Blade ICE G8124 Manuale Utente

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  Chapter 20: OSPF

BMD00220, October 2010

When an OSPF routing device encounters traffic for a destination address it does not recognize, 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 G8124 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 

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.

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 (Router OSPF mode): 

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 configured 
metric value and metric type.

The OSPF default route configuration can be removed with the command:

RS G8124(config-router-ospf)#

RS G8124(config-router-ospf)#