OSPF Protocol Cheatsheet – Basic Functionality

  1. OSPF Overview:
    • OSPF (Open Shortest Path First) is an Interior Gateway Protocol (IGP) used for dynamic routing in IP networks.
    • OSPF operates on the concept of areas, which helps in scaling large networks and reducing routing overhead.
    • OSPF uses Link State Advertisements (LSAs) to exchange routing information and build a database of network topology.
  2. OSPF Areas:
    • Area 0 (Backbone Area): Central area that connects all other OSPF areas.
    • Non-Backbone Areas: Additional areas connected to the backbone area.
    • Area ID: Unique identifier for each OSPF area.
  3. OSPF Message Types:
    • Hello: Used to discover and maintain neighbor adjacencies. Sent periodically to establish and verify neighbor relationships.
    • Database Description (DBD): Exchanges information about LSAs between routers during initial adjacency formation.
    • Link State Request (LSR): Requests specific LSAs from a neighboring router.
    • Link State Update (LSU): Carries LSAs in response to LSRs or when network changes occur.
    • Link State Acknowledgment (LSAck): Acknowledges the receipt of LSU packets.
  4. OSPF Configuration Commands:
    • Enter OSPF configuration mode:
      configure terminal
      router ospf <process-id>
    • Assign OSPF process ID:
      router ospf <process-id>
    • Configure OSPF on interfaces:
      interface <interface>
      ip ospf <process-id> area <area-id>
    • Set OSPF network type:
      interface <interface>
      ip ospf network <type>
    • Set OSPF router ID:
      router-id <router-id>
    • Advertise OSPF networks:
      network <network> <wildcard-mask> area <area-id>
    • Set OSPF authentication:
      interface <interface>
      ip ospf authentication <type>
  5. OSPF Verification Commands:
    • Verify OSPF neighbors:
      show ip ospf neighbor
    • View OSPF database:
      show ip ospf database
    • Check OSPF routing table:
      show ip route ospf
    • Display OSPF interface information:
      show ip ospf interface
    • Show OSPF summary information:
      show ip ospf summary
  6. OSPF Troubleshooting:
    • Verify OSPF configuration on routers.
    • Check OSPF neighbor adjacencies.
    • Ensure OSPF network types are correctly configured.
    • Verify OSPF area assignments.
    • Confirm OSPF router IDs are unique.
    • Check OSPF authentication settings.
    • Validate OSPF LSDB synchronization between routers.

This OSPF protocol cheatsheet provides an overview of the basic functionality, including areas and message types. It also includes important configuration and verification commands to help you understand and work with OSPF in your network environment. Refer to official documentation and additional resources for more in-depth information on OSPF protocol and its advanced features.