Restrictions On Pim Dense Mode State Refresh; Information About Pim Dense Mode State Refresh; Pim Dense Mode State Refresh Overview; Benefits Of Pim Dense Mode State Refresh - Cisco Catalyst 3850 series Configuration Manual

Restrictions on PIM Dense Mode State Refresh

Restrictions on PIM Dense Mode State Refresh
• All routers in a PIM dense mode network must run a software release that supports the PIM Dense Mode
• The origination interval for the state refresh control message must be the same for all PIM routers on

Information About PIM Dense Mode State Refresh

PIM Dense Mode State Refresh Overview

The PIM Dense Mode State Refresh feature is an extension of the PIM Version 2 multicast routing architecture.
PIM dense mode builds source-based multicast distribution trees that operate on a flood and prune principle.
Multicast packets from a source are flooded to all areas of a PIM dense mode network. PIM routers that receive
multicast packets and have no directly connected multicast group members or PIM neighbors send a prune
message back up the source-based distribution tree toward the source of the packets. As a result, subsequent
multicast packets are not flooded to pruned branches of the distribution tree. However, the pruned state in
PIM dense mode times out approximately every 3 minutes and the entire PIM dense mode network is reflooded
with multicast packets and prune messages. This reflooding of unwanted traffic throughout the PIM dense
mode network consumes network bandwidth.
The PIM Dense Mode State Refresh feature keeps the pruned state in PIM dense mode from timing out by
periodically forwarding a control message down the source-based distribution tree. The control message
refreshes the prune state on the outgoing interfaces of each router in the distribution tree.
Related Topics
Configuring PIM Dense Mode State Refresh, on page 381
Originating Processing and Forwarding PIM Dense Mode State Refresh Control Messages Example, on
page 383
Processing and Forwarding PIM Dense Mode State Refresh Control Messages Example, on page 383

Benefits of PIM Dense Mode State Refresh

The PIM Dense Mode State Refresh feature keeps the pruned state in PIM dense mode from timing out, which
saves network bandwidth by greatly reducing the reflooding of unwanted multicast traffic to pruned branches
of the PIM dense mode network. This feature also enables PIM routers in a PIM dense mode multicast network
to recognize topology changes (sources joining or leaving a multicast group) before the default 3-minute state
refresh timeout period.
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3.6E (Catalyst 3850 Switches)
380
State Refresh feature to process and forward state refresh control messages.
the same LAN. Specifically, the same origination interval must be configured on each router interface
that is directly connected to the LAN.
IP Multicast Optimization: PIM Dense Mode State Refresh
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