Strange behaviour between a 10G interface and 1G interface

[l.buschi]

Hi all,

I have a stack of 3850 made by 1 switch full multigigabit copper interface and 1 switch full 1Gb copper interface.

My server are connected to 10GB interface.

I have the following problem: If I connect any host with 1GB nic to a 10GB RJ-45 port, it correctly negotiates 1GB interface but download from the server is very slow. I also tried to force the 10G interface to fixed 1G but nothing changes.

If I connect the same host to a 1GB native port of the same stack, download is perfect. 

Both the port 10G and 1G are configured same way:

switchport mode access

switchport access vlan 100

spanning-tre portfast

this happens with any computer with 1 GB Nic. (OS W8.1 or W10 or Server2012R2).

As I have a backup stack perfectly equal to the one I'm testing, I tried the same tests even in the second stack. the result is the same: download very slow if I connect to a 10G interface (negotiated to 1 G) and dowbload perfect if I connect to a native 1G interface of the same stack).

Any idea?

Tks for support.

Johnny

[Leo Laohoo]

I want to see if you're seeing any Total Output Drops on the interface.

[l.buschi]

It depends.

In some test I can find output drops, in other test I can't see any drop.

I Have an open cisco TAC case on this situation. They didn't find any configuration error nor any evident hardware problem.

They took my config file in order to try to reproduce the situation in their lab.

[Leo Laohoo]

What IOS-XE version are you running?

[l.buschi]

16.3.7

Same problem I had with 16.3.6