ip igmp static-group
Donot Accept But forwards Multicast traffic
ip igmp join-group
Accepts and forwards Multicast traffic
I understood the meaning and behaviour of these two commands,
But What is confusing me is, WHY FAST SWITCHING IS PREVENTED WHEN "ip igmp join-group" IS USED. I read that "The static-group command causes the router to put the interface permanently in the OIF (output interface) list. This is not process-switched"
What is this mean? Hope you will shed some lights on this
>> why packets of group x.x.x.x are not sent to main cpu for processing if "ip pim igmp-join" is used and not for the "ip pim static-group"
I wrote sent to main cpu for ip pim igmp-join.
answering is difficult, my guess is that the two commands have different purposes:
the first one makes the router one of the receivers of group x.x.x.x and forwards the packets of the group out the interface where it is applied.
the second command only puts the interface in the OIlist but doesn't make the router a receiver for group x.x.x.x.
the command reference says:
for igmp join-group
>>IP packets that are addressed to the group address are passed to the IP client process in the Cisco IOS software.
This means becoming a receiver for a group.
To configure static group membership entries on an interface
if you have interest in testing source specific multicast you can notice that ip igmp join-group has no option to specify a source.
When I tested PIM SSM I used this:
Rx router with ip pim static-group with source option to generate the correct PIM SSM join for (S,G) downstream to this a second router Ry actually used as an host with ip igmp join-group to that same group G.
This to be able to ping group G using source S in a lab environment.
I think this explains clearly the difference between the two commands: Rx couldn't answer to a ping because it is not a receiver of (S,G).
Hope to help