Netgear XCM8806 - 8800 SERIES 6-SLOT CHASSIS SWITCH ユーザーズマニュアル
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Chapter 27. Multicast Routing and Switching
NETGEAR 8800 User Manual
Note:
This feature is supported at and above the license level listed for this
feature in the license tables in
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.
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-DM with State Refresh
The PIM-DM State Refresh feature keeps the PIM-DM prune state from timing out by
periodically sending a state refresh control message down the source tree. These control
messages reset the prune hold time timer on each pruned interface and prevent the
bandwidth waste that occurs with each prune, time-out, and flood cycle.
periodically sending a state refresh control message down the source tree. These control
messages reset the prune hold time timer on each pruned interface and prevent the
bandwidth waste that occurs with each prune, time-out, and flood cycle.
When a topology change occurs, the PIM-DM State Refresh feature improves network
convergence. For example, suppose that an S, G entry on S5 in
convergence. For example, suppose that an S, G entry on S5 in
is removed due to
non-availability of a route. Without PIM-DM State Refresh, multicast traffic is blocked for
minutes (due to a time-out on the upstream routers). In the meantime if an IGMP member or
a PIM-DM neighbor joins S5, there is no way to pull traffic down immediately because S5
does not have any S, G information. State refresh control messages solve this problem by
indicating S, G state information periodically to all downstream routers. When S5 receives a
state refresh from S3, it scans the S, G information and all pending requests from PIM-DM
neighbors and IGMP members. If there are pending requests for the group in the state
refresh message, S5 can immediately send a graft message upstream to circumvent the
upstream timers and pull multicast traffic to its members and neighbors.
minutes (due to a time-out on the upstream routers). In the meantime if an IGMP member or
a PIM-DM neighbor joins S5, there is no way to pull traffic down immediately because S5
does not have any S, G information. State refresh control messages solve this problem by
indicating S, G state information periodically to all downstream routers. When S5 receives a
state refresh from S3, it scans the S, G information and all pending requests from PIM-DM
neighbors and IGMP members. If there are pending requests for the group in the state
refresh message, S5 can immediately send a graft message upstream to circumvent the
upstream timers and pull multicast traffic to its members and neighbors.
To enable, configure, and disable the PIM-DM State Refresh feature, use the following
commands:
commands:
configure pim state-refresh {vlan} [<vlanname> | all] [on | off]
configure pim state-refresh timer origination-interval <interval>
configure pim state-refresh timer source-active-timer <interval>
configure pim state-refresh ttl <ttlvalue>
PIM Sparse Mode
Unlike PIM-DM, Protocol-Independent Multicast - Sparse Mode (PIM-SM) is an explicit join
and prune protocol, which means that multicast receivers, and the routers that support them,
must join multicast groups before they receive multicast traffic. When all receivers on a
network branch leave a multicast group, that branch is pruned so that the multicast traffic
does not continue to consume bandwidth on that branch. PIM-SM supports shared trees as
well as shortest path trees (SPTs). PIM-SM is beneficial for large networks that have group
members that are sparsely distributed.
and prune protocol, which means that multicast receivers, and the routers that support them,
must join multicast groups before they receive multicast traffic. When all receivers on a
network branch leave a multicast group, that branch is pruned so that the multicast traffic
does not continue to consume bandwidth on that branch. PIM-SM supports shared trees as
well as shortest path trees (SPTs). PIM-SM is beneficial for large networks that have group
members that are sparsely distributed.