Multicast for Dummies?

[AdmanOK]

I am trying to configure multicast on my network. I have Cisco 3662 routers at both my sites connected via an ATM network. I have added the following commands at each end.

[tt]
ip multicast-routing
!
interface FastEthernet0/0.1
description Data Vlan
ip pim dense-mode
!
interface FastEthernet0/0.2 - This is where my multicast stream is generated
description Voice Vlan
ip pim dense-mode
!
interface ATM3/IMA3.1 point-to-point - WAN interface to other site
ip pim dense-mode
pvc 3/103
encapsulation aal5snap
[/tt]

I am primarily trying to get multicast packets from the Voice VLAN on one site into the voice VLAN at the other site. I don't really care if they are also sent into the data VLANs. The same commands are added on the equivalent interface at the remote site, however the Multicast traffic is not present. What am I missing?


Compromise: Where I don't get what I want, but I'm happy because you didn't either.

 

[jneiberger]

Have you turned on IGMP on the FastEthernet interfaces at the other site? If your stream is being generated at one site, this still does you no good if you don't have devices that are successfully using IGMP to join the stream.

 

[AdmanOK]

Here's what I'm actually trying to achieve:

A device at Site A is broadcasting an RTP audio stream to the multicast address 239.1.1.1 on port 16384.

Other devices at Site A can listen to that adress and port and play the stream.

I would like devices at Site B to be able to listen to that same address and port and hear the audio stream.

I have tried messing with different settings, but I just can't make it work!

 

[jneiberger]

You're on the right track. Make sure you have multicast routing (PIM) turned on at Site B, as well, but you also need to have IGMP configured on the Ethernet interfaces on the router at Site B so those devices can successfully join the multicast stream.

PIM won't help you by itself. You need IGMP, as well. You may also need to turn on IGMP snooping on your switch or use CGMP, in which case that needs to be turned on at the router and switch.

HTH,
John

 

[ADB100]

If you enable PIM on an interface it automatically enables IGMP, there is no need to enable it unless you have specifically disabled it previously.
I would check your routers have correctly created state for the multicast group:

show ip mroute

You should see S,G and *,G for the 239.1.1.1 group in all routers.

HTH

Andy

 

[jneiberger]

Is it common practice to configure PIM on LAN interfaces? Back when I was doing multicast I only used PIM on the WAN interfaces and specifically configured IGMP on the LAN interfaces.

 

[ADB100]

PIM Must be configured on all the interfaces you wish to send multicast over, whether these be directly connected to senders & receivers or not.

Andy

 

[jneiberger]

Geez, I need to brush up on my multicast routing. It's been a while (like 4 years) since I needed to know it. I *thought* I was remembering correctly.