TOP 10 OSPF INTERVIEW QUESTIONS AND ANSWERS

Question 1 –Tell us something about OSPF ?

ANSWER

Open Shortest Path First (OSPF) is an IGP Routing Protocol
It is a Open standard Routing Protocol i.e can be used on multivendor devices.
Link State Routing Protocol.
OSPF routers have End –to- End Visibility of entire network in form on Topology table.
Uses Dijkstra  SPF  (Shortest Path First) Algorithm to find best route from source to destination.
AD =110.

Question 2 –What is the metric in OSPF?

ANSWER

Metric is Cost.
Cost depends upon Bandwidth of the link .
Cost is Inversely proportional to the Bandwidth.
Means Greater the Bandwidth less the cost and better the path.
Cost = 100 / Bandwidth (in Mbps)

Question 3 –What is OSPF Router ID?

ANSWER

Identification of OSPF Router in the OSPF Domain.
It is the highest IP Address of Loopback interfaces and in absence of loopback it is the Highest IP of the active physical interface.
We can also set it  manually but it will take effect when OSPF process is reset completely or device is reloaded.

Question 4 –What are the tables which are built and maintained in OSPF ?

ANSWER

Neighbor table – contains a list of all OSFP Neighbors.
Topology table – contains a list of all possible routes to reach all networks within an area.
Routing table – contains the best route for each known network.

Question 5 –What is the concept of “Area” in OSPF?

ANSWER

In OSPF each Router have visibility of the entire network in form on Topology table .
Each router sends SPF update to each other.
So whenever we are running OSPF on huge network where the hundreds of Routers are present and each router is handling thousands of routes.
Means each router in OSPF domain will be busy in processing Frequent SPF updates (which depends on the size of the OSPF Domain)
So to control Frequent SPF updates in OSPF domain -Areas are created which contains certain OSPF routers and  will  localize the routing updates with in a single Area.

Question 6 –Timers in OSPF ??

ANSWER

The timers depends upon the network type.
By Default Timers –
Broadcast network which include Ethernet, point-to-point and point-to-multipoint are 10 seconds hello and 40 seconds dead.
Non-broadcast network are 30 seconds hello 120 seconds dead.

Question 7 –What is the criteria to form OSPF Neighborship  ??

ANSWER

Should Match below parameters
A N T P
Area ID
Network Mask
Timers – Hello & Dead
Authentication Password.

Question 8 –What are external routes in OSPF ??

ANSWER

Whenever routes are redistributed from different routing protocol or from different OSPF process in to OSPF ; these routes are known as External routes.
These routes are propagated as LSA 5 in OSPF   Domain.

Question 9 –What is STUB Area in OSPF & what is the advantage ??

ANSWER

Stub Area will be a area with single exit point.
Stub Area –A area in which external routes LSA 5 will not propagate.
But instead ABR will generate a default router on all internal routers of stub area pointing towards ABR. (for connectivity)

Question 10 –What is DR & BDR in OSPF?

ANSWER

In OSPF on Multiaccess network DR & BDR are elected to eliminate a huge amount of traffic and chaos in the network.
DR is the router with Highest OSPF Priority (default is 1).If all the routers have same priority then election goes on RID ; router with highest RID will become DR.

Thanks for Reading !!!!!!