The new network-manager package in Intrepid messed up my firewall (managed by Firestarter) by connecting to the wired and wireless network at the same time. The solution for me: Gufw.
When I got to the office after I upgraded Ubuntu to the 8.10 release, I could not log in on one of our servers, not a single web page loaded and I wasn’t even allowed to ping to other machines. Disconnecting the network cable and using the wireless connection made everything work again.
After spending some time where I found out that the wired network wasn’t to blame, I asked our sysadmin for help. It appeared that the network manager in Intrepid (version 0.7) connects to both the wired and wireless network if it can. This doesn’t have to be a problem though. All traffic was routed via the wired connection. So that wasn’t the problem.
What took me a while to figure out was that I used Firestarter to manage the firewall for my wireless connection. (I tend to connect to WLANs at customers, train stations, etc. And since I’m too lazy to manage which ports my laptop listens to, I just want to block all incoming traffic.) Since I installed it a while ago and it just worked, I had forgotten all about it.
I don’t know the exact details, but apparently Firestarter, correctly, saw that I had a wireless connection and it blocked all traffic via the wired connection. But that was the default route… Disabling the firewall solved the problem so the culprit had been found.
Unfortunately, I could not figure out how to get Firestarter to behave. It has been a while since I configured a firewall manually and I really didn’t fancy diving into the iptables documentation. I therefore decided to use the Uncomplicated Firewall topped off with Guwf for easy configuration.
Installation and configuration was a breeze. After using your favourite tool to install packages, you can find Gufw via System, Administration, Firewall configuration. All I needed to do was enabling it and making sure it was configured to deny incoming traffic. As an extra I also allowed SSH access since I regularly want to copy stuff to and from other machines. That was it; I’m all set again.