Igmp Helper - Cisco IE-4000 Software Configuration Manual

Configuring IP Multicast Routing
Information About Cisco's Implementation of IP Multicast Routing
In Figure 86 on page
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
Figure 86 PIM Stub Router Configuration
Source
200.1.1.3

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 (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
Command Reference.
Auto-RP
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.
Mapping agents periodically multicast the contents of their Group-to-RP mapping cache. Thus, all routers and switches
automatically discover which RP to use for the groups they support. If a router or switch fails to receive RP-discovery
messages and the Group-to-RP mapping information expires, it switches to a statically configured RP that was defined
with the ip pim rp-address global configuration command. If no statically configured RP exists, the router or switch
changes the group to dense-mode operation.
Multiple RPs serve different group ranges or serve as hot backups of each other.
679, Switch A routed uplink port 25 is connected to the router and PIM stub routing is enabled on
Configuring PIM Stub Routing, page 691
3.1.1.2.255.255.255.0
Router
for more information.
Switch
A
Port 25 Port 20
VLAN 100
Host 1 Host 2
679
Host 3
Cisco IOS IP Multicast