Quick Reference Guide

692 PowerConnect B-Series TI24X Configuration Guide
53-1002269-02
Configuring OSPF
23
Modify administrative distance
Layer 3 Switches can learn about networks from various protocols, including Border Gateway
Protocol version 4 (BGP4), RIP, and OSPF. Consequently, the routes to a network may differ
depending on the protocol from which the routes were learned. The default administrative
distance for OSPF routes is 110. Refer to “Changing administrative distances” on page 777 for a
list of the default distances for all route sources.
The router selects one route over another based on the source of the route information. To do so,
the router can use the administrative distances assigned to the sources. You can bias the Layer 3
Switch decision by changing the default administrative distance for RIP routes.
Configuring administrative distance based on route type
You can configure a unique administrative distance for each type of OSPF route. For example, you
can use this feature to prefer a static route over an OSPF inter-area route but you also want to
prefer OSPF intra-area routes to static routes.
The distance you specify influences the choice of routes when the Layer 3 Switch has multiple
routes for the same network from different protocols. The Layer 3 Switch prefers the route with the
lower administrative distance.
You can specify unique default administrative distances for the following route types:
• Intra-area routes
• Inter-area routes
• External routes
The default for all these OSPF route types is 110.
NOTE
This feature does not influence the choice of routes within OSPF. For example, an OSPF intra-area
route is always preferred over an OSPF inter-area route, even if the intra-area route distance is
greater than the inter-area route distance.
To change the default administrative distances for inter-area routes, intra-area routes, and external
routes, enter the following command.
PowerConnect(config-ospf-router)# distance external 100
PowerConnect(config-ospf-router)# distance inter-area 90
PowerConnect(config-ospf-router)# distance intra-area 80
Syntax: distance external | inter-area | intra-area <distance>
The external | inter-area | intra-area parameter specifies the route type for which you are changing
the default administrative distance.
The <distance> parameter specifies the new distance for the specified route type. Unless you
change the distance for one of the route types using commands such as those shown above, the
default is 110.
To reset the administrative distance to its system default (110), enter a command such as the
following.
PowerConnect(config-ospf-router)# no distance external 100