what would be a sign of half duplex - question i had on ccna exam

carl_townshend · ‎06-17-2010

Hi all

I had a question on the exam, about what could indicate a half duplex issue on a port, it said which one of these would tell you there was an issue

bytes input

bytes output

giants

runts

there was one more but I can remember, would any of the above tell you if the port was in half duplex ?

cheers

Kevin Brennan · ‎06-17-2010

Hi Carl,

Runt frames could very well be a sign of half-duplex or indeed mis-matched duplex settings.

The runt can occur as a result of a collision or a faulty nic.

Was the other option you had a collision?

HTH

Kevin

carl_townshend · ‎06-17-2010

Hi

Thanks for the reply, I was suprised to see there were not collisions on there!

I thought a runt was a frame smaller than 64bytes ? How would this indicate a collision had occured ?

cheers

Carl

Kevin Brennan · ‎06-17-2010

Hi Carl,

A runt is a frame less than 64bytes in size. It's what can be left over after a collision.

I think (and I'm sure I'll be corrected if I'm wrong!) that a "normal" collision is detected when the frame fails the FCS. A runt is detected as being something that doesnt even have a FCS to test.

HTH

Kevin

glen.grant · ‎06-17-2010

You will be guaranteed to see collisions and possibly late collisions in a half duplex environment.