Set Int
Set Int”
If a Layer Two switch does not have the capabilities to run IGMP Snooping, will be able to implement good manufacturing practices – Cisco Group Membership Protocol. Good manufacturing practice allows the multicast router to work with the Layer Two switch to eliminate unnecessary multicast forwarding.
CGMP is enabled on the router and switch multicast, but the router do all the work. The router sends join and leave messages for change is necessary. PIM must be running on the router interface to the switch before enabling CGMP, as you can see:
int R1 (config) E0 #
R1 (config-if) # ip cGMP
WARNING: CGMP requires PIM enabled on interface
R1 (config-if) # ip pim low
R1 (config-if) # ip cGMP
When CGMP for the first time enabled the multicast router and switch, the router sends a message of good income Manufacturing, reports the switch of a multicast router is connected. This particular CGMP Join will contain a destination address of the group (GDA) of 0000.0000.0000 and MAC address of the sending interface. The GDA is used to identify the multicast group, so when it is set to all zeroes, the switch knows that is an introduction CGMP Join, letting the switch know that the multicast router is online.
The switch creates an entry in your table that MAC router is opposite the port that the CGMP Join came. The router sends a CGMP Join to the switch every minute to serve as a keepalive.
A workstation connected to the connection port 0 / 5 now wants to join the multicast group 225.1.1.1. Join the message is sent to the multicast router, but first through the switch. The switch had to do what we want – read the source MAC address and make a corresponding entry in the port MAC address table and off fast 0 / 5 if there is an entry already exists. (Remember that the MAC address table is also known as the CAM table or the bridging table.)
The router will then receive the Join request, and send a CGMP Join to the switch. This CGMP Join will contain both the group multicast MAC address and MAC address of the requesting host. Now the switch knows the multicast group 225.1.1.1 and a member of this group is a quick port 0 / 5. In the future, when the switch receives frames destined for this multicast group, the switch floods the frame of what would be an unknown multicast. Instead, the switch sends a copy of the framework for each port that you know leads to a multicast group member.
Two main advantages are the explicit CGMP join and leave group messages. In the next part of this BCMSN exam tutorial, we'll take a look at the conservation group messages.
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