You *can* set a cookie to an IP address.
You just cannot wildcard it! So while -domain=>'.289.11.63.71' is invalid, -domain=>'289.11.63.71' is not
(get rid of the period before the first set of numbers).

This has got to be allowed for one reason: what of servers that are located on a machine without a domain?
You have to be able to set cookies somehow!
Also, the only way to specify "subdomains" of an IP address is through port numbers.
It is apparently possible using HTTP::Cookie or the Set-Cookie2 header, but I have been unable to restrict a cookie to a specific port :(