ZyXEL XGS4700-48F User Guide - Page 331

Chapter 36 OSPF When you configure an OSPF interface, you first set an interface to transmit OSPF traffic and add the interface to an area. You can configure a virtual link to establish/maintain connectivity between a nonbackbone area and the backbone. The virtual link must be configured on both layer-3 devices in the non-backbone area and the backbone. 36.1.4 OSPF and Router Elections The OSPF protocol provides for automatic election of Designated Router (DR) and Backup Designated Router (BDR) on network segments. The DR and BDR keep track of link state updates in their area and make sure LSAs are sent to the rest of the network. In most cases the default DR/BDR election is fine, but in some situations it must be controlled. In the following figure only router A has direct connectivity with all the other routers on the network segment. Routers B and C do not have a direct connection with each other. Therefore they should not be allowed to become DR or BDR. Only router A should become the DR. Figure 163 OSPF Router Election Example You can assign a priority to an interface which determines whether this router will be elected to be a DR or BDR. The router with the highest priority becomes the DR, while a router with a priority of 0 does not participate in router elections. In Figure 163 on page 331 you can assign a priority of 0 to routers B and C, thereby ensuring they do not become DR or BDR and assign a priority of 1 to router A to make sure that it does become the DR. 36.1.5 Configuring OSPF To configure OSPF on the Switch, do the following tasks: 1 Enable OSPF XGS4700-48F User's Guide 331