Comment 5 for bug 59331

I have had this exact problem, solved as you describe, in Ubuntu Feisty:

uname -a
Linux doris 2.6.20-15-server #2 SMP Sun Apr 15 07:41:34 UTC 2007 i686 GNU/Linux

An alternative solution is to install Firestarter, which I think works by using this iptables line:

sudo iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu