Absolutely correct. Real firewalls pass inbound traffic because a
state table entry exists. NATs do the same thing, with nasty
side-effects. There is no added security from the header-mangling.
--Steven M. Bellovin, http://www.cs.columbia.edu/~smb
To which Len Bosak quipped a few years ago: "If you don't know its name, you can't curse it".
Sean.
Sure you can. For a human entity, get a few hairs from its head or nail
clippings. For a network entity, get the bits of its externally visible
IP address.