• PIM Allow RP only supports connecting PIM SM domains.

• PIM Allow RP is applicable for downstream traffic only, that is, it is only applicable for building the shared tree.

• PIM Allow RP does not work with Auto-RP or Boot Strap Router (BSR). Only static configuration is supported. However, it does allow the RP used in the consumer network to be different than the one configured statically in the service provider network.

• PIM Allow RP is restricted to use only the route-map.

• PIM Allow RP does not support the IPv6 Multicast prior to Cisco NX-OS Release 8.4(2). IPv6 PIM Allow RP is supported from Cisco NX-OS Release 8.4(2).

• PIM Allow RP does not support the RPM with “Source”. PIM Allow RP Information AboutPIM AllowRP.

• When the Allow-RP configuration is added with a non-existent RPM, all Joins/Prunes get rejected.

• When the Allow-RP configuration is added with an RPM having PERMIT-ALL or DENY-ALL, all Joins/Prunes are either accepted or discarded accordingly.

Rendezvous Points

A rendezvous point (RP) is a role that a device performs when operating in Protocol Independent Multicast (PIM) Sparse Mode (SM). An RP is required only in networks running PIM SM. In the PIM-SM model, only network segments with active receivers that have explicitly requested multicast data will be forwarded the traffic. This method of delivering multicast data is in contrast to PIM Dense Mode (PIM DM). In PIM DM, multicast traffic is initially flooded to all segments of the network. Routers that have no downstream neighbors or directly connected receivers prune back the unwanted traffic. An RP acts as the meeting place for sources and receivers of multicast data. In a PIM-SM network, sources must send their traffic to the RP. This traffic is then forwarded to receivers down a shared distribution tree.

By default, when the first hop device of the receiver learns about the source, it will send a Join message directly to the source, creating a source-based distribution tree from the source to the receiver. This source tree does not include the RP unless the RP is located within the shortest path between the source and receiver. In most cases, the placement of the RP in the network is not a complex decision.

By default, the RP is needed only to start new sessions with sources and receivers. Consequently, the RP experiences little overhead from traffic flow or processing. In PIM version 2, the RP performs less processing than in PIM version 1 because sources must only periodically register with the RP to create state.

PIM Allow RP

There are three types of networks: publisher, consumer, and transport. Many publisher networks can originate content and many consumer networks can be interested in the content. The transport network, owned and operated by a service provider, connects the publisher and the consumer networks.

The consumer and the transport networks are connected as follows: For a specific group range, or all-groups range (similar to a default route), the service provider defines a particular rendezvous point (RP), such as RP-A. Reverse path forwarding of RP-A from a consumer device will cause a (*,G) Join to be sent towards the transport network. For the same group, the service provider may define a different RP, such as RP-B, that is used to build the shared tree within the transport network for G. RP-A and RP-B are typically different RPs and each RP is defined for different group ranges. RFC 4601 dictates that if a device receives a (*, G) Join and the RP that is specified in the (*, G) Join is different than what the receiving device expects (unknown RPs), the incoming (*, G) Join must be ignored.

The PIM Allow RP feature is introduced in Cisco NX-OS Release 8.4(1). This feature enables the receiving device to use its own RP to create state and build shared trees when an incoming (*, G) Join is processed and a different RP is identified. This allows the receiving device to accept the (*, G) Join from the different RP. A route-map is used to control which RP address and/or group addresses the (*,G) join is for. The RP address and the group address in the (*,G) join message is matched against any RP and group addresses specified in the route-map. Support for IPv6 is introduced in Cisco NX-OS Release 8.4(2).

PIM Allow RP is only applicable for downstream traffic, for building the shared tree. It does not work with Auto-RP or BSR. Only static configuration is supported. However, PIM Allow RP does compensate for the embedded RP in the consumer network to be different than the one configured statically in the transport network.