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New Member

ip multicasting


I have a few questions at I needed some clarification on. At my location I was assigned a task to deploy IP Multicasting. I readed a few articles on the subject off your web site. I also read cisco press title IP MULTICAST DEPLOYMENT. After reading all this material I am confused about what to due about IGMP Snooping on catalyst 6500 platform with MSFC2 router modules on them. What I read in the cisco press book states I should enable CGMP because it is prefered over IGMP snooping. When I look at the Catalyst IOS Instruction on IP Multicast it is silent on the topic of CGMP. There is no mention of it at all, can you clear this issue up for me. Those ICGM Snooping cause extreme overhead on the catalyst platform.? We have Several Catalyst 5500 in our network what code level should I be at when connected to a Catalyst 6500 MSFC.

The second Question I have is the following. We have two catalyst 6500 at the distribution layer. Both 6500's are hsrp neighbor for user segments, On the users segments we have passive interface command in the EIGRP process to reduce excessive redundancy. Will the passive interface statement have an adverse affect on ip multicast reverse path forwarding?

The last question I have is the following; What is the advantage auto-rp has over BootStrap Routing protocol? Which is best to deploy in a total cisco shop and why? The Cisco press book just skimmed over this point, The book was a bit dated.

Any help you can provide me will be very greatly appreciated


New Member

Re: ip multicasting

1)Actually,the Catalyst 6000/6500 supports an enhanced version of cgmp known as igmp snooping.

The benefits of IGMP Snooping is that it does not support require an external router for CGMP processing and does not have the CGMP leave processing - HSRP limitation.

In addition, CGMP and IGMP Snooping in the same network also works seemlessly and the MSFC also supports CGMP processing to external switches.

In the ciscopress book, its given that CGMP is preferred over IGMP snooping because not all the catalyst switches support IGMP snooping.

Since Catalyst 6500 is layer 3 capable, it supports IGMP snooping.

You can refer the following document to find this information:

2)Regarding the second question, I think the command passive interface will not create any negative impact on ip multicast reverse path forwarding.

3)Cisco recommends to use Auto-RP if the whole network is made of Cisco routers but if you use devices of vendors other than cisco then its better to use BootStrap mechanism.

BootStrap Routing protocol is for PIMv2 and auto-RP can be used for PIMv1 as well as PIMv2.

A bootstrap router (BSR) provides a fault-tolerant, automated RP discovery and distribution mechanism.

Thus, routers dynamically learn the group-to-RP mappings.

Sparse mode and dense mode are properties of a group, as opposed to an interface.

A very useful link regarding this is:

New Member

Re: ip multicasting


Thanks for the attention. You confirm What I had floating in my mind. I have been doing further research and testing various configuration in my lab and found a document on IP ANY CAST to be very interesting. If you have reviewed this document, Can you share your insight with me. I was all set to go with the auto-rp configuration until I saw read this document. I am new to the multicast business and I do not what to cause more harm than good.

any suggestion you can provide me would be a great help.


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