Once upon a time we had a home network illustrated below. On the network side, the DNS modem's IP is set to 192.168.0.1 and the only other member to that subnetwork is the router. On the other side of the router, I defined the network beginning with 192.168.1.1 (netmask 255.255.255.0). All computers in the network are assigned IPs that are a part of this network. I reserved and manually set the IP of our networked computer to 192.168.1.200. Everything was wonderful in this network garden of Eden.
Then, one day, we added a voice over IP (VOIP) device to the network. The printer no longer worked. So, fiddling with our one winD'OH!s machine,
I booted up my FreeBSD machine and checked what IP was assigned to it. In *nix, this task definitely is trivial. The assigned IP was not of the expected 192.168.1.x format. It was 10.0.0.x. Well, that explained something. I was able to log into the router by using 10.0.0.1. Sure enough, the router defaulted to this IP class in order to prevent the obvious conflict with the new VOIP device.
Now that I was in the router setup, I defined the home network side of the router to be 192.168.2.1 and I manually set the printer IP to 192.168.2.200. Everything works again without having to think about what's going on automatically in the background. Yay!
If you understand this business, wave.