"copying" packets to an interface to allow sniffing

What is the easiest way to “copy” packets to an interface so I can place a traffic sniffer there and sniff the data? If there any ay to say “if a packet comes in do all the normal stuff, but additionally output it on interface Y”?


When troubleshooting some aplication issues I’d like to be able to sniff the data in detail.

Tools - Packet Snffer, setup streaming, and grab that stream with Wireshark

Thanks; I finally had the time to test this and it works great with a system plugged directly into the router (not so great connected through switches, but that’s because the switches are being “helpful” and not passing on all the “unneeded” frames)