31.4.3 Neighbor Detection

Each IPv6 PIM router regularly distributes an IPv6 PIM-Hello message to all interfaces for which IPv6 PIM is enabled. Distribution of the information is performed by sending the message to the link-local multicast address for all PIM routers (ff02::d). Each IPv6 PIM router dynamically detects neighboring IPv6 PIM routers by receiving IPv6 PIM-Hello messages from them. The Switch supports the Generation ID option for PIM-Hello messages (in accordance with RFC 4601 and draft-ietf-pim-sm-bsr-07).

A Generation ID is a 32-bit random number for each multicast interface that is appended when PIM-Hello messages are sent. Generation IDs are regenerated when the status of the multicast interface changes to Up. When the Generation ID option is added to a received PIM-Hello message, the Generation ID is recorded to enable neighboring switches to detect interface failure when the Generation ID changes. When a Generation ID change is detected, updates to neighbor switch information, PIM-Hello messages, PIM Bootstrap messages, and PIM Join/Prune messages are sent without waiting for regular advertisement. This process allows multicast routing information to be relearned quickly.

In addition to the link-local address set for the sender interface, PIM-Hello messages sent by the Switch includes an address list, as optional data (type 24 and 65001) of PIM-Hello messages. By receiving the optional data, the Switch can recognize addresses other than the link-local addresses of neighboring IPv6 PIM routers.

If the next hop of the Switch for a message due to arrive at the IPv6 multicast sender does not have a link-local address, the Switch can detect the IPv6 PIM routers to the sender by using the address list.

The following figure shows how neighboring PIM router addresses are received.

Figure 31-13: PIM-Hello messaging to receive neighboring router addresses