Known bugs:

1) NAT in the OUTPUT chain only works since kernel 2.4.18.  However,
   there is a patch for previous kernels 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).

4) When you use ip6tables packet mangling on IPv6 packets, the packet will
   not be re-routed in case e.g. you insert a routing header.