OPSF:
-Open Shortest Path First (OSPF) is a widely used interior gateway protocol for IP networks.
-It is a link state routing protocol that calculates the shortest path to a destination using the Dijkstra algorithm.
-Open Standard.
- AD value 110
Key features of OSPF include:
Hierarchical design: OSPF divides the network into smaller sub-networks called areas, reducing the amount of routing information exchanged between routers.
Fast convergence: OSPF is known for its fast convergence time, ensuring the network continues to operate smoothly in the event of a failure.
Equal-cost multi-path routing: OSPF supports equal-cost multi-path routing, allowing multiple paths to a destination to be used simultaneously.
Authentication and encryption: OSPF provides support for authentication and encryption to secure the exchange of routing information.
Widely used: OSPF is widely used in real-world networks, including service provider networks, enterprise networks, and data center networks.
VLSM Support: Carries Subnet Mask information in routing update.
Open Standard -Multivendor
Support.
Independent Transport – Use IP protocol 89 not TCP/UDP.
Neighborship Criterion:
Router ID: The Router ID is a unique identifier for each OSPF router,
Area ID: The Area ID must match between the two routers in order for them to form a neighbor relationship.
Hello and Dead Intervals: The Hello interval and Dead interval must match between the two routers in order for them to form a neighbor relationship.
Authentication: If authentication is enabled, the authentication type and key must match between the two routers in order for them to form a neighbor relationship.
Subnet Mask: The subnet mask must match between the two routers in order for them to form a neighbor relationship. Routers on different subnets do not form neighbor relationships.
MTU (Maximum Transmission Unit): In OSPF, the MTU size must match between two routers in order for them to form a neighbor relationship. If the MTU size is different between two routers, this can cause issues with communication and packet loss.
Stub Area Flag:
A Stub Area is a type of OSPF area that does not receive information about routes from other areas and only receives default routes.
The Stub Area Flag is used to indicate that a router is part of a stub area, and must match between two routers in order for them to form a neighbor relationship.
If the Stub Area Flag is set differently between two routers, this can cause issues with routing and communication.
OSPF States:
States are important for understanding the behavior of OSPF and for troubleshooting OSPF-related issues.
The states of OSPF are:
Down: The OSPF process has not been enabled on the router, or there is a problem with the configuration or network connectivity that prevents OSPF from starting.
Attempt: The OSPF process has been enabled, but the router has not yet established communication with its neighbors.
Init: The router has discovered its OSPF neighbors and is in the process of exchanging information with them to build a complete view of the network topology.
Two-Way: The router has established communication with its neighbors and has received information about the network topology. The router is now able to send and receive routing updates.
ExStart: The router has started the process of electing a designated router (DR) and a backup designated router (BDR) to manage communication between routers on a network segment.
Exchange: The router is exchanging database information with its neighbors to build a complete view of the network topology.
Loading: The router has received a complete view of the network topology and is in the process of calculating the shortest path to each destination.
Full: The router has completed the calculation of the shortest path to each destination and is now sending and receiving routing updates. The router is fully operational and can participate in the routing process.