Jim Tanous over at the Mac Observer has a great post today about how to configure your Airport Extreme router for DHCP reservations. Why might you want to do this? For example, if you had a device in your home that you want to always be assigned the same internal IP address.
For example, I use this trick so that my Drobo FS has a constant IP address and I can use that IP address to mount it via AFP for file sharing purposes. The rationale behind this is a long story and perhaps another subject for another post. But I've found that manually mounting my Drobo via AFP rather than using the built-in Drobo dashboard software allows CrashPlan to see the Drobo's mounted drives and be able to backup data to and from them.
This trick can also be helpful for a home based file server, or as a troubleshooting technique when you have a device on your network that seems to drop connections.
The post is worth a read if nothing more for an understanding this option is available. Thanks Jim!