multicast

Unanswered Question
Apr 1st, 2008

Hi all, can routers route multicast ? is this done by default and if so is it easy to set up ?

also if you do route it do you use a routing protocol or static ?

I have this problem too.
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legerity1_2 Tue, 04/01/2008 - 10:45

Carl,

You can definately route multicast traffic, but you'll need to enable PIM - multicast routing does not occur by default. There are two main modes of operation, sparse and dense. Usually, dense is used when a high % of your network needs to subscribe to the multicast stream. It's easy to configure but lately Cisco seems to be moving away from this model. Sparse is recommended on new installs(dense by default floods the network with the multicast streams and can cause some interesting issues).

The basic difference between sparse and dense is that dense automatically forwards the stream throughout the routing topology while sparse identifies a center or "rendezvous" point and sends the stream from there (it's not that simple, but thats the gist of it).

Here is a place to start:

http://www.cisco.com/en/US/tech/tk828/technologies_tech_note09186a0080094821.shtml

Is it easy? Depends on your install and what the multicast topology will look like. If you're routing over a hop or two, it shouldn't be too much trouble. However, large installations can take some thought and serious planning to do right.

HTH,

Geoff

carl_townshend Wed, 04/16/2008 - 02:04

Hi There

so, do we need to run a routing protocol for this or is there another way ?

karthick78 Wed, 04/16/2008 - 03:00

Hi,

No need of any routing protocol.You meed to enable ip multicast routing in global config

then in interface you have to mention which mode (Sparse or Dense )

Karthik

carl_townshend Wed, 04/16/2008 - 04:54

so if im a client on one end of my wan, and want to receive a stream from my server, how will the routers forward this? do they route the traffic ?

karthick78 Wed, 04/16/2008 - 19:35

Hi,

If you configured in Dense-Mode then it will forward to all the routers , the application listen to the particular multicast group (IP) .

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