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!
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
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.
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
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.
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
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.
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.
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.