Originally Posted by
rthonpm
The issue isn't with the IP of the DNS server changing, but rather with the clients that report back to the server changing their IP's.
Put simply: when your computer gets an IP from DHCP, it also reports to the internal DNS servers to say that hostname X now has IP address Y.
Your local machine also caches some DNS records for easy recall, and then checks back to the DNS server at a regular interval (usually around 90 minutes) for any changes to that cached copy.
Let's say that a number of devices go offline that are purely DHCP. When they come back up, they may not pull the same address. Your computer stayed up the whole time and still knows just the old IP addresses since it isn't time for a new cache check. In and instance like this, you either need to manually flush the DNS cache on the local computer to pull a new copy with the updated addresses (which requires admin rights), or you need to wait until the next DNS refresh. In a sufficiently large environment, neither of these options is really that good of a choice. This is why things like DHCP reservations exist, to allow devices to always pull the same address with no need to manually configure the device. For things like a workstation that are more or less a client system (i.e. it accesses other resources) straight DHCP is fine. For any resource that other access (i.e. it's serving something), you want to ensure that it's readily and predicatively available so you want it to have some kind of well known address.
If you're going to use DHCP for setting up devices: get a reservation for the IP. If you're going to use a static IP, don't use one in the range of addresses that DHCP doles out. The difference between the two generally comes down to how long it will stay around: printers get replaced much more frequently than servers so a DHCP reservation makes sense since it's plug it in, let it get an address, then lock it down as a reservation in the DHCP console of choice.
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