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If a Layer Two switch does not have the capabilities to run IGMP Snooping, it will be capable to run CGMP - Cisco Group Membership Protocol.  CGMP makes it possible for the multicast router to operate with the Layer Two switch to eradicate unnecessary multicast forwarding.

CGMP will be enabled on both the multicast router and the switch, but the router's going to do all the work. The router will be sending Join and Leave messages to the switch as needed.   PIM should be running on the router interface facing the switch just before enabling CGMP, as you can see:

R1(config)#int e0

R1(config-if)#ip cgmp

WARNING: CGMP requires PIM enabled on interface

R1(config-if)#ip pim sparse

R1(config-if)#ip cgmp

When CGMP is very first enabled on both the multicast router and switch, the router will send a CGMP Join message, informing the switch that a multicast router is now connected to it. To study more, please consider peeping at: [[http://armorgames.com/user/hammerfog99|hammerfog99's Profile  Armor Games]].  This specific CGMP Join will contain a Group Location Address (GDA) of 0000.0000.0000 and the MAC address of the sending interface. The GDA is utilised to recognize the multicast group, so when this is set to all zeroes, the switch knows this is an introductory CGMP Join, letting the switch know that the multicast router is online.

The switch makes an entry in its MAC table that this router can be located off the port that the CGMP Join came in on.  The router will send a CGMP Join to the switch each and every minute to serve as a keepalive.

A workstation connected to the switch on port /5 now wishes to join multicast group 225.1.1.1.  The Join message is sent to the multicast router, but 1st it will pass via the switch. Identify further about [[http://www.generation-europe.eu/forum/activity/p/45462/|GEF Forum  yi  Activity]] by navigating to our ideal article directory. The switch will do what you'd anticipate it to do - study the source MAC address and make an entry for it in the MAC address table as getting off port rapidly /5 if there's not an entry currently there. For a different standpoint, please check out: [[http://www.plus.friendite.com/blogs/582562/1121011/how-to-find-wholesale-mortgage-l|FrienditePlus - Blog View - How To Find Wholesale Mortgage Lenders]]. (Never forget that the MAC address table is also referred to as the CAM table or the bridging table.)

The router will then acquire the Join request, and send a CGMP Join back to the switch.  This CGMP Join will include both the multicast group's MAC address and the requesting host's MAC address.  Now the switch knows about the multicast group 225.1.1.1 and that a member of that group is found off port rapidly /5.  In the future, when the switch receives frames destined for that multicast group, the switch will not flood the frame as it would an unknown multicast. To learn more, consider checking out: [[http://www.mya.co.uk/mya-space/members/nylon138jhet127/activity/614195/|intangible]]. Rather, the switch will forward a copy of the frame to every port that it knows leads to a member of the multicast group.

Two main benefits of CGMP are the explicit Join and Leave Group messages.  In the subsequent portion of this BCMSN exam tutorial, effectively take a appear at the Leave Group messages..