Looking for OSPF job? Dont know how to win interview? Here's how. Search and apply for OSPF jobs on wisdom jobs with immediate effect. OSPF is abbreviated as Open Shortest Path First and is routing protocol for IP networks. It is important to get the knowledge on OSPF to get the job in the big companies with ease. Wisdomjobs.com brings you a big list of ospf job interview questions and answers related to OSPF to make your efforts of getting a job in the field easy. These job interview questions and answers are framed by the experts in the field so, you can find most of the questions asked during the interview. Check out for the career solutions on wisdom jobs.
Open shortest path first is an Open Standard Link State routing protocol which works by using Dijkastra algorithm to initially construct the shortest paths and follows that by populating the routing table with resulting best paths.
we would divide the autonomous system into various areas to keep route updates to a minimum to conserve resources and to keep problems from propagating throughout the network.
The following are benefits of dividing the entire network into areas -
While configuring multi-area OSPF, one area must be called area 0, referred to as backbone area. All other areas must connect to backbone area as inter-area traffic is send through the backbone area.
It is the router that connects other areas to the backbone area within an autonomous system. ABR can have its interfaces in more than one area.
It is the Router that connects different Autonomous Systems.
Router Id is used to identify the Router. Highest IP address of the router's loopback interfaces is chosen as the Router ID, If no loopback is present than highest IP address of the router's physical interfaces will be chosen as Router ID.
The following parameters must be the same on both routers in order for routers to become neighbors:-
Command to change the priority on an interface
router(config)# interface fa0/0
router(config-if)# ip ospf priority 100
All OSPF routers will form adjacencies with the DR and BDR. If link-state changes, the update will be sent only to the DR, which then forwards it to all other routers. This greatly reduces the flooding of LSAs therefore conserving the bandwidth.
OSPF routers need to go through several states before establishing a neighbor relationship:-
1.Down - No Hello packets have been received on the interface.
2.Attempt - In Attempt state neighbors must be configured manually. It applies only to nonbroadcast multi-access (NBMA) networks.
3.Init state - Router has received a Hello message from the other OSFP router.
4.2way state - The neighbor has received the Hello message and replied with a Hello message of his own. Bidirectional Communication has been established. In Broadcast network DR-BDR election can occur after this point.
5.Exstart state – DR & BDR establish adjacencies with each router in the network. Master-slave election will takes place (Master will send its DBD first).
6.Exchange state – Routing information is exchanged using DBD (Database Descriptor) packets, Link-State Request (LSR). Link-State Update packets may also be sent.
7.Loading state – LSRs (Link State Requests) are send to neighbors for every network it doesn't know about. The Neighbor replies with the LSUs (Link State Updates) which contain information about requested networks. The requested information have been received, other neighbor goes through the same process
8.Full state - All neighbor routers have the synchronized database and adjacencies has been established.
The LSAs (Link-State Advertisements) are used by OSPF routers to exchange routing and topology information. When two neighbors decide to exchange routes, they send each other a list of all LSA in their respective topology database. Each router then checks its topology database and sends Link State Request (LSR) message requesting all LSAs that was not found in its topology table. Other router responds with the Link State Update (LSU) that contains all LSAs requested by the neighbor.
Hello interval - This defines how often OSPF router will send the hello packet to other OSPF router.
Dead interval - This defines how long a router will wait for hello packets before it declares the neighbor dead.
The default Hello Interval for OSPF is 10 seconds.
The Dead Interval is four times the Hello Interval. By default it is 40 seconds.
OSPF use the multicast address of 22.214.171.124 & 126.96.36.199.
Router participating in OSPF routing protocol maintains three OSPF tables:-
1.Neighbor table - Stores information about OSPF neighbors.
command to see # sh ip ospf neighbor
2.Topology table - Stores the topology structure of a network.
command to see # sh ip ospf topology
3.Routing table - Stores the best routes to all known networks.
command to see # sh ip route ospf
router(config)# router ospf 10
router(config-router)# network 188.8.131.52 0.0.0.255 area 0
router(config-router)# network 184.108.40.206 0.0.255.255 area 1
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