Extreme Networks ExtremeWare XOS Command Reference Manual page 1526

IP Multicast Commands
PIM Sparse Mode (PIM-SM)
Unlike PIM-DM, PIM-SM is an explicit join and prune protocol, and it supports shared trees as well as
shortest path trees (SPTs). The routers must explicitly join the group(s) in which they are interested in
becoming a member, which is beneficial for large networks that have group members who are sparsely
distributed.
Using PIM-SM, the router sends a join message to the rendezvous point (RP). The RP is a central
multicast router that is responsible for receiving and distributing multicast packets. By default, the RP is
selected dynamically (but not automatically). You can also define a static RP in your network, using the
following command:
configure pim crp static <ip_address>
When a router has a multicast packet to distribute, it encapsulates the packet in a unicast message and
sends it to the RP. The RP decapsulates the multicast packet and distributes it among all member
routers.
When a router determines that the multicast rate from a particular group has exceeded a configured
threshold, that router can send an explicit join to the originating router. When this occurs, the receiving
router gets the multicast directly from the sending router, and bypasses the RP.
NOTE
You can run either PIM-DM or PIM-SM per VLAN.
PIM Mode Interoperation
An Extreme Networks switch can function as a PIM multicast border router (PMBR). A PMBR
integrates PIM-SM and PIM-DM traffic.
When forwarding PIM-DM traffic into a PIM-SM network, the PMBR notifies the RP that the PIM-DM
network exists. The PMBR forwards PIM-DM multicast packets to the RP, which in turn forwards the
packets to those routers that have joined the multicast group in the PIM-SM domain.
The PMBR also forwards PIM-SM traffic to a PIM-DM network. The PMBR sends a join message to the
RP and the PMBR floods traffic from the RP into the PIM-DM network.
No commands are needed to enable PMBR mode interoperation. PMBR mode translation is
automatically enabled when a dense mode interface and a sparse mode interface are enabled on the
same switch.
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ExtremeWare XOS 11.3 Command Reference