Updated April 4, 2023
Definition of OSPF Interview Questions
OSPF is a consistent link and abbreviated as OPEN SHORTEST PATH FIRST method belongs to internet protocol routing techniques which are effectively applicable in larger networks. It is the interior gateway for the internet which distributes the details of IP using a unit autonomous system. The routers of OSPF transfers the information, routing path, and cost to the adjacent OSPF neighbors. It follows the Dijkstra algorithm to find the shortest available path and this computing process depends on the cost. OSPF doesn’t have any hop-count limit.
OSPF Interview Questions with Answers
Let us discuss the interview questions of OSPF.
1. What is the function of OSPF?
It examines the area and establishes a relationship with the neighbor router in that area. It implies a link state advertisement policy to pass the status of directly connected links within the network. It gets refreshed 30minutes and checks if there is any change in the routing process. It uses Dijkstra’s algorithm to find the minimum path and transfers the information in the network.
2. How many routing tables are formed and what is the topology behind them?
The neighbor table comprises adjacent routers, the routing table holds the best routes, and the topology table includes all the possible routes in that area. The possible topology is 2-way, Exchange. Full, Advertisement, Loading, and Down.
3. If the priority of OSPF is changed to zero, what will be the result?
Once it is changed to zero, it doesn’t involve in BDR or DR election
4. Explain the packets in OSPF?
• The packets are LSR, LSU, LSA, Hello, and Dead timers.
• LSA holds details or updates the network
• LSU comprises of recent updates.
• Hello is a verification packet that ensures the alive state across the OSPF interface.
• Dead is the state where there is no connection established from the router and it will remove that router from the table.
• LSR is like a request packet that updates the working OSPF to perform in an updated way.
5. Is there any election happen in point to point network?
No DR or BDR election takes place in point to point network.
6. Is it possible to exchange area 1 and area 2, if it is not linked to area 0?
Area 0 is called a backbone area and all the areas should be connected to it to exchange the internal area routes and there is no possible way of establishing a virtual link.
7. Define OSPF’s virtual link?
According to the OSPF method, the internal area communication will occur only if one area and the backbone area stay connected. A virtual link is employed to develop a logical association when the OSPF method is failed.
8. Explain the election scenario of BDR or DR in OSPF?
DR election happens to evade full mesh scenarios and works in a shared multi-access network. In a shared network, the OSPF router tries to connect with the neighbor and here DR or BDR acts as SPOC to connect only that two routers. The highest priority is made from the DR router and the next priority will be decided from the BDR router. If there is any same decision, then the process continues on the decision of the highest router-id. It is chosen as the maximum active IP which generates the first possible route value. It is used to solve the maximum number of adjacencies and over flooding of LSA.
9. List out the different types of LSA?
In type 1- (router LSA), all the OSPF router communicates with LSA
In type 2 (network LSA), it is employed in DR or BDR election across a multi-access network.
In type 3 (summary LSA), LSA helps area border router to exchange the inter-area data.
In type 4 (summary ASBR LSA), external communication takes place with different protocol and collect the position information of ASBR.
In type 5 (external LSA), is produced by ASBR and shares the details of external routes.
Type 7 (not so stubby) is employed in a special area and gets changed to type 5 by the area border router
10. Explain the different types of OSPF networks?
Broad multi-access networks represent topology where broadcast establishes.
Point to point network is established when two routers are connected directly
Point to the multipoint network occurs when one interface is connected to many destinations.
Non-broadcast multiple access network, here no broadcast is possible but one router is connected to many routers.
11. How to change the adjacency of neighbors?
By using state request LSR packets, then establish link state and inform using LSU packets.
Then it creates dual-way confirmation, after that database synchronization occurs, the two routers are considered as adjacent.
12. Explain different areas in OSPF
OSPF is built as a structural hierarchy and by using the area it manages and controls the database traffic. It creates stability and avoids unwanted converging updates across the network. The backbone area is logically and physically connected with other areas for communication. Information sent by ABR cannot be shared across two areas. The stub area stops the external details sent by ABR and blocks LSA 5 and LSA 4 to reduce traffic flow. As an alternate method, the connection is established by using the default route table configured by ABR. So if any router wants to connect in the stub area, it follows the default route table. A total stub area is similar to a stub area and it stops LSA 5,4 and LSA 3 and ABR defines the default routing table for communication.
13. What are the possible issues if neighborship of OSPF in the downstate?
The IP and mask of the connecting devices should be correct and the cables connected across should be in back to back method. Execute the OSPF process and if it is not running then advertise the details to both routers. Dead timer and Hello timer should be the same at both terminals. There should not be any blocking of a transparent firewall of IP addresses. Then check for the establishment of neighborship. Both authentication parameters and area numbers should be matched. If the issue exists, check for router logs and analyze the problem.
The above-mentioned points are few basic queries of OSPF. OSPF being a huge area of study, there can be a variety of topics that can be interviewed on it. The points above can consolidate the most mandatory and crucial questions that can be asked.
This is a guide to OSPF Interview Questions. Here we discuss the definition, list of OSPF Interview Questions for better understanding. You may also have a look at the following articles to learn more –