Periodically socket not opened between two debian machines?

Question

Nginx

Hello!
There are two Debian machines. One acts as a client, the other as a server.
Recently, a problem has appeared: about once out of five to ten (in the test out of 925 attempts, 87 times the socket was not opened), the socket is not created, and it crashes with a timeout (error 110).
At the same time, it does not matter how to create / catch a socket (php, c ++, java were tested) - the problem is present.

The most interesting thing is that if one of the machines is replaced (that is, used as a client or server by something else), then the problem disappears.
Therefore, the problem only exists between these two machines.

What could be the reason? Where to dig?
Thank you for your responses!

Answer 1

For a discount, it would be worth digging towards the kernel settings, in particular the network subsystem. It's trite to see how many connections are hanging and in what states with netstat.