Multicast between VLANs

[mgoddard]

Hi,

We have roughly 10 VLANs configured on a 2948 Layer3 switch.

We need to enable multicast for the Symantec ghost application.

Currently we have the 'no ip directed broadcast' set against each fe interface but 'ip directed broadcast' enabled on each BVI. Ip helpers are used to allow DHCP/DNS requests.

Does this mean that IP multicasting is disabled between VLANs?

If so, is it as simple as enabling ip multicast and PIM on each BVI to allow the traffic through?

Thanks

Matt

[JASON WELCH · Accepted solution]

All you should need to do is enter 'ip multicast-routing' from global, then 'ip pim ' under each vlan SVI.

Thats how I have this config'd and it works fine for Ghost mcasting.

HTH,

Jason

[mgoddard]

Thanks for the quick replies.

It's the answer I was hoping for.

Would allowing multicast on each BVI have any down-sides, such as allowing a client PC to multicast between VLANs and cause problems?

If so, is this only resolved with access-lists?

Thanks

[JASON WELCH]

Once you turn on multicasting any host would be able to mcast unless you restrict via an ACL, as you described above. This wouldn't nessecarily cause any 'problems', but it does present a network management challenge, assuming that you don't want every host to be able to be a mcast server.

[Richard Burts]

Matt

In your question you describe where you prohibit ip directed broadcast and where you permit it. However directed broadcast does not have anything to do with propagating multicast.

If you want to propagate multicast between VLANs then you will need to enable ip multicast and to configure PIM on each interface where you want multicast propagated.

HTH

Rick