HP VPN Firewall Appliances Appendix Protocol Reference

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Figure 69 DR election
As shown in Figure 69, the DR election process is as follows:
1. Routers on the shared-media network send hello messages to one another. The hello messages
contain the router priority for DR election. The router with the highest DR priority will become the
DR.
2. In the case of a tie in the router priority, or if any router in the network does not support carrying
the DR-election priority in hello messages, the router with the highest IPv6 link-local address will
win the DR election.
When the DR works abnormally, a timeout in receiving a hello message triggers a new DR election
process among the other routers.
RP discovery
The RP is the core of an IPv6 PIM-SM domain. For a small-sized, simple network, one RP is enough for
forwarding IPv6 multicast information throughout the network, and the position of the RP can be statically
specified on each router in the IPv6 PIM-SM domain. An RP can serve multiple IPv6 multicast groups, but
a given IPv6 multicast group can have only one RP to serve it at a time.
In most cases, however, an IPv6 PIM-SM network covers a wide area and a huge amount of IPv6
multicast traffic must be forwarded through the RP. To lessen the RP burden and optimize the topological
structure of the RPT, you can configure multiple C-RPs in an IPv6 PIM-SM domain. Among them, an RP is
dynamically elected through the bootstrap mechanism. Each elected RP serves a different multicast group
range. For this purpose, you must configure a BSR.
A BSR serves as the administrative core of the IPv6 PIM-SM domain. An IPv6 PIM-SM domain can have
only one BSR, but can have multiple C-BSRs. If the BSR fails, a new BSR is automatically elected from the
C-BSRs to avoid service interruption. A device can serve as a C-RP and a C-BSR at the same time.
As shown in Figure 70, ea
ch C-RP periodic
ally unicasts its advertisement messages (C-RP-Adv messages)
to the BSR. A C-RP-Adv message contains the address of the advertising C-RP and the IPv6 multicast
group range it serves.
The BSR collects these advertisement messages and chooses the appropriate C-RP information for each
multicast group to form an RP-set, which is a database of mappings between IPv6 multicast groups and