hi guys this is Amar and welcome to network engineer stuff so guys in this video we're going to focus on top 20 CCNA level interview question and answers so let's start with question number one so question number one says that tell us something about OSI model so guys who are fresher or guys mostly fresher guys they will definitely face this into question that what is OSI model now this OSI model is nothing but uh a reference model always remember this word reference this OSI model is a reference model and this have seven layer in this model so it's a seven layer architecture and uh this OSI it stands for basically open system inter connection also mention this point and you may or may not Point mention this second point that is it has been developed by ISO in year 1984 but you do have to mention that OSI model is a reference model and it's a seven layer architecture so when we say seven layer architecture the immediate question would come what are the seven layers in the OSI model so layers in OSI model are layer one is physical layer Layer Two is data link layer Layer Three is Network layer layer four is transport layer layer five is session layer layer six is presentation layer and layer seven is application layer so you have to remember this particular layers in this order and this all these layers have uh specific uh functionality so you can can go and study uh if you if you want that notes I can provide you I can write in the uh description section I'll give you or in the comment section of this video I'll again give in the description section of video also the link of each and every uh layer uh functionality so you have to me mention or you have to remember this in an particular order when you are uh answering this question so the way I remembered was using the statement that is please do not tell sales people anything so p is physical D is data link n is Network t transport s is session P again this is presentation and a is application so you can remember in in the way you want to remember but you have to remember so let's move on to question number three what is a IP address so IP address is is basically address address of a device so this is an an identity of an that particular device this identity is required for communication it simple as as you have your address your your resident address and it is required for the for some communication right if somebody wants to communicate you via some uh some letter it will it will require your address so in the same way an IP address is required for IP communication and this IP address is given to a device now this IP address uh is can be 32bit or 128bit address uh depending upon the version now IP address have two versions that is IP V4 and IP V6 so if it is an IP V4 we see IP V4 address means it's a 32bit address and if we say it's an IPv6 address that means it's in 128 bits address so you can see over here that uh this particular address that is 19210 8.0.1 now this is ipv4 address it's in 32bit address let's move to question number four what is the difference between a hub switch and a router uh this is a very commonly asked question and the best way to answer this question is always remember that this Hub is uh a layer one device switch is Layer Two and router is layer three uh Hub is a dump device we can see it's a dump device it basically only connects multiple devices in your land and it operates at layer one so when we say it's a layer one device means it operates at layer one physical layer when we say switch is uh switch is a bit intelligent device as compared to the hub so when we say switch is a layer to device means it operates at Layer Two means it uses Layer Two addresses for communication that is Mac addresses so switches uses Mac address for communication and routers are operates at layer three and uh they uses layer three addresses that is IP addresses for making their for decision so they basically uh routers are used to connect different networks so whenever you want to communicate between networks we will use router question number five what is RJ45 uh RJ45 is basically a type of a connected which is used for ethernet cables now most of most of you also might have seen this particular cable uh this particular cable and this connector so this is ethernet cable and this is having this particular connector this connector is known as RJ45 so I've mentioned this uh purposefully because this a question which was asked to me when when I was fresher and I was attending my interviews let's move to the question number six what is the purpose of TNS so uh DNS is a domain name system and it basically translates domain names into IP addresses now here you can see this facebook.com now what I've did is I did NS lookup so it is going to resolve this I this particular domain name uh into some IP address so it has resolved it to this IP address so it is basically translating the domain name into an IP address now this allows users to access uh because of only DNS only we are we are able to access the websites which are having this human readable names now let's say this is an IP address 16370 14335 now it's very difficult to remember this IP address rather it is very easy to remember the human readable domain name which is ww.facebook.com so this is the main purpose of DNS question number seven what is routing and what are the different types of routing now routing is something uh a process of fing the package from one network to another Network and which is done by a router so a router is going to forward a packet from one network to another Network now how that packet is going going to forward is router is going to have something known as a routing table and in this routing table to reach each and every destination let's say there's a destination one to reach this destination it is going to have a path and it is going to have this path this will be the best path basically of course a rout will be having multiple paths let's say multiple paths it is having to reach a particular destination but it is going to run this routing uh routing thing and it is going to select only one particular path and keep it in this routing table and router is going to refer this routing table and forward the packet according to the routing table referring the routing table now this is perform at layer three that is Network layer and it is performed by router s now what are the different types of routing now when we say different type of routings uh I've mentioned your default routing static routing and dynamic routing default routing is something uh I'll explain let's say this is our router and this router have uh let's say three interfaces interface one interface two and interface three now when I strictly same as router that whatever packets you're going to forward always forward the packets from interface one so that kind of routing is called as default routing and let's say uh if I tell my router if I configure my router with with such configuration where I'm saying my router that whenever you want to reach a 10 Network always use interface one whenever you want to reach 20 network 20.0.0 network all always use uh interface 2 whenever you want to reach 30. 0.0 Network always use interface 3 so this is static configuration this is static routing uh this is static route which I've configured on my router this this requires manual configuration default routing static routing this will require manual configuration of the of the routes whereas Dynamic rout routing is very useful when you have a large networks where it is not possible for your network administrator to manually sit and configure each and every route because it's it's a large Network the number of networks are more so at that time we go for dynamic routing which is possible because of routing protocols now there are multiple routing protocols which are used so this is the uh majorly the three types of routings what is ping ping is this is a question which lot of people know what is Ping but fail to answer so basically ping is a tool I can see to test the layer three reability of the host in a network now this ping also gives you a lot of different information now let's say here I have ped uh this particular IP address that is I've pinged google.com so I'm pinging this particular address now this ping is going to give me the layer reachability means here you can see the packet is successful all these packets are successful you can see here the sent packets and the received packets are four the Lost are zero there's zero percentage of loss that all the packets have been successful so this is a layer 3 reability okay means the Network layer is reachable from the source which is my PC to the destination which is the google.com server so along with this this ping also gives us the information what was the latency now here you can see the average latency to reach is 27 milliseconds you can also see see that the minimum required was 11 milliseconds at a packet uh there there was one packet which reached at 11 milliseconds so there was another packet which reached at 49 milliseconds from source to destination so the average what is figured out is 27 milliseconds so this kind of information also you get the latency information you get uh the test information whether it is reachable or not so this kind of information you get from ping so it's very very useful tool in the life of a network engineer let's move to the next question that is question number nine what is the ad value now ad value basically it is related to routing protocols uh basically it defines the trustworthiness of the routing protocol now when I say trustworthiness of the routing protocol means the routes which are learned by using those routing protocols they will be having certain ad value now let's say uh my router is having uh a route to have two routes to to reach uh let's say there's a route one and Route two to reach a particular destination now route one is having the ad value of uh 25 and route two is having an ad value of 10 so route two will be selected uh as the best path because it is having lesser ad value so lesser ad value means the route is more trusted so here we have the range that is 0 to 255 now 0 is the most trusted vess 255 is not at all trusted is the routes which are having the ad value of 255 will not be used I've also mentioned in question number 10 that what is the ad value of OPF now this kind of questions you will you will face uh this kind of question that what is the ad value of os what is the ad value of brip so most commonly what is the ad value of OPF so the ad value of OPF is 1 1 0 always to remember with this value again I have mentioned ad values of different protocols here you can see I've mentioned zero which is the most trusted now directly connected interface interface so the interface is what something which is the most trusted so it is having the ad value of zero static routing which we discussed this few minutes back its ad value is one bgp have two uh flavors that is external bgp and internal bgp so external bgp have ad value of 20 internal bgp have ad value of 200 eigrp have ad value of 90 of course OPF have the ad value as we know 110 rip have ad value of 120 and unknown is 255 we already discussed this routs will not be used so guys always try to remember this ad values uh interviewer may ask you such question that what is the ad value of different routing protocols so let's move to the next question I think we should have another video maybe I don't want to keep this video more uh uh the length of the video to keep it bit short so we'll continue the next video uh with question number 11 and uh till from 11 to question number 20 we will see in the next video I'll stop here guys uh see you in the next video part two of this uh video till then bye thanks and have a nice day thank you