Cisco CCNP / BCMSN Exam Tutorial: Configuring CGMP On Routers & Switches

If a Layer Two switch does not the ability to walk have IGMP snooping, they will be able to run CGMP - Cisco Group Membership Protocol. CGMP allows the multicast router to work with the Layer Two switch to eliminate unnecessary multicast forwarding.CGMP will be, my cams , enabled on both the multicast router and, my cams , switch, but the router does all the work. The router will send Word and let the switch messages, my cams , as needed. PIM must be running, my cams , on the router interface to the switch for enabling CGMP, as you can see: R1 (config) # int e0R1 (config-if) # ip cgmpWARNING: CGMP requires PIM enabled on interfaceR1 (config-if) # ip pim sparseR1 (config-if) # ip cgmpWhen CGMP is first enabled on both the multicast router and switch, the router sends a cGMP Join message, informing, my cams , the switch that a multicast router is connected, my cams , . This particular CGMP Join group contains a Destination Address, my cams , (GDA) and from the 0000.0000.0000 MAC address of the sending interface. The GDA is used to identify the multicast group, so if this is, my cams , set to all zeroes, the switch knows that this is an introductory CGMP Join, so the switch know that the multicast router is online.The switch makes an entry in the MAC table that this router can be found outside the port that came on the cGMP Join. The router sends a cGMP Word to the switch every minute to serve as a keepalive.A workstation is connected to the switch port 0 / 5 now wants to join multicast group 225.1.1.1. Join the message is sent to the multicast router, but will first pass through the switch. The switch will do what you would expect it to do - read the source MAC address and an entry for the MAC address table as the port fast 0 / 5 if no entry is already there to make. (Remember, my cams , that the MAC address table is referred to as the CAM table or the bridging table.) The router receives the Join request and send a CGMP Join back to the switch. CGMP Join This includes both the MAC multicast group and the MAC address of the host address. Now the switch knows about the multicast group 225.1.1.1 and that one member of that group can, my cams , be found from the port, my cams , fast 0 / 5. In, my cams , the future, when the switch receives frames destined for that multicast group, the switch will not flood the frame as he would an unknown multicast. Instead, switch to a copy of the frame to each port that it knows leads to a multicast group.Two member of the great benefits of cGMP are the explicit Join and Leave Group messages. In, my cams , the next part of this BCMSN exam tutorial, we take a look at the Leave Group messages.Chris Bryant, CCIE, my cams , # 12,933, is the owner of The Bryant Advantage,, my cams , home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package and Ultimate CCNP Study Packages.You may also have RSS feed and visit his blog, updated several times daily with new Cisco certification articles,, my cams , free tutorials, and daily CCNA / CCNP exam questions! Details on the website.For a FREE copy of his latest e-books, "How To Pass The CCNA" and "How To Pass The CCNP", visit the website!, my cams , You can also free CCNA and CCNP exam questions every day! Pass the CCNP exam with The Bryant Advantage!