OSPF (Open Shortest Path First) is a widely-used link-state routing protocol. Nowadays, a career in networking can be quite lucrative, and its opportunities are increasing rapidly. If you plan to apply for an OSPF post, then there are a set of OSPF interview questions you must be prepared for. This article acquaints you with top OSPF interview questions covering different areas. Take a look!
Do not worry! You can totally rely on us if you want to practice OSPF Interview Questions. We have researched, picked up, and listed some OSPF interview questions that are most frequently asked.
It has become increasingly important to protect our data in this fast-changing technological era. Indeed our life has become easier due to the digital revolution. But the world is becoming more complex due to this technological advancement. The network is a crucial element for using technology. And we can access that with the help of a router. But the process is not that simple. It involves Internet protocol. OSPF is one such routing Internet protocol that takes care of the algorithm from source to destination. It is a task for experts, and thus, the demand for OSPF professionals is constantly growing.
We will move to OSPF Interview Questions- 2022 (Updated) for the following:
Top OSPF Interview Questions:
If you are new to the world of OSPF, here are some fundamental questions to prepare for your interview.
OSPF utilizes the Dijkstra Shortest Pathway First algorithm to decide the shortest and the most suitable path. It shows the status of straight related links using LSA- Link State Advertisements. It also notifies in case of any updates or changes in any of the links. Link State Advertisements are refreshed every 30 minutes.
Type-3 Link State Advertisement is used for communication amongst the regions. Type 4 and Type 5 Link State Advertisements are for communicating within other external protocols.
Different types of LSA used in OSPF are given below:
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There are five types of OSPF packets. These are:
Different types of OSPF are:
There are two types of intervals in OSPF. These are:
OSPF uses two multicast address- 126.96.36.199 and 188.8.131.52
OSPF router ID works as an identifier. It is used to recognize the router. It is a 32-bit number.
The 11.2 Cisco IOs Software Release allows the change of Bandwidth. You can change it with the help of the OSPF auto-cost-reference bandwidth command under “router OSPF.” The default bandwidth is 100 Mbps. And the OSPF link cost is a 16-bit number. Thus, the maximum value for this change is 65,535.
Yes, the OSPF routing protocol exchanges are authenticated. OSPF can authenticate all the packets to be exchanged between the neighbor routers. This authentication can occur through easy passwords. For configuring the authentication, you can use the command IP OSPF authentication key.
This will assign an eight-octet password to the interface attached to each area. However, if you want to configure the authentication on some interfaces, you can go for alternate methods or different interfaces belonging to the same area.
An OSPF adjacency is a theoretical link for a neighbor over which we can send the Link State Advertisements (LSAs).
Following are the steps to change neighboring ships into adjacency:
In OSPF, LSA means Link State Advertisement. While LSU is Link State Update, LSR stands for Link State Request.
In DR/BDR, it uses 184.108.40.206 and 220.127.116.11.
Different router types can be described as follows:
If you are up skilling yourself in the OSPF field and looking for advance level questions to prepare for, you can take help from the below list.
The distribute-list commands are supported in OSPF but only in some conditions. It is also different from a distance vector routing protocol like Routing Information Protocol and Enhanced Interior Gateway Routing Protocol (EIGRP). And it is noteworthy that OSPF routes cannot be filtered while entering the OSPF database. The distribute-list in command only filters from entering the route. It doesn’t prevent the propagation of link-state packets. Thus, the route memory is not conserved in this process. Also, this propagation might affect other routers as well.
Also, it would help if you were careful as the distribution list in command needs to be implemented carefully. If not, there are chances that loops will occur. This command only works on the routes of Autonomous System boundary Routers.
OSPF is required to send an acknowledgment of every new link state advertisement. This is done by sending LS packets. These packets keep on transiting until they are acknowledged. Retransmissions are defined by this Link State Retransmit Interval. The command for this IP OSPF retransmits interval. The value is 5 seconds by default.
IP-OSPF-Transmit-Delay is used to add a specified time to the age field of an update. It needs to be added before the transmission over a link. If not, then the time in which LSA propagates won’t be considered. The value is 1 second by default. This is more significant on low-speed links for certain reasons.
Not really. OSPF can only generate a default when it is configured using the command default-information originate. It also works if there is already a default network in the box from a different process. Remember that the default route is 0.0.0.0. If an OSPF-enabled router does not have a default router and you want to generate it, use the command “default-information originate.”
Apart from using the normal commands for OSPF configuration, we require some special commands for running it in the Primary Rate Interface and the Basic Rate Interface. When you use the normal OSPF configuration commands, you should use the dialer map command. Also, broadcast keywords are essential here to indicate that the broadcasts need to be forwarded.
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We require special commands to run OSPF on links that do not occur at a certain predetermined time. For this, we can use the async default routing command on the asynchronous interfaces. This enables the router to continue passing updates to other routers with the same interfaces.
Area 0 is known as the backbone area in OSPF. In simple language, all other areas send their transfer through this area only. It cannot function without this. The entire routing area is also distributed through this.
Four types of areas in OSPF are given below:
OSPF maintains the below three tables:
The benefits of OSP summarization are:
The different network types in OSPF are listed below:
The functions of the neighbor router are given below:
According to the OSPF rule, inter-area communication happens when at least one area is 0 or the backbone area. A virtual link has to be used to form a logical association in case it’s not possible. And a virtual link is not feasible via the stub area.
In OSPF, DR means Designated Router, and BDR means Backup Designated Router. Both of them are used for exchanging information between different routers. DR is the contact point for the network segment by default. BDR is selected for the network to avoid problems with DR whenever these occur.
E1 is an External Type route that defines the cost that is required to the destination from ASBR (Autonomous System Boundary Router). Here, the internal cost and the external metric are considered.
E2 is also the External Type route, but it doesn’t include the internal costs. In E2, it calculates only the external metrics for reaching a particular destination.
The full form of OSPF is Open Shortest Path First. It is a routing Internet protocol. It is the open link and works by utilizing Dijkstra’s SPF algorithm to find straight paths from your source to your destination. It is an intra-domain protocol. This means that it is used within a particular area of a network. It is designed only for a single autonomous system.
The work of a router is to learn routes. OSPF does the same. It learns about each router within the entire network. The link-state routing algorithm present in it gives out the information of every domain. OSPF learns the information by sending Link State Advertisements.
The steps are given below:
Following are the critical attributes of OSPF:
The characteristics of OSPF are given below:
BDR and DR are important because they solve the following two problems in OSPF:
Yes. It is possible to have OSPF over a GRE tunnel.
OSPF summarization, also known as Route summarization, helps in reducing OSPF traffic and computation. This results in preventing the memory from getting wasted.
To make two routers neighbors, the following parameters should match:
OSPF goes through the below seven stages:
These were some of the OSPF Interview Questions that could be asked in your next interview. Remember that it is an essential part of every dimension of life, especially work. And it opens the doors of opportunities in many ways. You cannot miss a chance to grab them, and this article will make you even well-versed with the knowledge. Keep practicing, and good luck!
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Kalla Saikumar is a technology expert and is currently working as a content associate at MindMajix. Write articles on multiple platforms such as ServiceNow, Business Analysis, Performance Testing, Mulesoft, Oracle Exadata, Azure, and other courses. And you can join him on LinkedIn.
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