Monday, April 30, 2012

Propagating Default Routes - OSPF

How to get default routes into OSPF routing domain? Well, there is really just about one way to do it. It is by using default-information originate.

Consider this simple topology below and follow the screenshots.

I am going to add a static default route to null0 and redistribute static into OSPF so we can see how this does not work as it does with EIGRP and other routing protocols.

First let's get some basic configuration taken care of such as interfaces and simple OSPF.

  • Configure a static default route to null0
  • Get into OSPF config mode and redistribute static subnets
  • Notice that R2 has a default route however, R3 does not have a default even though we are redistributing static route into OSPF  
  • Get into OSPF configuration mode
  • default-information originate <options> 
  • Notice now in R3 there is a OSPF learned E2 default gateway
  • Of course, there are options with default-information originate 
    • always - meaning originate a default even if there isn't one installed in the routing table 
    • metric - set the metric of the route being originated
    • metric type - set the metric type of default route to be either E1 or E2 
    • route-map - of course, manipulate the advertisement to your heart's content. 

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