I have a Cisco 3560 switch which is dropping some frames the frames that are dropped are seen in a SPAN session for the ingress port (monitor source) but not in a SPAN session for the egress It has a positive counter displayed with show controllers "Valid frames, too small" against the receive side of the ingress port.

I cannot yet find any Cisco references to define this value. The frames that are being dropped have a Wireshark-reported frame length of 214 octets.

Does anybody know of a reference where this value is defined? (or know what this value refers to)

1 Answer 1


From this link I can see:

The number of frames received on an interface that are smaller than 64 bytes (or 68 bytes for VLAN-tagged frames) and that have valid FCS values. The frame size includes the FCS bits but excludes the frame header bits.

Now, why this should show up for 214-bytes frames is hard to say. Is it possible that the frames matching against this counter are not the same ones you see on wireshark?

  • Thanks for that, I wonder is this the same as a runt, I always assumed a runt would have an invalid FCS. It is certainly possible that the frames matching this are not the ones I see in Wireshark. Either way I guess, the switch is duff. Either it's mis-reporting and dropping or it's dropping silently.
    – marctxk
    Dec 6, 2017 at 14:40
  • Runts are basically 'debris' from collisions. Those won't have a valid FCS. Maybe you have some bad equipment connected to this 3560, which is (for example) "forgetting" to pad small packets up to 64 bytes
    – mere3ortal
    Dec 6, 2017 at 16:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.