[Darkflame808]

Most routers keep a list of mac addressed connected in the past to ensure the same pc will get the same ip but after a certain period of inactivity, the mac is purged from the router and the IP is reassigned to the next device to connect to it.

If its critical you have access to your server, static is the way to go. Saves you the headache of having to reopen all your ports for RDC, BT, Games, Etc.

I have a static internal ip set and I use no-ip for the external dns as my provider changes my external ip every few days-weeks.