General Multicast question

[0r8it]

Hi there, a general question about the principles of multicast, for anyone that fancies having a crack at explaining it.

For the record, I've a scenario in mind:

I'm sending an audio stream by IP from a server to a workstation. Both devices are on individual Cisco switches (2900 series). Currently, this works well.

However, I would like to also send the same stream simultaneously to another machine, this time in a remote part of the building. I have some mmf fibre and another switch waiting, and plan to link the switch the existing workstation is on to the new switch via fibre.

Viz:

Existing config:-

(--- denotes Ethernet)

[SERVER]---[2950#1]----[2950#2]----------[PC1]

Proposed config:-

(--denotes copper ethernet, +++ denotes fibre)

[SERVER]---[2950#1]----[2950#2]----------[PC1]

_______________________+

_______________________+++++++[2950#3]---[PC2]

(Ignore the double lines, they're just there for padding.)

Assume for the time being that the server can only talk to one machine at a time. Can I configure 2950#2 to take an input on one port and send it out of 2 other ports at the same time?

I realise that port monitoring will give me something like a fix, but I'm really just interested in what multicast would do in this situation. If anyone wants to just point me to a link, I'd be happy with that.

All the best!

0r8it

[scottmac]

I don't know if you can do this, but it *might* work:

Try setting up a NAT device/process such that the unicast address coming from the server is "Network Address Translated" into a multicast address ... (224.0.0.0 - 239.255.255.255).

I'm not sure that NAT will allow a multicast address on the interface.

Might be worth a shot.

Scott

[djohnston]

Since you don't have a router, you won't have to do anything for the multicast steam to reach all devices. L2 switches floor multicast traffic. This assumes that all devices are in the same VLAN.

-Don

[mrbmchitlin]

If you can have your server send the audio stream to a multicast address, say 239.255.1.1 and if your PC player application is multicast aware, then by having both hosts listen to that stream will make it happen.

It will only be sent once by the app, the network does the rest.All 3 ports need to be in the same vlan and trunk between the switches.

As there is no router involved you will either need to statically tell both switches that these clients are attached to these ports, it will be an interface command like "ip multicast ?" or "ip igmp ?"

You can enable igmp snooping if your 2950 supports it, which means when the PC joins the stream the switch will intercept the igmp join and will be able to dynamically assign the stream to whatever port you attach to.

Take a look at

http://www.mrchitlin1.demon.co.uk/CCNP/Multicasting/IGMP.ppt

It's not published but is there, and don't sue me if you try it and break it.

[0r8it]

Thanks for all your answers, folks, I'll be labbing this all soon.

0r8it