Because of what the network can be stupid - data transfer 10mb / sec?

Question

System administration

Hello.
Guru help needed.
There is a network of 50 computers and two servers,
the first server is on esxi version 6 (it runs a domain controller (2008R2) and 1c (in 2003))
on the second file dump (2008R2)

there are 4 D-link switches in the rack (models 1510 and 1210 )

On that week, the problem began with the fact that the data transfer rate in the network dropped to 10mb
On the switches, they did not make any settings, they work by default.
In the logs there is nothing like kretichnogo.

The question is, this problem arises if something is shitting into the network and you need to find the source by disconnecting everyone from the switch and gradually connecting? (or are there any other options)

and the second question, can this situation be due to a domain controller?

And give advice on how to win or start calculating such garbage on the network!

When I find a problem, I promise to unsubscribe!

Answer 1

Is the wiring damaged? Switches and NICs can automatically slow down when the link quality is poor due to a physical line failure.

Answer 2

1) Did the speed drop throughout the network or only in some parts of it?
2) 10mb is megabits I hope?
3) it's not because of the controller for sure

Answer 3

What speed do clients show in connection settings?

Answer 4

The speed decreases and sometimes the connection even disappears when the wave impedance of the twisted pair changes. The cables are damaged somewhere, or the sockets / connectors may be clogged beyond the standards. In violation of the rules