24-Port Layer 3 Switch Management Guide

M ULTICAST R OUTING
3-233
CLI – This example enables PIM-DM globally and displays the current
status.
Configuring PIM-DM Interface Settings
To fully enable PIM-DM, you need to enable multicast routing globally for
the router (page 3-219), enable PIM-DM globally for the router
(page 3-232), and also enable PIM-DM for each interface that will
participate in multicast routing.
Command Usage
• PIM-DM functions similar to DVMRP by periodically flooding the
network with traffic from any active multicast server (page 3-222). It also
uses IGMP to determine the presence of multicast group members. The
main difference, is that it uses the router’s unicast routing table to
determine if the interface through which a packet is received provides the
shortest path back to the source.
• Dense-mode interfaces are subject to multicast flooding by default, and
are only removed from the multicast routing table when the router
determines that there are no group members or downstream routers, or
when a prune message is received from a downstream router.
• The interface settings that control the prune and graft messages (i.e.,
prune holdtime) should be configured to the same values on all routers
throughout the network to allow PIM to function properly.
Command Attributes
• VLAN – Selects a VLAN interface on this router.
• PIM-DM Protocol Status – Enables/disables PIM-DM. (Default:
Disabled)
• Hello Interval – Sets the frequency at which PIM hello messages are
transmitted. Hello messages are sent to neighboring PIM routers from
which this device has received probes, and are used to verify whether or
Console(config)#router pim 4-302
Console#show router pim 4-308
Admin Status: Enabled
Console#