Known bugs: 1) NAT in the OUTPUT chain does not work in stock kernels. However, there is a patch in patch-o-matic, called the 'local-nat.patch'. This patch adds a CONFIG_NF_IP_NAT_LOCAL kernel config option. 2) tcpdump traffic is corrupted by OUTPUT NAT. 3) Connection tracking doesn't wait very long for reply FIN, meaning that half-closed pipes can time out early (seen frequently with squid).