Cisco 3845 Software Guide - Page 596

Configuring OSPF Chapter 29 Configuring IP Unicast Routing Use the no form of these commands to remove the configured parameter value or to return to the default value. Configuring Other OSPF Parameters You can optionally configure other OSPF parameters in router configuration mode. • Route summarization: When redistributing routes from other protocols as described in the "Using Route Maps to Redistribute Routing Information" section on page 29-97, each route is advertised individually in an external LSA. To help decrease the size of the OSPF link state database, you can use the summary-address router configuration command to advertise a single router for all the redistributed routes included in a specified network address and mask. • Virtual links: In OSPF, all areas must be connected to a backbone area. You can establish a virtual link in case of a backbone-continuity break by configuring two Area Border Routers as endpoints of a virtual link. Configuration information includes the identity of the other virtual endpoint (the other ABR) and the nonbackbone link that the two routers have in common (the transit area). Virtual links cannot be configured through a stub area. • Default route: When you specifically configure redistribution of routes into an OSPF routing domain, the route automatically becomes an autonomous system boundary router (ASBR). You can force the ASBR to generate a default route into the OSPF routing domain. • Domain Name Server (DNS) names for use in all OSPF show privileged EXEC command displays makes it easier to identify a router than displaying it by router ID or neighbor ID. • Default Metrics: OSPF calculates the OSPF metric for an interface according to the bandwidth of the interface. The metric is calculated as ref-bw divided by bandwidth, where ref is 10 by default, and bandwidth (bw) is specified by the bandwidth interface configuration command. For multiple links with high bandwidth, you can specify a larger number to differentiate the cost on those links. • Administrative distance is a rating of the trustworthiness of a routing information source, an integer between 0 and 255, with a higher value meaning a lower trust rating. An administrative distance of 255 means the routing information source cannot be trusted at all and should be ignored. OSPF uses three different administrative distances: routes within an area (interarea), routes to another area (interarea), and routes from another routing domain learned through redistribution (external). You can change any of the distance values. • Passive interfaces: Because interfaces between two devices on an Ethernet represent only one network segment, to prevent OSPF from sending hello packets for the sending interface, you must configure the sending device to be a passive interface. Both devices can identify each other through the hello packet for the receiving interface. • Route calculation timers: You can configure the delay time between when OSPF receives a topology change and when it starts the shortest path first (SPF) calculation and the hold time between two SPF calculations. • Log neighbor changes: You can configure the router to send a syslog message when an OSPF neighbor state changes, providing a high-level view of changes in the router. Beginning in privileged EXEC mode, follow these steps to configure these OSPF parameters: Step 1 Step 2 Command configure terminal router ospf process-id Purpose Enter global configuration mode. Enable OSPF routing, and enter router configuration mode. 29-30 Cisco ME 3800X and 3600X Switch Software Configuration Guide OL-23400-01