3Com 4500G Family Configuration Manual page 36

Features
Mirroring
Port mirroring copies packets passing through a port to another port
connected with a monitoring device for packet analysis to help implement
network monitoring and troubleshooting.
Traffic mirroring is implemented by a QoS policy, which defines certain
match criteria to match the packets to be mirrored and defines the action
of mirroring such packets to the specified destination. This document
describes:
Port Mirroring overview
Local port mirroring configuration
Remote port mirroring configuration
Traffic mirroring
Description