This gives the channel number of the physical port where a MAC entry was learned, but only when that port is both a plain port-type interface and is itself channelized, broken into sub-channels as on some optical or bonded interfaces; otherwise the field simply reads 0. An admin working with channelized ports, for instance subdividing a high-speed port into multiple logical channels for different services, needs this value to know exactly which channel a specific customer's traffic and its learned MAC addresses are actually using. A non-zero value like 3 on a channelized port would mean the MAC entry belongs specifically to channel 3, not the port as a whole.