duplex and speed settings on a switchport

tyran.king · ‎09-28-2010

I had set the switchport to duplex full, speed 100 and the sh run int command only shows speed 100, but when I look inder show int, it comes back as full duplex and speed 100. In the past, I always set the speed 100 first then duplex full and I was able to see both commands in the config. Does the order of these commands make that much difference and is this port manually set to full duplex, speed 100 if I set the duplex prior to setting the speed of the port?

Jason Masker · ‎09-28-2010

You must set speed first. I think this is actually a CCNA exam question. The reason is that duplex is automatically auto if speed is set to auto. I think I have some combination of equipment and IOS in the past that actually complains if you try to set duplex before speed.

See this document (CCO required) http://www.cisco.com/en/US/customer/tech/tk389/tk214/technologies_tech_note09186a0080094781.shtml

Or, if you don't have a CCO, the pdf http://www.cisco.com/application/pdf/paws/10561/3.pdf

In Appendix E, it states:

5. Why do you receive the error message "Port 1/1 is in auto-sensing mode" when you attempt to set the duplex mode?
A: You receive this error because you need to manually configure the speed on a port before you can manually configure the duplex mode.