How to handle ports/firewall with Debian Buster lxc?


Active Member
Jul 18, 2019
Hi guys

I have created a container based on a Debian Buster template to use as a VPN server.
The problem I have is that only port 22 is available towards that machine and I'm puzzled on how to solve this (fairly new to Proxmox/containers and Linux is not my strongest point)
My Proxmox installation had been redone recently, did not change anything related to firewalling.

I tried to open a port on the console of the lxc with:
iptables -A INPUT -p udp --dport <port number> --jump ACCEPT
If I check with "netstat -tulpen" that specified port is not listed.

Can someone please help me out on this?

iptables -A INPUT -p udp --dport <port number> --jump ACCEPT

If you haven't changed anything else inside the container, these rules are unnecessary, as the default policy for the filter->INPUT in Debian is already ACCEPT. Also, just FYI, iptables-save doesn't "save" the config anywhere, it just prints it so you can save it to a file manually, rules are automatically activated.

If I check with "netstat -tulpen" that specified port is not listed.

Yes, that's normal. 'netstat' doesn't show "open" ports, it shows ports where programs are actually listening. All ports are "open" by default, just no application is awaiting any communication. Is the VPN server you mentioned already running?

A quick way to demonstrate and test your connectivity is via python:

Run python3 -m http.server 4444 on your container, then access 'http://<container-ip>:4444' in a web browser. If you see a directory listing, port 4444/tcp (replace with whatever if you like) is open. Then, 'netstat' will also show port 4444 being "in use" on the container.
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Reactions: PeterZ
Hi Stefan, thanks for stepping in.

I have used other (bare bone) virtualisation platforms before but containers are new for me so it's not really clear how the interaction between the container and it's environment exactly works.
Therefor I was a puzzled whether this was a firewall issue, even-though the firewall settings seemed to be OK in the web interface.

Thanks a LOT!


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