Multicast (*,group) question

[mahesh18]

Hi everyone,

i was reading about multicasting and it says when we do sh ip mroute command we will see

(source,group) so here source is user PC who wants to join the multicast group  and Group is Destination multicast address like 239.x.x.x right ??

Second thing i need to know is that if it says like (*,group) or (*,239.5.5.55  what does it mean ?

thanks

mahesh

[jonathanaxford]

Hi Mahesh,

Not quite - the (Source,Group) specifies the Source of the Multicast stream and the IP address of the group. So if the Multicast Source was a server with an IP address of 192.168.1.20 and it was sending to Multicast group 239.5.5.55 then the entry would read:

(192.168.1.20,239.5.5.55)

The (*,G) entry indicates a shared tree multicast tree - all of the sources for the group are using the same RP.

My multicast is not that strong, so I can't explaion in any great detail!

There is an expanation on the difference between source and shared trees here, which may prove useful:

http://www.informit.com/articles/article.aspx?p=32100

Many thanks

Jonathan