Multicast vs. Broadcast frames

RIP2 can run "compatibility mode" where it uses broadcasts rather than m/cast.

adevice with a reasonable interface chip can program the chip with the set of multicast MAC addresses it is interested in, and ignore the rest in hardware.

All broadcasts traditionally need the CPU to examine each packet to decide whether to ignore it.

some layer 2 switches can use multicast control to limit where the packets go within a subnet, reducing the average bandwidth overhead per port.

doesnt matter for a few packet / sec for RIPv2, but once you start sending multiple 5 Mbps MPEG2 video on multicast it gets more important......

Yaron -

On a single segment like you mention, there isn't really that much of a difference - other than the address that a packet is multicast to or broadcast to (multicast will always be in the range of 224.0.0.1 -

When you get to multiple segments or even multiple subnets, then you get into the real guts of multicast and how it works. Because then, communication between nodes and network devices allows a multicast server application (such as an Anti-virus app) to send feeds to only the hosts who need them. A multicast group can exist with a single multicast host on every subnet in a large vlan environment and each of those hosts (and only those multicast hosts) will receive the server's traffic.

This is a quick and dirty high-level overview, but I hope it helps. The Cisco Press books "Routing TCP/IP" volume 1 & 2 are good books with a large section on multicast.

Thanks for your answer, much appriciated.

V. Evans:

server's

Thank you stephen, great response.

stephen:

CGMP or IGMP snooping on Catalyst Switches.