Idea to think about: --salt 3b5b91c5a2 XOR client addresses for some more privacy
the salt can be added e.g. when restarting router/iptables or may be generated for
a particular host once. Purpose: hide MAC addresses behind the address mapping
gateway 

Check compat with tcpdump. Linux2.4 needs to copy skb() for that, but it oopses

Update csum, see http://www.firstpr.com.au/ip/ivip/checksums/ and
http://www.faqs.org/rfcs/rfc1624.html