My problem is this. We currently use BellSouth with an ip range 66.x.x.x and we are switching to a new wan provider with a range of 64.x.x.x . I have a pix firewall with a website and email sever on the inside. Obviously the current DNS at BellSouth is set to point to the current ip's for my website and mail server. When we switch the website and mail server will be at new ip addresses.
I have heard it can take up to 72 hours for the new DNS to propagate throughout the net. So does this mean my website and mail will fail when I reprogram my firewall to the new ip range, if so how do I avoid having them go down during that 72 hour period.