Jmeter distributed testing. How to connect to a server behind NAT?

Question

SSH

When configuring distributed testing, I ran into a problem connecting remote servers located behind NAT.
The node with the jmeter client has an external ip, all servers (3 pieces) are in different networks behind NAT without the possibility of direct port forwarding.
Decided to try an SSH tunnel.
On server:

> jmeter-server -Djava.rmi.server.hostname=127.0.0.1
> ssh -N -f -R  55500:127.0.0.1:55500 -R 55501:127.0.0.1:55501 -L 60000:127.0.0.1:60000 [email protected]_node_ip -p 5000

On the client:

> jmeter -n -t testcase.jmx -l testcase.jtl -Djava.rmi.server.hostname=127.0.0.1 -r

The test passes successfully with a small number of simultaneous connections specified in the test case (10-100).
The problem appears when specifying a larger number of simultaneous sessions.
The SSH tunnel breaks, giving the following errors:

accept: Too many open files
open failed: administratively prohibited: open failed
Write Failed: broken pipe

If you look at ssh debugging, you can see that a huge number of connections are being created through port 60000, it seems that a new connection is created for each test request that the server must execute. Is this normal behavior?
ulimit is the maximum both on the server and on the client.
What could be the problem? Maybe someone had experience setting up jmeter through an ssh tunnel?