 involves the router interface's OSPF priority. The default priority is 1, which is the lowest value an interface can have and still be elected the DR. A value of 0 indicates Specific Routing Protocols that the router is ineligible to become the DR on the network. Setting the priority higher increases the chances that the router will be elected the DR. The OSPF interface priority is configured using the interface command ip ospf priority. The valid range is 0-255. Ideally, you should plan which router is to become the DR and set its priority accord- ingly. Usually, there is an obvious choice, such as a hub or core router, or perhaps just the most powerful router on the network. The designated router will be doing more work than the other routers, SO it should be the one with the most horsepower. If your design includes a hub router, that router will need to be the DR, because it will be the center of the topology. If the OSPF interface priority is not set, resulting in a tie, the router will use the OSPF router ID to break the tie. Every router has an OSPF router ID. This ID can be configured manually with the router-io command. If the router ID is not configured manually, the router will assign it based on the IP address of the highest-numbered loopback address, if one is configured. If a loopback address is not configured, the router ID will be the highest IP address configured on the router. The only ways to change the router ID are to remove and reinstall the OSPF configuration or to reboot the router. Be careful, and think ahead when planning your network IP scheme. When first deploying OSPF, engineers commonly make the mistake of neglecting the priority and router ID when configuring the routers. Left to its own devices, OSPF will usually pick routers that you would not choose as the DR and BDR. A common network design using OSPF is to have a WAN in the core as area zero. Figure 10-12 shows such a network. Notice that all of the areas are designated with the same OSPF process number. Each area borders on ar