Hello!
You can use the follwing command on the router/switch:
monitor session 2 source "vlan or interface" "rx,tx,both"
monitor session 2 destination "interface"
*where I put " you can hit ? to see what options you have to configure there
on the destination interface you can connect a PC with a packet capture like Ethereal, Wireshark and capture all the packets that you need.
This is the simpliest solution!
Please tell me if you understand!
Cheers,
Calin