The problem I encountered here is weird. There are two ubuntu linux machines, two identical HTTP servers run on them. One is ok on port forwarding, the other gets ERR_EMPTY_RESPONSE.

I've checked ufw settings but found nothing, since I can do SSH login on any of them, it should be enough for port forwarding. So, any suggestion to debugging this problem? Thank you in advance.

FYI, I did the test: On the server, Port forwarding is 64444:localhost:64444.

# nc -vv -l 64444 // Got nothing.

On the client, run:

# nc -vv localhost 64444 myhost [] 64444 (?) open sent 0, rcvd 0: NOTSOCK

# nc -vv localhost 64441 // any other port myhost [] 64441 (?): connection refused sent 0, rcvd 0: NOTSOCK


Oh! I see the problem.

In one server, /etc/ssh/sshd_config has the line below that will drop forward connection directly.

AllowTcpForwarding no

After I remove this line and restart sshd, this problem is solved.

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