mroute table

[suthomas1]

We have a 3750 acting as the core. By default IGMP snooping is enabled on cisco 3750 from the documents.

but, when we see the ip mroute table on the switch, it doesnt show any output.

what could be the cause. Thanks in advance!

[Raju Sekharan]

Hi

IGMP Snooping is for layer 2 multicast

You will see mroute entry, only if you have configured multicast-routing and the router is performing multi-cast routing

Thank you

Raju

[suthomas1]

so is ip multicast-routing command needed on the switch for enabling this. Will this command have any other impact as the switch in in active network.

Thank you.

[Raju Sekharan]

Hi

You need ip multicast-routing only if this device is doing multicast routing

You need to have PIM and RP configurations for IP Multicast routing

But check what is your requirement

Thank you

Raju

[suthomas1]

rp address configuration is in place. should the pim be under required interfaces or is it necessary ?

[John Blakley]

You'll need to have "ip pim sparse-mode" or "ip pim sparse-dense-mode" configured under the vlan or routed port interface in order to see any entries in your mroute table.

HTH,

John

[Raju Sekharan]

Hi

You need to have ip pim spare-mode configured if you have RP configured

Thank you

Raju

[suthomas1]

will configuring ip pim have any impact on the existing network?

[Raju Sekharan]

Hi

Configuring pim should not create any impact. This will make pim relation with neighbors and will allow the router to request multicast traffic from the upsteram routers

Thank you

Raju

[suthomas1]

the interface configuration only gives the option of ip pim passive and does not indicate usage of spare or dense mode with pim.

what could be the trouble here.

[Raju Sekharan]

Is this  layer 3 interface?

Thank you

Raju

[suthomas1]

yes , it is a layer 3 SVI interface.

please suggest.

[Raju Sekharan]

Are you running IP Base image?

The IP base image contains only PIM stub routing.  The IP services image contains complete multicast routing. On a switch  running the IP base image, if you try to configure a VLAN interface with  PIM dense-mode, sparse-mode, or dense-sparse-mode, the configuration is  not allowed.

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_53_se/configuration/guide/swmcast.html

Thank you

Raju

[suthomas1]

will the pim stub feature allow the multicasting to work or the sparse-dense mode is required.

Thanks.

[suthomas1]

so if the correct image is running, only need is to configure sparse-dense mode on the correct interface and enable mroute.

With this will the multicast work from one vlan to another within the same enterprise.