In networks where a Layer 2 switch interconnects several routers, such as an Internet exchange point (IXP), the switch floods IP multicast packets on all multicast router ports by default, even if there are no multicast receivers downstream.IGMP snooping will not help but what is not clear that if there is no igmp message received on ports connected to routers why still switch will forward the traffic to router port and there is no downstream recievrs as well.
Can you be please more specific what you mean by writing: "When you enable pim on a interface, that interface will automaticly do an igmp join to all groups." As far as I know, until you use the "ip igmp join" command on a router interface, the router does not send IGMP joins. Actually, that is why the RGMP had to be invented.
This is incorrect it will not do automatic join when u enable pim then what is the use of ip igmp join-group and static-group
Moreover my question if both routers in the lan has upstream interface(wan) to source they why the traffic is copied back throgh L2 switch by the DR to the peer router interface which ultimately gets dropped due to RPF check failure and igmp snoop in the switch doesn't help.
I was a little bit too quick, and unclear, in my previous answer.
The router don't do a join, instead the switch will detect that a router exist on the port when the router sends out either a igmp querier or a pim hello.
Because of that the switch adds the router port to the outgoing portlist for all mcast groups. As a result of this the router will receive all mcasttraffic that excists in the switch.
This can be viewed by "sh ip igmp sno mro" and "sh ip igmp sno gro"
To overcome this rgmp can be used, then the switch will use rgmp-info to decide what ports to send mcast-traffic to, and routers that don't have receivers can signal to the switch that they don't want to receive that traffic.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...