Multicasting- Sparse vs. Dense

cdad2000

Happy New Year Everybody,

I'm confused b/c ciscopress says one thing and Transcender says another. Is sparse multicasting widely dispersed or Dense? Thanks for your help, again.

dtlokee

I am not sure what you mean by dispersed but dense mode uses a flood and prune method of finding the receivers on the network. Dense mode assumes there are receivers on most subnets (or all subnets) and does not scale well because of the flood and prune method. Sparse mode requires the receivers to explicitly join the multicast tree before the muulticast traffic is forwarded to them. As the name implies this works better where the subnets are "sparsely populated" because it removes the overhead of flooding and pruning every 3 minutes

GT-Rob

To answer your specific question, PIM-SM, or sparse mode.

networker050184

I have always used sparse-dense mode as thats how I learned to implement it.

cdad2000

Thanks, for all your help. PIM-SM is more effective, then PIM-DM.

dtlokee

networker050184 wrote:

I have always used sparse-dense mode as thats how I learned to implement it.

That was the primary method of implementing multicast when you used auto-rp to advertise the RP because by its nature auto-RP required the auto-RP messages (which are multicast) to be dense mode flooded (this resulted in a catch 22 if it was only sparse mode because we needed a RP to find the RP). With the introduction of the "ip pim autorp listener" command you can run the whole network in sparse mode thereby reducing the bandwidth required by dense mode flooding and pruning. Alternatly you can use something like BSR which is carried in the PIM messages themselves.