Top 100+ Ospf Interview Questions And Answers
Question 1. What Is Ospf Routing Protocol?
Open shortest course first is an Open Standard Link State routing protocol which goes through the use of Dijkastra set of rules to initially construct the shortest paths and follows that by means of populating the routing desk with ensuing excellent paths.
Question 2. Mention Some Characteristics Of Ospf?
OSPF is a classless routing protocol that helps VLSM and CIDR.
It permits for creation of areas and self sustaining device.
OSPF makes use of cost as its metric, that's computed based totally on the bandwidth of the hyperlink.
It has no hop-remember limit. It supports limitless Hop count number.
OSPF helps both IPV4 & IPV6.
OSPF routes have an administrative distance of 110.
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Question three. What Is The Need For Dividing The Autonomous System Into Various Areas?
we might divide the self sustaining system into various regions to hold path updates to a minimum to conserve assets and to keep troubles from propagating at some point of the network.
Question four. What Is The Benefit Of Dividing The Entire Network Into Areas?
The following are advantages of dividing the whole community into regions -
Decrease routing overhead.
Speed up convergence.
Confine network instability to unmarried areas of the network.
Question five. What Is Backbone Area?
While configuring multi-region OSPF, one region need to be known as location 0, called spine location. All different regions must hook up with spine vicinity as inter-vicinity traffic is ship thru the spine region.
Switching Interview Questions
Question 6. Explain Area Border Router(abr)?
It is the router that connects different areas to the backbone location inside an independent system. ABR can have its interfaces in more than one region.
Question 7. What Is Autonomous System Border Router (asbr)?
It is the Router that connects one of a kind Autonomous Systems.
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Question eight. What Is Ospf Router Id?
Router Id is used to discover the Router. Highest IP cope with of the router's loopback interfaces is selected as the Router ID, If no loopback is present than highest IP cope with of the router's bodily interfaces can be chosen as Router ID.
Question nine. What Parameters Must Match For Two Routers To Become Neighbors?
The following parameters need to be the identical on both routers so as for routers to end up neighbors:-
Hello and Dead interval time
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Question 10. How Ospf Dr & Bdr Is Elected?
The router with the very best precedence will become the DR and router with 2d maximum priority becomes the BDR. If there's a tie in precedence, router with the very best Router ID will become DR.
By default precedence on Cisco routers is 1. We can manually change it.
If the Router precedence is about to zero (Zero), that router will not take part in DR/BDR election.
DR election technique is not preemptive. If a router with a better priority is introduced to the network, it's going to now not become DR untill we clear OSPF manner and DR/BDR election takes place again.
Command to change the concern on an interface
router(config)# interface fa0/zero
router(config-if)# ip ospf priority 100
Question eleven. Why Dr And Bdr Are Elected In Ospf?
All OSPF routers will shape adjacencies with the DR and BDR. If hyperlink-nation changes, the replace may be sent most effective to the DR, which then forwards it to all different routers. This greatly reduces the flooding of LSAs consequently maintaining the bandwidth.
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Question 12. Explain The Various Ospf States?
OSPF routers want to undergo numerous states before organising a neighbor courting:-
1.Down - No Hello packets had been received at the interface.
2.Attempt - In Attempt nation pals must be configured manually. It applies handiest to nonbroadcast multi-get admission to (NBMA) networks.
3.Init kingdom - Router has received a Hello message from the opposite OSFP router.
Four.2way country - The neighbor has received the Hello message and answered with a Hello message of his personal. Bidirectional Communication has been established. In Broadcast community DR-BDR election can arise after this point.
5.Exstart state – DR & BDR set up adjacencies with every router in the network. Master-slave election will takes region (Master will ship its DBD first).
6.Exchange nation – Routing statistics is exchanged using DBD (Database Descriptor) packets, Link-State Request (LSR). Link-State Update packets may also be sent.
7.Loading kingdom – LSRs (Link State Requests) are send to acquaintances for each community it doesn't understand approximately. The Neighbor replies with the LSUs (Link State Updates) which contain statistics approximately requested networks. The requested data had been received, other neighbor goes via the equal technique
eight.Full kingdom - All neighbor routers have the synchronized database and adjacencies has been hooked up.
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Question 13. Explain Ospf Lsa, Lsu And Lsr?
The LSAs (Link-State Advertisements) are used by OSPF routers to trade routing and topology data. When two pals decide to change routes, they ship every other a listing of all LSA of their respective topology database. Each router then assessments its topology database and sends Link State Request (LSR) message requesting all LSAs that turned into not observed in its topology desk. Other router responds with the Link State Update (LSU) that includes all LSAs requested with the aid of the neighbor.
Question 14. What Are The Steps Required To Change Neighborship Into Adjacency?
Two-manner verbal exchange (the use of Hello Protocol)
Database Synchronization which means that change of Database Description (DD) packets, Link State Request (LSR) packets, Link State Update (LSU) packets.
After Database synchronization is entire, the two routers are considered adjacent.
Question 15. Explain Ospf Timers?
Hello c language - This defines how frequently OSPF router will ship the hello packet to different OSPF router.
Dead interval - This defines how long a router will look ahead to hello packets earlier than it pronounces the neighbor dead.
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Question sixteen. What Is The Default Hello Interval?
The default Hello Interval for OSPF is 10 seconds.
Question 17. What Is The Default Dead Interval?
The Dead Interval is four instances the Hello Interval. By default it is 40 seconds.
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Question 18. What Multicast Address Does Ospf Use?
OSPF use the multicast address of 224.Zero.0.Five & 220.127.116.11.
Switching Interview Questions
Question 19. Tables Maintained By Ospf?
Router taking part in OSPF routing protocol keeps 3 OSPF tables:-
1.Neighbor table - Stores information about OSPF friends.
Command to see # sh ip ospf neighbor
2.Topology table - Stores the topology structure of a community.
Command to peer # sh ip ospf topology
3.Routing desk - Stores the great routes to all known networks.
Command to look # sh ip course ospf
Question 20. What Are Different Ospf Lsa Types ?
Router LSA (Type1) - Each router generates a Type 1 LSA that lists its lively interfaces, IP addresses, buddies and the cost. LSA Type 1 is flooded simplest within a place.
Network LSA (Type2) - Type 2 LSA is despatched out with the aid of the specific router (DR) and lists all of the routers at the segment it's miles adjoining to. Type 2 LSA are ?ooded simplest within a place. It incorporates the facts about DR's.
Summary LSA (Type3) - Type three LSAs are generated by means of Area Border Routers (ABRs) to advertise networks from one region to the rest of the areas in Autonomous System. It contains the records approximately inter-place routes.
Summary ASBR LSA (Type4) - It is generated via the ABR and incorporate routes to ASBRs.
External LSA (Type5) - External LSAs are generated through ASBRs and comprise routes to networks which are external to current AS.
Not-So-Stubby Area LSA (Type7) - Stub areas do now not permit Type 5 LSAs. A Not So Stubby Area (NSSA) lets in commercial of Type five LSA as Type 7 LSAs. Type LSA is generated by way of an ASBR internal a Not So Stubby Area (NSSA) to describe routes redistributed into the NSSA.
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Question 21. How Do We Configure Ospf Routing Protocol?
router(config)# router ospf 10
router(config-router)# community 18.104.22.168 0.0.0.255 area zero
router(config-router)# network 23.1.0.Zero zero.Zero.255.255 place 1
router(config-router)# go out
Router ospf 10 command enables the OSPF system. Here “10” shows the OSPF procedure ID and can be unique on neighbor routers. Process ID lets in more than one OSPF tactics to run at the identical router.
Second command configures 12.1.1.Zero/24 community in location zero.
Third command configures 23.1.0.Zero/16 network in location 1.