418 Dell PowerConnect 55xx Systems User Guide
FILE LOCATION:  C:\Users\gina\Desktop\Checkout_new\Maintenance Projects\Dell 
Contax\CxUGSwitching_Ports.fm
DELL CONFIDENTIAL – PRELIMINARY 9/11/12 - FOR PROOF ONLY
Port Mirroring 
Switches usually only forward frames to relevant ports. To monitor traffic, 
either for information gathering, such as statistical analysis, or for 
troubleshooting higher-layer protocol operation, the Mirroring feature 
forwards frames to a monitoring port.
Mirroring provides the ability to specify that a desired destination (target) 
port will receive a copy of all traffic passing through designated source ports.
The frames arriving at the destination port are copies of the frames passing 
through the source port at ingress, prior to any switch action.
It is possible to specify several source ports to be monitored by a single target 
port. However, in this case, the traffic sent to the target port is placed in the 
target port's queues on a first come, first served basis, and any excess traffic is 
silently discarded. This may mean that the traffic actually seen by any device 
attached to the target port is an arbitrarily selected subset of the actual traffic 
going through the source ports.
Port mirroring is only relevant to physical ports. Therefore, if you want a LAG 
to function as the source of a port mirroring session, the member ports must 
be individually specified as sources.
Up to four sources can be mirrored. This can be any combination of four 
individual ports.
Before configuring Port Mirroring, note the following:
• Monitored ports cannot operate faster than the monitoring port.
• All Rx/Tx packets should be monitored to the same port.
Destination Port Restrictions
The following restrictions apply to destination ports:
•
Destination
 ports cannot be configured as source ports.
•
Destination
 ports cannot be a member of a LAG.
• IP interfaces cannot be configured on the 
destination
 port.
• GVRP cannot be enabled on the 
destination
 port.
•The 
destination
 port cannot be a member of a VLAN. 
•Only one 
destination
 port can be defined.