Configure a mirroring session on the source switch

To configure local mirroring, only a session number and exit port number are required.

If the exit port for a mirroring destination is on a remote switch instead of the local (source) switch, you must enter the source IP address, destination IP address, and UDP port number for the remote mirroring session. You may also wish to enable frame truncation to allow oversize frames to be truncated rather than dropped.

Frames that exceed the maximum size (MTU) are either dropped or truncated, according to the setting of the [truncation] parameter in the mirror command. Frames that are near the MTU size may become oversize when the 54-byte remote mirroring tunnel header is added for transport between source switch and destination switch. (The addition of the header is a frequent cause for frames becoming oversize, but note that all oversize frames, whatever the cause of their excess size, are dropped or truncated.) If a frame is truncated, bytes are removed from the end of the frame. This may cause the checksum in the original frame header to fail. Some protocol analyzers may flag such a checksum mismatch as an alert.


Note that if you enable jumbo frames to allow large frames to be transmitted, you must enable jumbo frames on all switches in the path between source and destination switches.