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

Unanswered Question
Jun 17th, 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



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


I have this problem too.
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Kevin Brennan Thu, 06/17/2010 - 02:22

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?



carl_townshend Thu, 06/17/2010 - 03:40


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 ?



Kevin Brennan Thu, 06/17/2010 - 03:48

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.



glen.grant Thu, 06/17/2010 - 05:16

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


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