Let's not forget to mention the 10,000 dialup customers who have to change their DNS numbers. We have sent snail-mail and e-mail over and over again, yet only about 1/3 of that 10k have actually made the change away from the old numbers. How many of those customers do you think we'll lose when we officially turn off the old ip's?
Keep a /32 route internally for your old DNS server numbers for a couple of years. Your customers will still see it, though noone else will. Of course your entire customer base will possibly lose connectivity to (1/2^32) of the internet - but they'd probably prefer that to losing their nameservers. If you want to be really cunning set the nameservers on the old box to resolve www.yournetworkname.net at a different server, which has a big notice to change their nameservers, plus a downloadable executable to go and do it for them on most operating systems. Presumably you are handing out dynamic DNS by radius in any case, which overrides the built in settings which copes with 95% of users. -- Alex Bligh GX Networks (formerly Xara Networks)