How Ipv6 Pim-Sm Works - 3Com MSR 50 Series Configuration Manual

How IPv6 PIM-SM Works

IPv6 PIM-SM assumes that no hosts need to receive IPv6 multicast data. In the
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IPv6 PIM-SM mode, routers must specifically request a particular IPv6 multicast
stream before the data is forwarded to them. The core task for IPv6 PIM-SM to
implement IPv6 multicast forwarding is to build and maintain rendezvous point
trees (RPTs). An RPT is rooted at a router in the IPv6 PIM domain as the
common node, or rendezvous point (RP), through which the IPv6 multicast
data travels along the RPT and reaches the receivers.
When a receiver is interested in the IPv6 multicast data addressed to a specific
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IPv6 multicast group, the router connected to this receiver sends a join message
to the RP corresponding to that IPv6 multicast group. The path along which the
message goes hop by hop to the RP forms a branch of the RPT.
When a multicast source sends an IPv6 multicast packet to an IPv6 multicast
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group, the router directly connected with the multicast source first registers the
multicast source with the RP by sending a register message to the RP by
unicast. The arrival of this message at the RP triggers the establishment of an
SPT. Then, the multicast source sends subsequent IPv6 multicast packets along
the SPT to the RP. Upon reaching the RP, the IPv6 multicast packet is duplicated
and delivered to the receivers along the RPT.
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IPv6 multicast traffic is duplicated only where the distribution tree branches, and
this process automatically repeats until the IPv6 multicast traffic reaches the
receivers.
The working mechanism of IPv6 PIM-SM is summarized as follows:
Neighbor discovery
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DR election
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RP discovery
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Embedded RP
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RPT establishment
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IPv6 Multicast source registration
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Switchover from RPT to SPT
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Assert
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Neighbor discovery
IPv6 PIM-SM uses exactly the same neighbor discovery mechanism as IPv6 PIM-DM
does. Refer to "Neighbor discovery" on page
DR election
IPv6 PIM-SM also uses hello messages to elect a designated router (DR) for a
multi-access network. The elected DR will be the only multicast forwarder on this
multi-access network.
In the case of a multi-access network, a DR must be elected, no matter this
network connects to IPv6 multicast sources or to receivers. The DR at the receiver
side sends join messages to the RP; the DR at the IPv6 multicast source side sends
register messages to the RP.
IPv6 PIM Overview
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