@nonpartisan said:
@BTrey said:
This normally happens is one side is set to auto and the other side is hard coded to full. Since one side is hard coded, it will not negotiate and the negotiation process fails. When the process fails, the autonegotating port goes to the most conservative setting - half duplex.
I knew that . . . I discounted that possibility since it was stated that it sometimes negotiated to full and sometimes not. Also, for a gig connection full duplex is the default by 802.3 standard whereas half is the default for 10/100. That's why I wondered if there was a speed negotiation issue too.
I hadn't even seen your response when I posted mine. First guess for "sometimes negotiated to full and sometimes not" is that some of the switchports were hard coded and some weren't. (It isn't clear whether "sometimes" means the same machine if you reboot it or different machines. I took it to mean that some of the machines came up correctly and some did not.) Another possibility is buggy drivers. We had an IOS upgrade on Cisco 3550s a couple of years back that caused all sorts of issues. After some time troubleshooting, we identified that one particular brand/model of NIC wouldn't properly autonegotiate with the switch and caused a duplex mismatch. Other brands and other modes of the same brand worked fine. Don't know if the bug was caused by Cisco or the NIC driver, but we ended up having to hard code both sides of the connection for all PCs with that model of NIC.