HP ProCurve 6120G/XG Configuration Manual page 507

This command assigns a mirroring source to a previously
configured mirroring session on a source switch. It specifies the
port and/or trunk source(s) to use, the direction of traffic to
mirror, and the session identifier.
The no form of the command removes a mirroring source
assigned to the session, but does not remove the session itself.
This enables you to repurpose a session by removing an
unwanted mirroring source and adding another in its place.
interface < eth-port-list >: Identifies the port(s) or static
trunk(s), on which to mirror traffic. Use a hyphen for a
range of consecutive ports (d5-d8). Use a comma to
separate non-contiguous interfaces (d5,d8).
monitor all < in | out | both >: For the interface specified by
< port-list >, selects traffic to mirror based on whether the
traffic is entering or leaving the switch on the interface.
in: Mirror entering traffic.
out: Mirror exiting traffic.
both: Mirror traffic entering or exiting.
(Using monitor without mirroring criteria or session
number affects session 1. Refer to "Monitor Command" on
page B-46.)
Monitoring and Analyzing Switch Operation
Traffic Mirroring
B-37