I have some recollection of that problem, but not the solution. It's actually somewhat topical for my client right now. You and Paul have told us about FreeBSD and Linux; is there also a Solaris equivalent? (probably not required as they're gradually upgrading it to Linux, but would be good to have).
As far as I know Solaris doesn't have accept filtering of any sort. But it has been a number of years since I cared about Solaris, so I could be wrong. A quick search didn't turn up anything obvious.
-Rasmus
