Speed negotiation in interface Gigabit

[tranminhc]

Hi forum,

I have a question about speed negotiation process between interfaces. I have 3650X Sw and 2960S-48port. All ports of two are GigabitEthernet, however the link between them is only 100Mb/s, Full duplex. I try to set the speed 1000 Mb/s manually in the interface then the interface never up. Its status is down/down. I must set back to speed auto.

I show interface Gigabit0/24 in Sw 3650-X and figure out that there are many output drop (over 600000). I clear counter then after two days the output drop is over 70000. This link is trunk link between two switches, all ports of access SW are Gigabit and connect to PC.

First, I thinks the 3650X is throttled somewhere in  output direction of trunk link. But there is another trunk link (Gi0/23) to another 2960S-48port and no output drop number in this interface. This Giga 0/23 speed is 1000 Mb/s (auto speed, auto duplex)

Does any outside things impact the speed negotiation process between 2 interfaces? And output drop number may caused by abnormal speed between two Gigabit interface?

I am trying to descible my trouble. Sorry to unclearly you guy somewhere. Any idea would be appreciated

Thanks

[Leo Laohoo · Accepted solution]

however the link between them is only 100Mb/s, Full duplex. I try to set the speed 1000 Mb/s manually in the interface then the interface never up. Its status is down/down. I must set back to speed auto.

If you are talking about copper links, then the patch cable you are using to link the two is possibly faulty.

The best way to determine is to run a TDR test.

I am suspecting Pair "D" is not working.