4 device mirror troubleshooting, Evice, Irror – PLANET XGS3-24042 User Manual
Page 614: Roubleshooting

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Switch(config)#monitor session 4 source interface ethernet 1/0/15 access-list 120 rx
69.4 Device Mirror Troubleshooting
If problems occur on configuring port mirroring, please check the following first for causes:
Whether the mirror destination port is a member of a TRUNK group or not, if yes, modify the TRUNK
group.
If the throughput of mirror destination port is smaller than the total throughput of mirror source port(s),
the destination port will not be able to duplicate all source port traffic; please decrease the number of
source ports, duplicate traffic for one direction only or choose a port with greater throughput as the
destination port. Mirror destination port can not be pulled into Isolate vlan, or will affect mirror between
VLAN.