Duplexing hassles with Cat1900s

[ElGreco]

Hi there guys

I'm currently running a whole rack of cisco cat 1900s (the ports are all forced to full duplex) which are connected to a cat 3648. The problem I am having is not so much on the switching side of things, but more on the client side. The Clients are running accton en1208 (10 Mbits Full duplex) and En166MX2 (10 Mbits Full duplex). Clients are complaining that their file transfer rate is particularly slow. Upon investigation we found that forcing the 1900s ports to half duplex drastically improved performance, with the clients nics still running at 10Mbits full duplex. We also tried forcing the clients onto half duplex and the switch to full and we achieved the same optimum performance.

Could someone explain this notion to me please.
Full duplex is Bidirectional data flow
Half duplex is Unidirectional data flow
That I understand. But surely if both client and switch are running at full duplex 10 Mbits, optimum performance should be achieved and not the other way round.

Strange?
Any ideas?

Regards
ElGreco

 

[thekidcisco]

Well, this is a top 10 Issue on CCO's Lan Switching.

There has consistenly been problems with duplex and speed associated from the host to the switch ports. Generally manually setting the port and speed instead of using autonegotiation has seemed to solve the problems.

Since the autonegotiation protocol will vary from NIC vendors and the changes in CatOS/IOS will also have an impact on the autonegotiation protocols as well, so there will never be compatibility here (I doubt anyway).

These are useful commands for checking the port settings:

show port (stat)
show mac

These will show you the errors reported on the interfaces connecting to your hosts. If your errors such as FCS etc are high then most probably it is a speed/duplex mismatch b/n the switch and the hosts.