers (inter-AS option (c); see Section 10 of [RFC4364]). If a VRF has been provisioned to use extranet separation and that VRF has been provisioned to transmit any extranet C-flows on a P-tunnel that it advertises in an I-PMSI A-D route or a (C-*,C-*) S-PMSI A-D route, then any UMH-eligible routes that are exported from that VRF following the procedures of Sections 4.1, 4.2, and 4.3 MUST carry the Extranet Separation Extended Community. In addition, if an I-PMSI A-D route and/or (C-*,C-*) S-PMSI A-D route exported from that VRF is used to carry extranet traffic, that A-D route MUST also carry the Extranet Separation Extended Community. Further details may be found in Sections 7.3, 7.4.4, and 7.4.5. RFC6514]), VRF A-1 may also need to export a Source Active A-D route specifying that it contains a source of the given C-flow, and VRF B-1 must import that Source Active A-D route. That is, in order for VRF B-1 to receive a
C-flow from a given extranet C-source contained in VRF A-1, VRF A-1 MUST export a set of A-D routes that are "about" that source, and VRF B-1 MUST import them. One way to ensure this is to provision an RT that is carried by all the routes exported from VRF A-1 that are "about" a given extranet C-source and also provision this RT as an import RT at any VRF (such as VRF B-1) that is allowed to receive extranet flows from that source. If the "single PMSI per C-flow" transmission model is being used (with or without extranet separation), there is an additional requirement, stated below, regarding the way RTs are provisioned, as the RTs carried by a UMH-eligible route that matches a given extranet C-source may need to be used to identify the A-D routes that are "about" that source. Consider the following scenario: o IP address S is the address of one system in VPN-A and the address of a different system in VPN-B. o VRF A-1 on PE1 exports UMH-eligible route R1, which is a matching route for S. o VRF A-1 on PE1 exports an A-D route P1 whose PTA identifies a P-tunnel through which VRF A-1 may send traffic whose C-source is S, where one of the following conditions holds: * P1 is an I-PMSI A-D route, OR * P1 is an S-PMSI A-D route whose NLRI contains (C-*,C-*) or (C-*,C-G), OR * P1 is an S-PMSI A-D route whose NLRI contains (C-S,C-G) or (C-S,C-*), BUT the "single C-source per (C-S,C-G) or (C-S,C-*) P-tunnel" policy is not provisioned, OR * P1 is a Source Active A-D route whose NLRI contains (C-S,C-G).
o VRF B-1 on PE1 exports a UMH-eligible route R2, which is a matching route for S. o VRF B-1 on PE1 exports an A-D route P2 whose PTA identifies a P-tunnel on which VRF B-1 may send traffic whose C-source is S, where one of the following conditions holds: * P2 is an I-PMSI A-D route, OR * P2 is an S-PMSI A-D route whose NLRI specifies (C-*,C-*) or (C-*,C-G), OR * P2 is an S-PMSI A-D whose NLRI specifies (C-S,C-G) or (C-S,C-*), BUT the "single C-source per (C-S,C-G) or (C-S,C-*) P-tunnel" policy is not provisioned, OR * P2 is a Source Active A-D route whose NLRI contains (C-S,C-G). As implied by the rules of Section 4.1, there MUST NOT be any RT that is common to both R1 and R2. In addition, the following set of rules for RT assignment MUST be followed when extranets are supported. These rules support all the extranet transmission models described in this specification: o There MUST NOT be any RT that is carried by both P1 and P2. o The intersection of the set of RTs carried by P1 and the set of RTs carried by R1 MUST be non-null, and any VRF that imports both P1 and R1 MUST be configured with an import RT from this intersection. o The intersection of the set of RTs carried by P2 and the set of RTs carried by R2 MUST be non-null, and any VRF that imports both P2 and R2 MUST be configured with an import RT from this intersection.
Suppose that VRF C-1 on PE2 imports P1 and R1 from VRF A-1 while also importing P2 from VRF B-1. Since o R1 is VRF C-1's route to S, o R1 has an RT in common with P1, and o R1 has no RT in common with P2, it can be concluded that VRF C-1 should expect that multicast traffic from S will arrive on the P-tunnel specified in P1. See Sections 6 and 7 for more details on determining the expected P-tunnel for a given extranet C-flow. While the assignment of import and export RTs to routes is a deployment and provisioning issue rather than a protocol issue, it should be understood that failure to follow these rules is likely to result in VPN security violations. Section 2.1.1 of [RFC6513]) is a tunnel that, by default, carries all the multicast traffic of a given MVPN that enters the backbone network via a particular PE. An Inclusive Tunnel is advertised in the PTA of an I-PMSI A-D route.
In the case of IR, this has the following consequence: if an egress PE has n VRFs with receivers for a flow that VRF-S transmits on its I-PMSI, that egress PE will receive n copies of the same packet, one for each of the n VRFs. Note that Section 9.1.1 of [RFC6514] prohibits the "Leaf Information Required" flag from being set in the PTA of an Intra-AS I-PMSI A-D route. If this prohibition is ever removed, the requirement of this section will apply only if VRF-S does not set that flag. RFC6513] and [RFC6514] specify procedures that allow I-PMSIs to be instantiated by IR. The concept of an IR P-tunnel, and the procedures for supporting IR P-tunnels, are explained more fully in [MVPN-IR]. An IR P-tunnel can be thought of as a P2MP tree in which a packet is transmitted from one node on the tree to another by being encapsulated and sent through a unicast tunnel. As discussed in Section 2, when I-PMSIs are used to support extranets, egress PEs MUST have the ability to discard customer multicast data packets that arrive on the wrong P-tunnel. When I-PMSIs are instantiated by IR, this implies that the following two procedures MUST be followed: 1. One of the following three procedures MUST be followed: a. the "Single Forwarder Selection" procedures of Section 9.1.2 of [RFC6513] b. the "native PIM methods" of Section 9.1.3 of [RFC6513] c. the unicast encapsulation used to transmit packets along the IR P-tunnel is such as to enable the receiving node to identify the transmitting node (note that this would not be the case if, for example, the unicast tunnels were MP2P LSPs) and 2. If a PE assigns an MPLS label value in the PTA of an Intra-AS or Inter-AS I-PMSI A-D route that it originates, that label value MUST NOT appear in the PTA of any other I-PMSI or S-PMSI A-D route originated by the same PE.
Failure to follow these procedures would make it impossible to discard packets that arrive on the wrong P-tunnel and thus could lead to duplication of data. If it is desired to support extranets while also using IR to instantiate the PMSIs, an alternative is to use (C-*,C-*) S-PMSIs instead of I-PMSIs. (See [RFC6625], as well as Sections 7.2.2, 7.3.2, and 7.4.4 of this document.) This has much the same effect in the data plane, and there are no restrictions on the type of unicast tunnel that can be used for instantiating S-PMSIs. Section 6.4.5 of [RFC6513] describes a way to support VPNs using I-PMSIs that are instantiated by IR, using no S-PMSIs, but using "explicit tracking" to ensure that a C-flow goes only to egress PEs that have receivers for it. This document does not provide procedures to support extranets using that model. RFC6513], when PIM is used as the PE-PE C-multicast control plane for a particular MVPN, there is a "Multidirectional Inclusive Provider Multicast Service Interface" (MI-PMSI) for that MVPN, and all the PEs of that MVPN must be able to send and receive on that MI-PMSI. Associated with each VRF of the MVPN is a PIM C-instance, and the PIM C-instance treats the MI-PMSI as if it were a LAN interface. That is, the "ordinary" PIM procedures run over the MI-PMSI just as they would over a real LAN interface, except that the data-plane and control-plane "Reverse Path Forwarding (RPF) checks" need to be modified. Section 5.2 of [RFC6513] specifies the RPF check modifications for non-extranet MVPN service. For example, suppose that there are two VPNs: VPN-S and VPN-R. In the absence of extranet support, all the VRFs of VPN-S are connected via one MI-PMSI (call it "the VPN-S MI-PMSI"), and all the VRFs of VPN-R are connected via another ("the VPN-R MI-PMSI"). If we want to provide extranet service in which the extranet C-sources are attached to some set of VPN-S VRFs while the extranet C-receivers are attached to some set of VPN-R VRFs, then we have two choices: 1. either the VPN-R VRFs need to join the VPN-S MI-PMSI, or 2. the VPN-S VRFs need to join the VPN-R MI-PMSI. The first choice is used to support the "single PMSI per C-flow" transmission model. The second choice is used to support the "multiple PMSIs per C-flow" transmission model.
Procedures for both models are described below. To support these models, it must be possible to determine which I-PMSI A-D routes are associated with the VPN-S I-PMSI and which I-PMSI A-D routes are associated with the VPN-R I-PMSI. Procedures are given for assigning RTs to these routes in a way that makes this determination possible. Both models allow the use of S-PMSIs to carry multicast data traffic. If a VRF containing receivers can receive from multiple MI-PMSIs, each S-PMSI must be uniquely associated with a particular MI-PMSI. Procedures are given for assigning RTs to these routes in a way that makes this determination possible. All the procedures specified in Sections 3, 4, and 5 still apply. Note that there are no special extranet procedures for Inter-AS I-PMSI A-D routes or for Leaf A-D routes. Source Active A-D routes are not used when PIM is the PE-PE C-multicast protocol.
The Incoming Extranet RTs and Outgoing Extranet RTs that are configured for a given VRF serve as import RTs for that VRF. They also serve as export RTs, but only for specific routes as specified in Section 6.1.2 below. Note that any VRF that contains both extranet C-sources and extranet C-receivers MUST be configured with both Outgoing Extranet RTs and Incoming Extranet RTs. A VRF MAY be configured with more than one Incoming Extranet RT and/or Outgoing Extranet RT. If it happens to be the case that all C-sources in VPN-S are extranet C-sources allowed to transmit to VPN-R, then VPN-S VRFs MAY be configured such that RT-S is both a non-extranet RT and an Outgoing Extranet RT, and VPN-R VRFs MAY be configured such that RT-S is an Incoming Extranet RT. Section 4 regarding RTs and ambiguous addresses still apply. Section 5.2.2 of [RFC6513]) for a particular IP prefix S. RPF determination is based upon the rules for UMH selection as specified in Section 5.1 of [RFC6513].
This document specifies an additional constraint on the UMH selection procedure. When doing RPF determination for a PIM control message received over a P-tunnel, a route matching prefix S is not considered to be eligible for UMH selection unless there is an RT (call it "RT1"), configured as one of VRF-V's Outgoing Extranet RTs, such that the following two conditions both hold: 1. The route matching S is exported from VRF-V carrying RT1, and 2. An I-PMSI A-D route advertising P-tunnel T (in its PTA) has been imported into VRF-V, and that I-PMSI A-D route carries RT1. RFC6513], each VPN-S VRF must originate an Intra-AS I-PMSI A-D route containing a PTA specifying the P-tunnel to be used as part of the VPN-S MI-PMSI. In the absence of extranet service, this route carries the VRF's non-extranet RT, RT-S. When extranet service is provided (using the "single PMSI per C-flow" model), this route MUST also carry each of the VRF's Outgoing Extranet RTs. Consider a VPN-R VRF that has extranet C-receivers. Per [RFC6513], each VPN-R VRF must originate an Intra-AS I-PMSI A-D route containing a PTA specifying the P-tunnel to be used as part of the VPN-R MI-PMSI. This route carries the VRF's non-extranet RT, RT-R. When extranet service is provided (using the "single PMSI per C-flow" model), the VPN-R VRF MUST also originate one or more additional Intra-AS I-PMSI A-D routes. It MUST originate one additional Intra-AS I-PMSI A-D route for each Incoming Extranet RT with which it has been configured; each such route will carry exactly one of the configured Incoming Extranet RTs. Note that when a VRF originates more than one Intra-AS I-PMSI A-D route, each of them MUST contain a different RD in its NLRI. In addition, we add the requirement that any pair of such routes MUST NOT contain an RT in common.
A VRF with extranet C-sources MUST join the P-tunnels advertised in the imported I-PMSI A-D routes that carry its non-extranet RT or any of its Outgoing Extranet RTs. This set of P-tunnels will be treated as instantiating a single MI-PMSI; the associated PIM C-instance will treat that MI-PMSI as a single LAN and will run PIM procedures on that LAN, as specified in [RFC6513]. The fact that the MI-PMSI attaches to VRFs of different VPNs is not known to the PIM C-instance of the VRF containing the sources. A VRF with extranet C-receivers MUST join the P-tunnels advertised in all the imported I-PMSI A-D routes. The set of P-tunnels advertised in the I-PMSI A-D routes that carry a particular Incoming Extranet RT are treated as instantiating a particular MI-PMSI. So, a VRF with C-receivers will "see" several MI-PMSIs, one corresponding to the non-extranet, and as many as one for each configured Incoming Extranet RT. The PIM C-instance associated with the VRF will treat each of these MI-PMSIs as a separate LAN interface. As an example, suppose that: o All VPN-R VRFs are configured with RT-R as a non-extranet import and export RT, and o VPN-R VRFs with extranet receivers are configured with RT-S-to-R as an Incoming Extranet RT, and o VPN-S VRFs with extranet transmitters are configured with: * RT-S as a non-extranet import and export RT * a list of IP addresses that are the addresses of the extranet sources * RT-S-to-R as an Outgoing Extranet RT VPN-S VRFs will then export UMH-eligible routes matching extranet C-sources, and these routes will carry both RT-S and RT-S-to-R. Each VPN-S VRF will also export an Intra-AS I-PMSI A-D route that carries both RT-S and RT-S-to-R. VPN-R VRFs will originate and export two Intra-AS I-PMSI A-D routes: one carrying RT-R and one carrying RT-S-to-R. The Intra-AS I-PMSI A-D route with RT-S-to-R will be imported into the VPN-S VRFs. VPN-R will regard all the I-PMSI A-D routes it has exported or imported with RT-S-to-R as part of a single MI-PMSI. VPN-R will regard all the I-PMSI A-D routes it has exported or imported with RT-R as part of a second MI-PMSI. The PIM C-instance associated with
a VPN-R VRF will treat the two MI-PMSIs as two separate LAN interfaces. However, the VPN-S VRFs will regard all the I-PMSI A-D routes imported with RT-S or RT-S-to-R as establishing only a single MI-PMSI. One can think of this as follows: the VPN-R VRFs have joined the VPN-S MI-PMSI as well as the VPN-R MI-PMSI. Extranets consisting of more than two VPNs are easily supported as follows. Suppose that there are three VPNs: VPN-A, VPN-B, and VPN-C. VPN-A and VPN-B have extranet C-sources, and VPN-C contains receivers for both VPN-A extranet C-sources and VPN-B extranet C-sources. In this case, the VPN-C VRFs that have receivers for both VPN-A and VPN-B sources may be provisioned as follows. These VPN-C VRFs may be provisioned with RT-C as a non-extranet RT, and with RT-A-to-C and RT-B-to-C as Incoming Extranet RTs. In this case, the VPN-C VRFs that are so provisioned will originate three Intra-AS I-PMSI A-D routes (each with a different RD in its NLRI), each of which carries exactly one of the three RTs just mentioned. The VPN-B VRFs with extranet C-sources will be provisioned with RT-B-to-C as an Outgoing Extranet RT, and the VPN-A VRFs will be provisioned with RT-A-to-C as an Outgoing Extranet RT. The result will be that the PIM C-instance associated with a VPN-C VRF will see three LAN interfaces: one for the non-extranet and one for each of the two extranets. This generalizes easily to the case where there are VPN-C receivers in n different extranets (i.e., receiving extranet flows whose sources are in n different VPNs). Suppose again that there are three VPNs -- VPN-A, VPN-B, and VPN-C -- but in this example VPN-A is the only one with extranet sources while VPN-B and VPN-C both have receivers for the VPN-A extranet sources. This can be provisioned as either one extranet or two extranets. To provision it as one extranet, the VPN-A VRFs are configured with one Outgoing Extranet RT (call it "RT-A-extranet"). The VPN-B and VPN-C VRFs with extranet receivers will be provisioned with RT-A-extranet as the Incoming Extranet RT. Thus, the VPN-B and VPN-C VRFs will each originate two Intra-AS I-PMSI A-D routes: one for the non-extranet and one for the extranet. From a given VRF, the Intra-AS I-PMSI A-D route for the extranet will carry RT-A-extranet but will not share any RT with the non-extranet A-D routes exported from the same VRF. The result is that the VPN-B and VPN-C VRFs each belong to two MI-PMSIs: one for the extranet and one for the intranet. The MI-PMSI for the extranet attaches VPN-A VRFs, VPN-B VRFs, and VPN-C VRFs.
Alternatively, one could provision the VPN-A VRFs so that some UMH-eligible extranet source routes carry an RT that we will call "RT-A-to-B" and some carry an RT that we will call "RT-A-to-C". The VPN-A VRFs would be configured with both of these as Outgoing Extranet RTs. To allow an extranet flow from a VPN-A source to have both VPN-B and VPN-C receivers, the UMH-eligible route for that source would carry both RTs. VPN-B VRFs (but not VPN-C VRFs) would be provisioned with RT-A-to-B as an Incoming Extranet RT. VPN-C VRFs (but not VPN-B VRFs) would be provisioned with RT-A-to-C as an Incoming Extranet RT. Following the rules above, if any VPN-A extranet source is to have both VPN-B and VPN-C receivers, the VPN-B and VPN-C VRFs will each originate two I-PMSI A-D routes: one for the extranet and one for the non-extranet. The single Intra-AS I-PMSI A-D route originated by the VPN-A VRFs will have both RT-A-to-B and RT-A-to-C among its RTs (as well as VPN-A's non-extranet RT). The extranet I-PMSI A-D route originated from a VPN-B VRF would have RT-A-to-B, and the extranet I-PMSI A-D route originated from a VPN-C VRF would have RT-A-to-C. If a given VRF contains both extranet C-receivers and extranet C-sources, the procedures described above still work, as the VRF will be configured with both Incoming Extranet RTs and Outgoing Extranet RTs; the VRF functions as both a VPN-S VRF and a VPN-R VRF. Section 7 of [RFC6513]) sent on the MI-PMSI, the S-PMSI is considered to be part of the same LAN interface as the corresponding MI-PMSI. When the bindings of C-flows to particular S-PMSIs are announced via S-PMSI A-D routes, any S-PMSI A-D route exported from that VRF MUST have an RT in common with exactly one of the Intra-AS A-D routes exported from that VRF, and this MUST be one of the VRF's Outgoing Extranet RTs. Further, the S-PMSI A-D route MUST NOT have an RT in common with any other Intra-AS A-D route exported from a VRF on the same PE. A given S-PMSI A-D route will be considered to "correspond" to the MI-PMSI of the Intra-AS I-PMSI A-D route (originated from the same PE) with which it shares an RT.
The MI-PMSI that corresponds to a given S-PMSI is determined as follows: o If (1) there is an Intra-AS I-PMSI A-D route originated by the same PE that originated the S-PMSI A-D route, (2) those two routes have an RT in common, and (3) that RT is one of the VRF's Incoming Extranet RTs, then the S-PMSI corresponds to the I-PMSI associated with that Intra-AS I-PMSI A-D route. o Otherwise, if (1) there is an Inter-AS I-PMSI A-D route originated in the same AS as the S-PMSI A-D route, (2) those two routes have an RT in common, and (3) that RT is one of the VRF's Incoming Extranet RTs, then the S-PMSI corresponds to the I-PMSI associated with that Inter-AS I-PMSI A-D route. o Otherwise, there must be a configuration error (a violation of the requirements of Sections 3, 4, and 5 of this document). When wildcard S-PMSIs are used, the rules given in [RFC6625] for determining whether a given S-PMSI A-D route is a "match for reception" to a given (C-S,C-G) or (C-*,C-G) are modified as follows: A given S-PMSI A-D route MUST NOT be considered to be a "match for reception" for a given (C-S,C-G) or (C-*,C-G) state UNLESS that S-PMSI A-D route "corresponds" (as defined above) to the MI-PMSI that is the incoming interface for the given state. The rules given in [RFC6625] for determining whether a given S-PMSI A-D route is a "match for transmission" are unchanged. Section 5.1 of [RFC6513]. PE1 determines the set of RTs carried by that route. PE1 then checks to see if there is an Intra-AS I-PMSI A-D route, currently originated by PE1, that has an RT in common with the selected UMH route for S.
If the rules of Sections 3, 4, and 5 have been followed, each of PE1's selected UMH routes will share an RT with a single one of PE1's currently originated Intra-AS I-PMSI A-D routes. If this is so, the Join is sent on the P-tunnel advertised in the PTA of that route. Otherwise, the Join MUST NOT be sent. In essence, this procedure makes the RPF check for C-S resolve to the MI-PMSI that is serving as the next-hop "interface" to C-S. If a PE receives a PIM Join(*,G) from a CE, the procedure for doing the RPF check is the same, except that the selected UMH route will be a route to the C-RP associated with the C-G group. RFC6513] and [RFC6625], with one new restriction: a VPN-S VRF always transmits a multicast data packet either on the VPN-S MI-PMSI or on an S-PMSI that corresponds to the VPN-S MI-PMSI. From the perspective of the PIM C-instance, there is only one outgoing interface. When a PIM C-instance receives a multicast data packet from a given P-tunnel and that P-tunnel is being used to instantiate an MI-PMSI, the MI-PMSI of which the P-tunnel is a part (see Sections 6.2.1 and 6.2.2) is considered to be the packet's incoming interface. If the packet is received on a P-tunnel that was advertised in an S-PMSI A-D route, the packet's incoming interface is the MI-PMSI to which that S-PMSI route corresponds, as defined in Section 6.2.2. Ordinary PIM rules for data-plane RPF checks apply. Following ordinary PIM procedures, packets arriving from an unexpected incoming interface are discarded. This eliminates any problems due to the ambiguities described in Sections 2.1 and 2.2.
In the "single PMSI per C-flow" transmission model (as described in Section 6.2), a PE that needs to transmit a multicast data packet to a set of other PEs transmits the packet on a single PMSI. This means that if a packet needs to be transmitted from a VPN-A VRF and received at a VPN-B VRF and a VPN-C VRF, there must be some P-tunnel from which the VPN-B and VPN-C VRFs can both receive packets. In the "multiple PMSIs per C-flow" transmission model, a PE that needs to transmit a multicast data packet to a set of other PEs may transmit the packet on several different PMSIs. (Of course, any given packet is transmitted only once on a given P-tunnel.) For example, if a C-flow (C-S,C-G) has a VPN-A C-source, a VPN-B receiver, and a VPN-C receiver, there could be one PMSI that the VPN-A VRF uses to transmit the packet to the VPN-B VRFs and another PMSI that the VPN-A VRF uses to transmit the packet to the VPN-C VRFs. RFC6513], each VPN-R VRF must originate an Intra-AS I-PMSI A-D route containing a PTA specifying the P-tunnel to be used as part of the VPN-R MI-PMSI. In the absence of extranet service, this route carries the VRF's non-extranet RT, RT-R. When extranet service is provided (using the "single PMSI per C-flow" model), this route MUST also carry each of the VRF's Incoming Extranet RTs. Consider a VPN-S VRF that has extranet C-sources. Per [RFC6513], each VPN-S VRF must originate an Intra-AS I-PMSI A-D route containing a PTA specifying the P-tunnel to be used as part of the VPN-S MI-PMSI. This route carries the VRF's non-extranet RT, RT-S. When extranet service is provided using the "multiple PMSIs per C-flow" model, the VPN-S VRF MUST also originate one or more additional Intra-AS I-PMSI A-D routes. It MUST originate one additional Intra-AS I-PMSI A-D route for each Outgoing Extranet RT with which it has been configured; each such route will have a distinct RD and will carry exactly one of the configured Outgoing Extranet RTs. As with the "single PMSI per C-flow" transmission model, VRFs containing extranet C-receivers need to import UMH-eligible extranet C-source routes from VRFs containing C-sources. This is ensured by the rules of Sections 3, 4, and 5. However, in the "multiple PMSIs per C-flow" model, a VRF containing only C-receivers originates only a single Intra-AS I-PMSI A-D route carrying the non-extranet RT and all the Incoming Extranet RTs.
When a VRF containing C-receivers imports Intra-AS I-PMSI A-D routes that carry the non-extranet RT or one of the Incoming Extranet RTs, the P-tunnels specified in the PTA of all such routes are considered to be part of the same MI-PMSI. That is, the associated PIM C-instance will treat them as part of a single interface. In this model, it is the VRF containing extranet C-sources that MUST originate multiple Intra-AS I-PMSI A-D routes. Each such route MUST have a distinct RD, and the set of RTs carried by any one of these routes MUST be disjoint from the set carried by any other. There MUST be one such route for each of the VRF's Outgoing Extranet RTs, and each such route MUST carry exactly one of the VRF's Outgoing Extranet RTs. The VRFs containing extranet C-sources MUST also import all the A-D routes originated by the VRFs containing extranet C-receivers. If a set of originated and/or imported Intra-AS I-PMSI A-D routes have an RT in common and that RT is one of the VRF's Outgoing Export RTs, then those routes are considered to be "about" the same MI-PMSI. The PIM C-instance of the VRF treats each MI-PMSI as a LAN interface. In effect, if VPN-S has only extranet C-sources and VPN-R has only extranet C-receivers, this model has the VPN-S VRFs join the VPN-R MI-PMSI. The VPN-S VRFs will thus be attached to multiple MI-PMSIs, while the VPN-R VRFs are attached to only one. The fact that the VPN-R MI-PMSI is attached to VPN-S VRFs is not known to the PIM C-instance at the VPN-R VRFs. If a VPN-A VRF has extranet C-sources allowed to send to C-receivers in a VPN-B VRF and the VPN-B VRF has C-sources allowed to send to C-receivers in the VPN-A VRF, the above procedures still work as specified. Following normal PIM procedures, when the PIM C-instance at a VRF with extranet C-sources receives a Join(C-S,C-G) or a Join(C-*,C-G) over an MI-PMSI, it may create (C-S,C-G) or (C-*,C-G) state, and the MI-PMSI over which the Join was received may be added to the set of outgoing interfaces for that multicast state. If n MI-PMSIs are added to the outgoing interface list for a particular multicast state, a multicast data packet may need to be replicated n times and transmitted once on each of the n MI-PMSIs. Since all of the multicast data packets received from another PE are received over a single emulated LAN, it is not necessary to have any special procedures to determine a packet's incoming interface. The ambiguities described in Sections 2.1 and 2.2 do not occur, because a VPN-R VRF can only receive multicast data traffic that has been requested by a VPN-R VRF.