Router acts like a sniffer

[b.shoresh]

Hello.

Can I define a certain FastEthernet interface on a router to act like a sniffer in a sense that it will collect into the router all the frames running on the LAN (not just broadcasts, multicasts,and unicasts that are carrying its own mac-address as the destination mac-address) ?

Thank you.

[rfroom]

The router can collect *some* of the information by debugs and CLI commands, but it should not be used as a sniffer. It is not a function of the router to copy packets to its ethernet port but rather a function of the switch.

[kschung]

As crazy as it may seem, I think you can force a 2500 router interface into promiscuous mode and collect RMON stats. There are probably other routers that support fast ethernet interfaces that you can do that to. While I wouldn't recommend it in a production environment, it has its uses in the lab.

[b.shoresh]

Thank you all for the answer.

What is the command to force the router's interface into promiscuous mode ?