PIMv6 is a family of multicast routing protocols for IPv6 networks that provide one-to-many and many-to-many distribution of data over a LAN or WAN, or over the internet. PIMv6 is termed protocol-independent because PIMv6 does not include its own topology discovery mechanism. Instead, PIMv6 uses routing information supplied by other traditional routing protocols, such as the BGP.
There are two supported modes in the PIMv6 Protocol:
Sparse mode
PIM-SM uses a pull model to deliver multicast traffic. Only network segments with active receivers, which explicitly request the data, receive the traffic. PIM-SM distributes information about active sources by forwarding data packets on the shared tree.
PIM-SM initially uses shared trees, so it requires the use of an RP, which must be configured in the network. Sources register with the rendezvous point and subsequently forward data down the shared tree to the receivers. The edge routers learn about a particular source when they receive data packets on the shared tree from that source through the RP. The edge router then sends PIMv6 (source or group) join messages to that source.
Each router along the reverse path compares the unicast routing metric of the RP address to the metric of the source address. If the metric for the source address is better, the router forwards a PIMv6 (source or group) join message to the source. If the metric for the RP is equal or better, the join message is sent in the same direction as the RP. In this case, the shared tree and the source tree are the same.
Source-specific multicast
SSM bypasses the shared tree of PIM-SM and immediately creates the shortest-path tree. SSM accomplishes this because:
MLDv2 can specify the source in its request to the local router.
Sources must be able to inform receivers of their existence through a method other than registering with the network (for example, a web page).