In your previous mail you wrote: Perhaps. Certainly stable IP address is preferable to being constantly and needlessly renumbered all the time (although if the practice became more prevelant, the silver lining is that it would likely put an end to that abomination known as IP-address dependent license keys). => unfortunately not because one can answer you may use another abomination known as NATs (sorry Keith to use this dirty word :-). So for static installations such as Cable Modems and DSL lines, I agree with you, and I wish network providers would provide stable IP addresses. => I agree and there is no technical reason to stay with dynamic IP addresses. However, I much prefer DHCP plus DDNS to Mobile IP. With Dynamic DNS, the security model is well understood; I need only inform a single host with whom which I have a trust relationship --- the DNS server for thunk.org --- that the DNS address for my laptop should be changed to 1.2.3.4. => I disagree because in order to make your box quickly reachable after an address change you have to play with RR TTLs and DNS is *not* designed to behave well with short TTLs... With Mobile IP, the security model seems to be (in order to avoid triangle routing), => the key point is again inside the parenthesis: your concern is not about Mobile IP (as you can get a trust relationship with your home agent) but about routing optimization of Mobile IP. The other, is as near as I can tell, completely and totally hopeless as far as being practical or deployable. => and Mobile IP without routing optimization as a replacement or a complement to DDNS? Thanks Francis.Dupont@enst-bretagne.fr