Port forwarding with UFW

Kernels & Hardware, configuring network, installing services

Port forwarding with UFW

Postby Spivey » 2020-01-30 12:14

I'm trying to set up port forwarding, so pointing a web server from the public internet to port 8080 on machine A ( will access a web server on machine B ( on a private network. Machine A has a second interface on the private network, and masquerading from the private network to the internet is already working.

The symptom is that connections can apparently be made from the outside world to the desired port, but as soon as data is sent, the connection is closed:
Code: Select all
mike@flotsam:~$ telnet spivey 8080
Connected to spivey.oriel.ox.ac.uk.
Escape character is '^]'.
GET / HTTP/1.0
Connection closed by foreign host.

What's more, a similar experiment conducted on Machine A with "telnet 80" does succeed in retrieving a page from the web server.

Here are the rules I've written in /etc/ufw/before.rules:
Code: Select all
# NAT table rules

# Forward requests from port 8080 to new server
-A PREROUTING -i enp0s25 -d -p tcp --dport 8080 -j DNAT --to-destination

# Forward traffic through upstream ethernet

# don't delete the 'COMMIT' line or these nat table rules won't
# be processed

Added to that, I've set DEFAULT_FORWARD_POLICY="ACCEPT" in /etc/default/ufw. And of course IP forwarding is turned on in the kernel, or the masquerading from inside to outside wouldn't work.

What's wrong here?
Posts: 1
Joined: 2020-01-30 12:02

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