Routers default behavior for mulitcast traffic

[zafar_118]

Hello,

What is router's default behavior (without enabling multicasting) for multicast traffic? Does it drop or look routing table and forward it?

[syed kazim abbas]

Traditional IP communication allows a host to send packets to a single host (unicast transmission) or to all hosts (broadcast transmission). IP multicast provides a third scheme, allowing a host to send packets to a subset of all hosts (group transmission). These hosts are known as group members.

[zafar_118]

Hi Kazim,

Thanks for your response but i am looking for router's default behavior when it receives a multicast packet.

[MARK BAKER · Accepted solution]

Hi Zafar,

IP multicast routing is not enabled by default on routers that I am aware of. It would have to be enabled and configured to route multicast.

If the router is running a feature that listens to multicast like HSRP, EIGRP, OSPF...., it will only be listening on the interface where it is configured and processed by the router and not forwarded. The router would also be sourcing packets with the feature's destination multicast IP out the interface where it is configured.

To answer your question, the default behavior for a router when it receives IP multicast would be to ignore it if it wasn't to a multicast address that the router itself is listening for.

HTH

Mark