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Multicast Configuration?

Hello

My multicast knowledge is basic, I understand the concepts but have not done a huge amount of configuration.

Anyway, we have a system a CCTV system which uses multicast for the video streams.

The 'sender' for want of a better word and the 'recievers' are on the same Vlan and that Vlan has a Routable SVI on the distribution switch.

The distribution switch has IP 'Multicast Routing Distributed' enabled but I was expecting to see some additional PIM commands on the SVI for that Vlan??

interface Vlan555

description CCTV

ip address 10.1.1.1 255.255.255.0

One of the Access Switches which has cameras in Vlan555, has the following configured:

ip igmp snooping querier address 10.1.1.1

Is multicast setup correctly using these commands?

I was expecting to see something like:

interface Vlan555

description CCTV

ip address 10.1.1.1 255.255.255.0

ip pim dense-mode

Many Thanks

1 ACCEPTED SOLUTION

Accepted Solutions
New Member

Re: Multicast Configuration?

If you only need the traffic to stay in the local vlan then you don't need to have PIM commands on the Layer3 interface. In the old days, you needed PIM on the layer3 interface to get the IGMP queries to go into the subnet. The switch would hear the IGMP queries and mark the incoming port as the IGMP mrouter port.

This had the downside of having to enable L3 multicast which wasn't always desired. However, you can now configure a querier on the layer2 switch and the switch can send queries out without the layer3 interface being involved. This satisfies the IGMP snooping as kind of a replacement mrouter port, more or less. The IGMP queries go out and the hosts respond. The hosts on the ports that need to hear the local vlan multicast traffic stay as receiver ports since they respond to the IGMP queries. The snooping does the rest. I used to do this on 6509's and it worked quite well but this was a few years ago.

As usual, its best to check current documentation but the layer 2  querier command should work.

You should be able to do a show ip igmp groups and see which multicast group IP(s) and ports are active.

4 REPLIES
Bronze

Multicast Configuration?

My knowledge of multicast at the primary level, but at the time helped me a lot in practice next article

http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a008059a9df.shtml

So,

you have a working configuration by Solution 2: Enable IGMP Querier Feature on a Layer 2 Catalyst Switch

you expect to see by Solution 1: Enable PIM on the Layer 3 Router/VLAN Interface

p.s 'd love to hear more knowledgeable colleagues on this issue...

New Member

Re: Multicast Configuration?

If you only need the traffic to stay in the local vlan then you don't need to have PIM commands on the Layer3 interface. In the old days, you needed PIM on the layer3 interface to get the IGMP queries to go into the subnet. The switch would hear the IGMP queries and mark the incoming port as the IGMP mrouter port.

This had the downside of having to enable L3 multicast which wasn't always desired. However, you can now configure a querier on the layer2 switch and the switch can send queries out without the layer3 interface being involved. This satisfies the IGMP snooping as kind of a replacement mrouter port, more or less. The IGMP queries go out and the hosts respond. The hosts on the ports that need to hear the local vlan multicast traffic stay as receiver ports since they respond to the IGMP queries. The snooping does the rest. I used to do this on 6509's and it worked quite well but this was a few years ago.

As usual, its best to check current documentation but the layer 2  querier command should work.

You should be able to do a show ip igmp groups and see which multicast group IP(s) and ports are active.

Multicast Configuration?

Spot on James, thank you.

I was unaware of the IGMP Querier process but having now read up on it, it makes sense

New Member

Multicast Configuration?

It's quite useful. There are a lot of times where you only need multicast at layer2 vlan and don't need any layer3 multicast routing.

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