Question about Cisco switches and manual vs. auto uplinks

ScottFern

What I have noticed is that sometimes certain uplinks between switches or between the router and the switch one end is set to manual 100/full and the other end is set duplex auto speed auto.

Now, between switches on uplinks and between switches and router links what is the best practices for this?

We were seeing bandwidth out the router at 6Mbps when we should of been seeing 90+ Mbps.

The part that tricked us at first was the ports would negotiate at 100/full but it took us a while to notice that one end was set manually while the other was set auto/auto. We couldn't understand why we were seeing such poor WAN performance and I guess that did the trick?

What is the Cisco best practices for this?

chmorin

ScottFern wrote: »

What is the Cisco best practices for this?

I'm pretty sure cisco wants you to tell the port what speed it should run at manually, and not use auto if you can avoid it. But I could be mis-reading your situation.

johnwest43

What matters most is that they match. If you set 1 to auto set the other to auto, if you set 1 to 100/mb full set the other to 100/mb full.

what can happen with 1 set to auto and 1 set to 100/mb full is that the auto side falls back to 10/mb half. that can lead to alot of droped packets and alot of latency. You might want to do a sh int | error to see if you had alot of dropped packets.