Only the nonredundant access router topology is supported by the PIM stub feature. By using a nonredundant
topology, the PIM passive interface assumes that it is the only interface and designated router on that access
domain.
In the following figure, Device A routed uplink port 25 is connected to the router and PIM stub routing is
enabled on the VLAN 100 interfaces and on Host 3. This configuration allows the directly connected hosts
to receive traffic from multicast source 200.1.1.3.
Figure 3: PIM Stub Router Configuration
Related Topics
Enabling PIM Stub Routing (CLI), on page 124
Example: Enabling PIM Stub Routing, on page 156
IGMP Helper
PIM stub routing moves routed traffic closer to the end user and reduces network traffic. You can also reduce
traffic by configuring a stub router (device) with the IGMP helper feature.
You can configure a stub router (device) with the ip igmp helper help-address interface configuration
command to enable the device to send reports to the next-hop interface. Hosts that are not directly connected
to a downstream router can then join a multicast group sourced from an upstream network. The IGMP packets
from a host wanting to join a multicast stream are forwarded upstream to the next-hop device when this feature
is configured. When the upstream central router receives the helper IGMP reports or leaves, it adds or removes
the interfaces from its outgoing interface list for that group.
For complete syntax and usage information for the ip igmp helper-address command, see the IP Multicast
Command Reference, Cisco IOS XE Release 3SE (Catalyst 3850 Switches).
Auto-RP
The PIM-SM protocols require the presence of a rendezvous point (RP) in the network. An RP acts as the
meeting place for sources and receivers of multicast data. If a static RP configuration is used, then the
configuration needs to be applied on all the routers in the multicast network. To automate this process, the
Auto-RP protocol was devised.
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3650 Switches)
OL-29890-01 117
Configuring PIM
IGMP Helper
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