Thanks for your input fukawi1.
This is on a laptop running Ubuntu 11, not a server. It is not acting as a router. There are no other rules. It couldn't be simpler.
I realize reading the man pages and such that this seems to be for a routing (net.ipv4.conf.all.forwarding = 1), but I want iptables on this host to mangle its own destination IP from 188.8.131.52 to 184.108.40.206.
The situation is something like this, but not quite. Say you have a website at 220.127.116.11, but there are links in the html that, instead of providing a relative reference, specify the IP address incorrectly as 18.104.22.168. Well, the links won't work because the IP is wrong. But if I fake my developers laptop out to go to 22.214.171.124 whenever 126.96.36.199 is specified then it will work. This isn't the real scenario, but gives you the idea.
The thing is, I did this years ago for another situation. It may be that they way iptables works has changed since then. Or maybe I actually did it on a server acting as a linux router. But it seems like this should be able to be done on a host.
---------- Post added 10-04-11 at 11:57 AM ----------
Oh, and I tried specifying protocol, etc. It still didn't work.