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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 22 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.
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Route summarization: When redistributing routes from other protocols as described in the
“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 all the
redistributed routes included in a specified network address and mask.
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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.
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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 determined 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.
