Cisco Systems 3560 Manual De Usuario

The PIM stub feature is enforced in the IP base image. If you upgrade to a higher software version, the 
PIM stub configuration remains until you reconfigure the interfaces.

, Switch 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. See the 

 for more information.

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 (switch) with the IGMP helper feature. 

You can configure a stub router (switch) with the igmp helper help-address interface configuration 
command to enable the switch 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 

.

This proprietary feature eliminates the need to manually configure the RP information in every router 
and multilayer switch in the network. For auto-RP to work, you configure a Cisco router or multilayer 
switch as the mapping agent. It uses IP multicast to learn which routers or switches in the network are 
possible candidate RPs to receive candidate RP announcements. Candidate RPs periodically send 
multicast RP-announce messages to a particular group or group range to announce their availability.

Mapping agents listen to these candidate RP announcements and use the information to create entries in 
their Group-to-RP mapping caches. Only one mapping cache entry is created for any Group-to-RP range 
received, even if multiple candidate RPs are sending RP announcements for the same range. As the 
RP-announce messages arrive, the mapping agent selects the router or switch with the highest IP address 
as the active RP and stores this RP address in the Group-to-RP mapping cache.

Source

200.1.1.3

Router

3.1.1.2.255.255.255.0

Switch

A

Host 1

Host 2

VLAN 100

Host 3

Port 25

Port 20

202

3

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