How to configure OSPF with BGP on top

Configuring OSPF (Open Shortest Path First) with BGP (Border Gateway Protocol) on top is a common practice in large-scale networks where OSPF is used for intra-domain routing and BGP is used for inter-domain routing. This approach is often referred to as “OSPF as the IGP (Interior Gateway Protocol) and BGP as the EGP (Exterior Gateway Protocol).” Here’s a basic guide on how you can configure OSPF and BGP coexistence:

OSPF Configuration:

Assuming you have your OSPF network configured, you can do the following:

1. Access Global Configuration Mode: Enter global configuration mode on the router:
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   router# configure terminal

2. Configure OSPF: Enable OSPF and configure OSPF parameters:
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   router(config)# router ospf <process-id>
router(config-router)# network <network-address> <wildcard-mask> area <area-id>


   Repeat this step on all routers participating in OSPF.

3. Configure OSPF Redistribution (If Needed): If you have other routing protocols or static routes, you may need to redistribute them into OSPF:
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   router(config)# router ospf <process-id>
router(config-router)# redistribute <source-protocol> <source-id> metric <metric>


BGP Configuration:

1. Access Global Configuration Mode: Enter global configuration mode on the router:
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   router# configure terminal

2. Configure BGP: Enable BGP and configure BGP parameters:
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   router(config)# router bgp <your-AS-number>
router(config-router)# neighbor <neighbor-IP-address> remote-as <neighbor-AS-number>


   Repeat this step on all routers participating in BGP.

3. Configure BGP Network Statements: Advertise BGP network prefixes:
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   router(config-router)# network <network-address> mask <subnet-mask>

4. Configure BGP Redistribution (If Needed): If you have OSPF routes or other routes you want to advertise via BGP, redistribute them into BGP:
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   router(config-router)# redistribute ospf <process-id> subnets


Verification and Monitoring:

• Verify OSPF Configuration:
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  router# show ip ospf neighbor
router# show ip route ospf

• Verify BGP Configuration:
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  router# show ip bgp summary
router# show ip bgp

• Check BGP Routes:
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  router# show ip route bgp

• Check BGP Neighbors:
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  router# show ip bgp neighbors


Save Configuration:

Save your configurations to ensure they persist after a reboot:

Remember that this is a basic example, and the exact commands may vary based on your network topology and requirements. Ensure that your OSPF and BGP configurations are consistent across all routers in your network. Always refer to the documentation for your specific router platform and software version for the most accurate information.