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Alteon OS Application Guide
Chapter 12: OSPF
19742C4911, January 2007
Default Routes
When an OSPF routing device encounters traffic for a destination address it does not recog-
nize, it forwards that traffic along the default route. Typically, the default route leads upstream
toward the backbone until it reaches the intended area or an external router.
Each GbE Switch Module acting as an ABR automatically inserts a default route into each
attached area. In simple OSPF stub areas or NSSAs with only one ABR leading upstream (see
Area 1 in Figure 12-3), any traffic for IP address destinations outside the area is forwarded to
the switch’s IP interface, and then into the connected transit area (usually the backbone). Since
this is automatic, no further configuration is required for such areas.
Figure 12-3 Injecting Default Routes
If the switch is in a transit area and has a configured default gateway, it can inject a default
route into rest of the OSPF domain. Use the following command to configure the switch to
inject OSPF default routes:
In the command above, <metric value> sets the priority for choosing this switch for default
route. The value none sets no default and 1 sets the highest priority for default route. Metric
type determines the method for influencing routing decisions for external routes.
When the switch is configured to inject a default route, an AS-external LSA with link state
ID 0.0.0.0 is propagated throughout the OSPF routing domain. This LSA is sent with the con-
figured metric value and metric type.
>> # /cfg/l3/ospf/default <metric value> <metric type (1 or 2)>
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