3Com 5500-EI PWR Reference Manual page 821

A copy of each packet passing through a source port will be sent to the corresponding
destination port.
Related commands: display mirroring-group.
When you configure mirroring source port on an Ethernet port of a Switch 5500-EI, if
mirroring group 1 does not exist, the switch will automatically create local mirroring group
1 and add the source port to the group; if mirroring group 1 already exists, but is not a local
mirroring group, your configuration of the source port will fail.
Examples
# In Ethernet port view, configure Ethernet 1/0/1 as the source port, and mirror all packets
received on and sent from this port.
<Sysname> system-view
System View: return to User View with Ctrl+Z.
[Sysname] interface Ethernet 1/0/1
[Sysname-Ethernet1/0/1] mirroring-port both
monitor-port
Syntax
monitor-port
undo monitor-port
View
Ethernet port view
Parameters
None
Description
Use the monitor-port command to configure the destination port in Ethernet port view.
Use the undo monitor-port command to remove the configuration of the destination port
in Ethernet port view.
Note that:
You cannot configure a member port of an aggregation group, a fabric port, a member
port of an aggregation group, or a port enabled with LACP and STP as the mirroring
destination port.
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