In this case, two devices that function as ASBR should be configured to generate the redistribution of the default route in the ASBR, this will allow the necessary redundancy to be had so that when one of these ASBR does not work, the traffic can pass through the ASBR. second ASBR that generated the default route redistributions.

Having two routers configured as ASBRs (Autonomous System Boundary Routers) allows for more effective routing management and provides high availability for Internet connections. Let's see how to implement it step by step:

Configuring ASBRs for Default Route Redistribution

1. ASBR Selection: Choose two routers in strategic locations, preferably at the ends where Internet accesses connect, to act as ASBRs. These routers will be responsible for redistributing the default routes within the OSPF domain.
2. Default Route Redistribution:
   • On each ASBR, first make sure you have a static default route configured to its respective Internet access.
   • Then, in the OSPF configuration of each ASBR, enable redistribution of this route by default in OSPF. This can be done through the command line interface or graphical configuration tools, specifically indicating that you want to redistribute the default routes.
3. Cost Adjustments (Optional): To manage how one default route is preferred over another (for example, whether one of the Internet accesses should be preferred over the other under normal conditions), you can adjust the cost of the redistributed route in each ASBR. This will affect the routing decision within OSPF to select the primary and secondary default route.

Guaranteeing Redundancy

• Monitoring and Automatic Failover: OSPF will automatically adjust routes within the network if one of the ASBRs stops advertising its default route, for example, due to a failure in the Internet access it is connected to. This provides an automatic failover mechanism so that traffic can be rerouted through the other ASBR without manual intervention.
• Load Balancing Considerations: If both Internet accesses are active and you want to load balance between them, be sure to correctly configure costs on the redistributed paths and consider using ECMP (Equal-Cost Multi-Path) to allow OSPF to send traffic through both ASBRs equitably.

Testing and Validation

• Test to ensure that default route redistribution is working as expected. You can do this by checking the routing tables on the other OSPF routers to see if they are learning the default route over OSPF.
• Test failure scenarios by manually disconnecting one of the Internet accesses to verify that traffic is automatically rerouted through the other ASBR.

Configuring two ASBRs for default route redistribution in an OSPF network provides a robust redundancy solution, ensuring that the network can continue to operate efficiently even if one of the Internet accesses fails.

This configuration improves network resiliency and availability, critical elements for any modern network infrastructure.