Maximum supported frame size
The IPv4 encapsulation of mirrored traffic adds a 54-byte header to each mirrored frame. If a resulting frame exceeds the MTU allowed in the network, the frame is dropped or truncated.
NOTE:
Oversized mirroring frames are dropped or truncated,
according to the setting of the [truncation] parameter
in the mirror command. Also, remote mirroring does
not allow downstream devices in a mirroring path to fragment mirrored
frames.
If jumbo frames are enabled on the mirroring source switch, the mirroring destination switch and all downstream devices connecting the source switch to the mirroring destination must be configured to support jumbo frames.