Solved: Ubuntu 9.10 does not see my LAN

Since this issue gave me quite a headache over the weekend, and since I eventually solved it, I decided to share the solution on my blog to avoid that someone else may waste time as I did.

First of all, the environment: a laptop with Ubuntu 9.10 that can be connected by wire or wireless to a home LAN. The LAN is connected to the web by an ADSL router. Second, the problem: after an update the laptop could not connect anymore to the LAN. eth0 and eth1 were detected but no activity was possible: ping, connect, web browsing… I spent a lot of time on fora and at the end I solved the problem by using hints available in different places. Here is the result. Please, note that since there was no way to see the LAN I had to install packages directly from an USB flash drive.

STEP 1: uninstall the network manager

sudo apt-get remove --purge wicd network-manager network-manager-gnome
sudo update-rc.d NetworkManager remove
sudo apt-get autoremove

STEP 2: install wicd from flash drive

sudo dpkg -i wicd_1.5.9-2_all.deb

STEP 3: flush and recreate IP tables

sudo iptables -F
sudo iptables -X
sudo iptables -t nat -F
sudo iptables -t nat -X
sudo iptables -t mangle -F
sudo iptables -t mangle -X
sudo iptables -P INPUT ACCEPT
sudo iptables -P FORWARD ACCEPT
sudo iptables -P OUTPUT ACCEPT

STEP 4: activate the firewall

sudo ufw enable

Now the laptop can see the network, ping ip addresses, connect to servers, access Windows shares, browse the web. Note that I used the Uncomplicated Firewall ufw rather than Firestarter or GuardDog since it is easy to configure and gives no troubles.