How to control multicast within one same Lan ?

[wfqk]

Hi All, usually we send multicast streaming through router. If we just send multicast within one same lan, how can we control the traffic ? Any one can give some suggestion or link? Thank you

[Jon Marshall]

If you want to control traffic within a vlan ie only send multicast to those hosts that want it then you need two things -

1) IGMP snooping enabled which it usually is by default

and

2) something to make the IGMP queries. If you enable PIM on the L3 interface that would do it but PIM is only needed when you want to route multicast between subnets.

So most switches supports something called an IGMP snooping querier which makes the IGMP queries that IGMP snooping listens to.

Jon

[wfqk]

Thank you for your reply. If the end router is connected with a switch which is connected with many user PCs. All PC are in the same vlan. If only one PC request multicast streaming, other PC do not want to receive, do you think other PC still can receive multicast ?  

[Jon Marshall]

That is what I meant by the above.  

That is what IGMP snooping on a switch together with something to make the IGMP queries does ie. it records the multicast mac address against the ports.

So only the PCs that want the multicast stream are sent it.

Jon

[wfqk]

So, all we need to do is to configure CGMP at the router port which connects to the switch, do you think so ? Thank you.

[Jon Marshall]

CGMP is not used much now, it has been replaced by IGMP snooping.

I'm not sure what you are asking because I have explained that if you do not need to route the multicast stream you need IGMP snooping and the IGMP snooping querier feature.

The router would not need anything because you are only talking about multicast within a vlan.

If the multicast stream was being routed then you would still need IGMP snooping but you would not need the IGMP snooping querier because you would have enabled PIM on the router interfaces and then the router would send IGMP queries.

Jon

[wfqk]

Hi Jon Thank you so much for your explanation. Due to you reply and some document i read, my understanding is usually we do not need to configure IGMP snooping in this situation because IGMP snooping is usually enable by default. So, let's assume that there are two hosts, pc1 and pc2 are connected with the switch in the same subnet, pc1 needs multicast streaming and pc2 does not. As long as pc1 join the group, pc1 can receive the multicast streaming. Since pc2 does not join, it cannot receive the multicast streaming. Do you agree ? 

[Jon Marshall]

I don't know how to explain this any more clearly than I originally did.

IGMP snooping alone is not enough but I have said that two times already.

Please reread my original reply.

Jon

[wfqk]

It requires PIM etc commands between routers, but in my last reply, I was just talking about configuration of the switch connecting to the end router. Just with the switch, we usually do not need to use additional command for controlling multicast streaming in the switch because the switch IGMP snooping is enabled by default, do you think so ? If not, what command do you think we can use for the purpose in the switch ? Thank you for your nice reply.

[Jon Marshall]

I was just talking about configuration of the switch connecting to the end router. Just with the switch

That is what I have been talking about all along but perhaps I misunderstood your original question.

I thought your original question was about multicast in just one vlan ie. the multicast wasn't being routed so there is no PIM configuration.

If so IGMP snooping is not enough as per my original reply.

If you mean the multicast stream is being routed into the vlan and you have PIM enabled on the L3 vlan interface then IGMP snooping is enough and you do not need to configure anything else.

Jon