Re: Is IGMP snooping the same as multicast?

Enabling multicast routing will allow subnets on the same router to receive
a multicast stream, also sourced on that router. To get multicast to got
between routers, you need to enable PIM (Protocol Independent Multicast).
It's pretty simple, see the following doc..

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a00800ca796.html


<1crazyrican@xxxxxxxxx> wrote in message
news:1194289368.015741.130500@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Nov 5, 12:53 pm, Oliver Garraux <olrben...@xxxxxxxxx> wrote:
On Nov 5, 12:24 pm, 1crazyri...@xxxxxxxxx wrote:

I was asked to enable multicasting on my network (4507R core, 3750G
distribution, 3560G access). I ensured IGMP snooping was enabled and
used a packet sniffer to check for activity such as joining and
leaving a session while using a chat program that uses multicast. I
saw the exepcted traffic and the application worked. Is this enough to
enable basic multicast support? or is there something more that is
needed? I had a look at the Cisco documentation but I see a lot of
information on IP Multicasting which I'm not sure is the same thing.

thanks

Have you configured multicast routing? Multicast routing is required
if you want to be able to multicast between subnets/VLAN's. IGMP
snooping lets the switches know which ports it needs to forward the
multicast traffic to (L2), whereas multicast routing is responsible
for getting the multicast traffic from the source to all of the
destination subnets (L3). Unless you already had multicast routing
enabled on your L3 switches you probably will not be able to send
multicast traffic from one VLAN to another. Try your chat program
with your client on a different subnet from the server and see if
multicast still works with it.

Oliver

Thanks for the explanation.
I have IP multicast-routing enabled at the core switch (4507R).
Since IGMP is enabled on my L2 switches I should be fine.
I will test the chat probram again and try disabling/enabling
multicast-routing to see what happens.




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