I recently discovered the source of an intermittent problem I was experiencing on the network at home. When browsing the SMB network my PC would timeout and not find any other servers, though trying to go directly to those servers would succeed. I thought that the problem had something to do with firewalls but hadn't had time to investigate fully until earlier this week when my brother reported the exact same problem (except he was using Windows). The problem wasn't occurring for me, though when I turned off iptables on my PC his network browsing started to work again (after a reboot, but then it was XP after all...). An investigation with smbclient (using the -L option) revealed that my PC had managed to get itself elected master browser, and of course iptables was then blocking all the broadcast traffic which SMB uses to build browse lists.