Hi, all, When I plug in a Cisco837 router into the swich, it gives me a warning message: CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on Ethe rnet0 (not half duplex).
When I do a "sh interface ethernet0", it shows: "Full-duplex,
The IOS is: 12.3(8). Is there anyway to change it to half duplex?
Thanks.
what switch are you plugging the router into and how is the port configured ?
find out if the switch is capable of 100-full or 10-full and set it accordingly
otherwise on the 837 try
ethernet 0 speed 10 duplex half exit
I had the same problem on an 837 and 2950 switch. IIRC, setting the duplex to half and speed to 10, still resulted in CDP duplex mismatch error, or collisions. I remember reading something about a CDP bug, so I just disabled CDP on that port.
ie (on 837) ethernet 0 no cdp enable exit
or (on switch) fastethernet 0/24 no cdp enable exit
under interface ethernet 0, I could not set it to half duplex. have to disable cdp. it worked. thank you very much guys.
Rather than disable CDP completely, you can issue the command:
no cdp log mismatch duplex
which just prevents the router reporting these errors.
I had the same issue. I fixed the speed on the 2950 end to 10Mbit/HD and it went away. A bit of reading on the Cisco site at the time led me to believe that the E0 port isn't full-duplex which is the bug. Rather, it's a virtual interface of the 4 Fa ports which aren't proper switchports unlike the 1800 series. Therefore, for simplicity, I treat it as a hub.
At half duplex collisions are OK and normal - if you see frame or other errors then you have a duplex mismatch.
none
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