31.4.2 IPv6 PIM-SM

(1) Rendezvous Point and Bootstrap Router (BSR)

Rendezvous points and bootstrap routers (BSRs) can be set up through configuration. The Switch can use a maximum of 16 BSRs in each network (VPN). Note, however, that separate rendezvous points and bootstrap routers can be used for IPv4 PIM-SM and IPv6 PIM-SM.

The BSR reports the IPv6 address and other rendezvous point information to all multicast interfaces. The information is sent to the link-local multicast address (ff02::d) and reported to all PIM routers on a hop-by-hop basis. For the Rendezvous Point router and the router other than BSR, set PIM for the Rendezvous Point router and BSR interface. The following figure shows the roles of the rendezvous point and the BSR.

The BSR (PIM-SM router C) reports rendezvous point information to all IPv6 multicast interfaces. Routers receiving rendezvous point information learn the IPv6 address of the rendezvous point, and report rendezvous point information to all other interfaces for which IPv6 PIM routers exist.

(2) Notification of group participation information to the rendezvous point

Each router reports the group-joining information learned by using MLD to the rendezvous point. Note that the sender and destination IPv6 addresses used for this notification are the device addresses of the corresponding routers. The rendezvous point understands the existence of groups for each interface by receiving IPv6 group information. The following figure shows how group-joining information is reported to the rendezvous point.

In this diagram, each host joins group 1 by using MLD. PIM-SM router D and PIM-SM router E learn information about group 1, and report this information to the rendezvous point (PIM-SM router C). The rendezvous point (PIM-SM router C) receives this information, and learns that group 1 exists on the interface from which reception occurred.

(3) IPv6 multicast packet communication (encapsulation)

When the sender sends an IPv6 multicast packet bound for group 1, PIM-SM router A IPv6-encapsulates (creates a Register packet) and sends the packet to the rendezvous point (PIM-SM router C). For the Switch, the source and destination IPv6 addresses used for this notification are the device addresses of the corresponding routers. (IPv6 addresses of the rendezvous points have been learned in (1) Rendezvous point and bootstrap router (BSR).)

When the rendezvous point (PIM-SM router C) receives a IPv6 encapsulated packet, it decapsulates the packet and forwards the multicast packet addressed to group 1 to the interface on which group 1 exists. (The existence of group 1 has been learned in (2) Notification of group join information to the rendezvous point.) When PIM-SM router D and PIM-SM router E receive IPv6 multicast packets destined for group 1, it forwards IPv6 multicast packets to the interfaces on which group 1 exists (the presence of group 1 is learned in MLD "(2) Advertising group joins to rendezvous points"). The following figure shows multicast packet communication (encapsulation) via a rendezvous point.

(4) IPv6 Multicast Packet Communication (Decapsulation)

When the rendezvous point (PIM-SM router C) receives a IPv6 encapsulated packet, it decapsulates the packet and forwards IPv6 multicast packet addressed to group 1 to the interface on which group 1 exists (described in (3) IPv6 multicast packet communication (encapsulation)).

After this processing has been completed, the rendezvous point reports, over the shortest path, information about group 1 to the sending server determined based on the existing IPv6 unicast routing information. The destination address used for this notification is the link-local multicast address for all PIM routers (ff02::d).

When PIM-SM router B and PIM-SM router A receive information about group 1, they learn that group 1 exists on the interface from which the information was received. Upon receiving an IPv6 multicast packet bound for group 1 from the sending server, PIM-SM router A forwards the packet to the relevant interface without IPv6-encapsulating the packet. When PIM-SM routers B, C, D, and E receive the IPv6 multicast packet, they forward it to the interface on which group 1 exists. The following figure shows IPv6 multicast packet communication (decapsulation).

(5) Shortest-path multicast packet communication

When PIM-SM router D and PIM-SM router E receive IPv6 multicast packets destined for group 1 of the source server (described in (4) IPv6 multicast packet communication (decapsulation)), it advertises group 1 information to the source server in the shortest path (pre-existing IPv6 unicast routing information). The destination address used for this notification is the link-local multicast address for all PIM routers (ff02::d).

When PIM-SM router A receives information about group 1 from PIM-SM routers D and E, it learns that group 1 exists on the interface from which the information was received. When PIM-SM router A receives a multicast packet bound for group 1 from the sending server, it forwards the packet to the relevant interface. The following figure shows multicast packet communication over the shortest path.

(6) IPv6 Multicast Delivery Tree pruning

When a host leaves group 1 over MLD, PIM-SM router D reports pruning information for group 1 to the interfaces to which information about group 1 was being reported. The destination address used for this notification is the link-local multicast address for all PIM routers (ff02::d).

When PIM-SM router A receives the pruning information for group 1, it stops forwarding IPv6 multicast packets bound for group 1 to the interface from which the information was received. The following figure shows IPv6 multicast delivery tree pruning.

(7) Election of Rendezvous Point

If more than one rendezvous point candidate exists, the rendezvous point is selected according to the selection algorithms described in RFC2362 and RFC4601. The rendezvous point selection algorithm is specified in the configuration command ipv6 pim rp-mapping-algorithm. Note that the rendezvous point election algorithm must be the same in the network.

The following tables show the selection conditions for RFC2362 and RFC4601 rendezvous points and the priorities of the selection conditions.