I have a PC running Ubuntu 11.04 with 2 nics. eth0 is internet and eth1 in Internal Lan. eth0 is connected to the internet talks and receives the correct DHCP addresses from ISP. I can from this computer ping the DNS servers at my ISP, I can ping www.google.com and any other sites so the DSN's are working fine. I have a dhcp server on the lan side that serves up the ip addresses to my computers connected to the internal lan. I have a firewall between the two nics (eth0 and eth1). This computer is also the gateway for my internal lan computers to access the internet.
What is more baffling is that any lan side computer (these are different flavours of Operating Systems i.e. ubuntu 10.04, Mac snow leopard, windows xp) all work fine, they can get to browse the internet using a range of browsers (firefox v3.6.22, safari, & ie) but here is the problem - the gateway computer can't browse the internet - this is the one that is running ubuntu 11.04, firefox 6.0.2. it also has a problem with even the ubuntu software centre which it can't download programs.
Help is needed and it would be greatly appreciated, I've tried the usual stuff that is recorded on the forums like ipv6 etc. But all my other computers go through this one and they have no problems - it must be something to do with ubuntu 11.04. very puzzling... please help. cheers JJ