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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter22 Configuring IP Unicast Routing Configuring OSPF
Switch# show ip ospf
Routing Process "ospf 1" with ID 172.20.135.202 and Domain ID 0.0.0.1
Supports only single TOS(TOS0) routes
Supports opaque LSA
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of opaque AS LSA 0. Checksum Sum 0x0
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
External flood list length 0
Area 1
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 1 times
Area ranges are
Number of LSA 1. Checksum Sum 0x83C2
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Other OSPF Behavior Parameters
You can optionally configure other OSPF parameters in router configuration mode.
•Route summarization: When redistributing routes from other proto cols as de sc ribed i n th e
“Redistributing Routing Information” section on page 22-57, 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 al l t h e
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 c ommon (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 1 0 by default,
and bandwidth (bw) is determined by the bandwidth interface configuration command. For multiple
links with high bandwidth, you can specify a larger number to di fferent ia te the co st on th os e l inks.
•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.