Pim Sparse Mode - Extreme Networks ExtremeWare XOS Guide Manual

IP Multicast Routing
Licensing
To use the complete PIM functionality, you must have a Core license installed on your switch. The
MSM-1 ships with a Core license. The Aspen 8810 switch ships with an Advanced Edge license; you can
obtain a Core License for the switch from Extreme Networks.
A subset of PIM, called PIM Edge Mode, is available with an Advanced Edge license.
PIM Edge Mode
PIM Edge Mode is a subset of PIM available on platforms with an Advanced Edge license. There are
only three restrictions on PIM Edge Mode:
The switch will not act as a candidate RP.
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The switch will not act as a candidate BSR.
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At most, two Active PIM-SM interfaces are permitted. There is no restriction on the number of
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Passive interfaces (within the limit of the maximum IP interfaces).
Only PIM Sparse Mode (PIM-SM) is supported in this mode.
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Active PIM interfaces can have other PIM enabled routers on them. Passive interfaces should only have
host sourcing or receiving multicast traffic.
PIM Dense Mode
Protocol-Independent Multicast - Dense Mode (PIM-DM) is a multicast routing protocol. PIM-DM is a
broadcast and prune protocol, which allows you to prune and graft multicast routes.
PIM-DM routers perform reverse path multicasting (RPM). However, instead of exchanging its own
unicast route tables for the RPM algorithm, PIM-DM uses the existing unicast routing table for the
reverse path. As a result, PIM-DM requires less system memory.

PIM Sparse Mode

Unlike PIM-DM, Protocol-Independent Multicast - Sparse Mode (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 that 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 the initial multicast packets. You can
configure a dynamic or static RP.
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 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.
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