multicast/directed broadcast

[r.crist]

Easy questions.. I have a layer-2 network comprised of a 3550-12, 3550-24, and a 4006. The 3550-24 and 4006 are connected to the 3550-12 via Gig-E. All one broadcast domain, not routers on the network. Question 1: Is there anything I need to configure on the switches for multicast to work properly? Second question: should the switches handle directed broadcast frames differently than they handle multicast frames? My understanding is that the switches will handle the multicast and directed broadcast frames in pretty much the same manner: flood them to all ports except the source port. Thanks, Rich

[a.awan]

Multicast will not require any additional configuration to work, however, in your configuration you are correct in stating that the multicast and directed broadcast frames will be handled in the same manner. To ensure an effective deployment of multicast i would recommend using either igmp snooping or cgmp; igmp snooping is preferable since it is a standard and not a proprietary feature.

[r.crist]

Thanks for the reply. If we were to add a second vlan and configure routing on the 3550-12, I'd need to configure igmp/cgmp on the respective switch platforms, and configure multicast routing on the router. Just to clarify, though.. In our case, even if ip igmp snooping was disabled on the 3550-12, multicast forwarding would not be affected?

[a.awan · Accepted solution]

CGMP would require a router, however, IGMP snooping feature does not require presence of a router to be enabled. I know IGMP makes more sense when there is a router involved but i think it will also be helpful to contain multicast forwarding even within a flat network provided the hosts are IGMP enabled.

To answer your question, yes multicasting forwarding will work even if IGMP snooping was disabled on your 3550-12 switch. IGMP snooping is just a means of preventing the multicast packets to reach hosts not listening to the multicast group.

[r.crist]

Perfect! Thanks for the replies. I appreciate the help. -Rich

[aashish.c]

hi

on 3550, be default IGMP routing is enabled. It also supports PIM with dense ,sparse and dense-sparse mode. Directed broadacst will be sent to a specific subnet.switch`s CPU will be member or all multicast and broadcast packets.

i think we can say both the packets will be handled in same manner.