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Configuring Router-Port Group Management Protocol
RGMP Overview
IPC-530
Cisco IOS IP Configuration Guide
Figure 90 RGMP Messages
The router sends simultaneous PIM hello (or a PIM query message if PIM Version 1 is configured) and
RGMP hello messages to the switch. The PIM hello message is used to locate neighboring PIM routers.
The RGMP hello message instructs the switch to restrict all multicast traffic on the interface from which
the switch received the RGMP hello message.
Note RGMP messages are sent to the multicast address 224.0.0.25, which is the local-link multicast
address reserved by the Internet Assigned Numbers Authority (IANA) for sending IP multicast traffic
from routers to switches.
If RGMP is not enabled on both the router and the switch, the switch automatically forwards all
multicast traffic out the interface from which the switch received the PIM hello message.
The router sends the switch an RGMP join <G> message (where G is the multicast group address) when
the router wants to receive traffic for a specific multicast group. The RGMP join message instructs the
switch to forward multicast traffic for group <G> out the interface from which the switch received the
RGMP hello message.
Note The router sends the switch an RGMP join <G> message for a multicast group even if the router is
only forwarding traffic for the multicast group into a switched network. By joining a specific
multicast group, the router can determine if another router is also forwarding traffic for the multicast
group into the same switched network. If two routers are forwarding traffic for a specific multicast
group into the same switched network, the two routers use the PIM assert mechanism to determine
which router should continue forwarding the multicast traffic into the network.
The router sends the switch an RGMP leave <G> message when the router wants to stop receiving traffic
for a specific multicast group. The RGMP leave message instructs the switch to stop forwarding the
multicast traffic on the port from which the switch received the PIM and RGMP hello messages.
42759
PIM hello
PIM-SM
RGMP
RGMP
IGMP Snooping
RGMP hello
All multicast packets
RGMP join <G>
Multicast packets for group <G>
RGMP leave <G>
Multicast packets for group <G>
RGMP bye
All multicast packets
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