#interviews question

Top Interview Questions

1) Why we need IP address ?

We need IP address for the device to the identification on the internet basically IP is the source of identification on the internet and if you want to access the internet we need IP address. And on the other side if any one want to communicate in a LAN they need device and if device has no IP address than they cannot communicate with each other.  

2) What is difference between IPv4 and IPv6 ?

IPv4 is the ip address version 4 and this address is 32 bits address in which there are four octets and four octets are equal to 4 bytes. There are 2^32 addresses that are approximately 4.29 billions addresses. And Ipv6 is the upgraded version of the ip address and this address is 128 bits address in which there are trillions of trillions addresses and this version has the 64 bits network part and 64 bits for host part. IPv6 is the solution for the shortage of the IPv4 addresses.

3) Which IP address is used for local testing ?

The ip address 127.0.0.1 is used for the local testing and this address is known as the loopback address and that address is always up it is used for the testing purpose of own system. The loopback is the source of this question (Is our system work correctly ?) .

4) What are the layers of the OSI Model ?

Following are the seven layers of Open System Interconnection Model:

Application Layer  

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical layer

5) Which layer deals with the encoding and decoding ?

Presentation layer is the layer that deals with the encoding and decoding of the data.

6) How many logical ports are and which ports are reserved ?

There are total 65535 logical ports are exist and 0-1023 ports are reserved for the specific purposes and 1024-65535 ports are not reserved these logical ports are that we can use and we find out the service with respect  to the specific port.

7) Which layer use for the checking the availability of the destination ?

Transport layer is the layer that is used to check the availability of the destination and it is also responsible for the establishing, maintaining, and terminating the session.

8) What are port numbers of the FTP, Telnet, and SMTP ?

FTP port number 20,21.

Telnet port number 23

SMTP port number 25.

9) What are the five responsibilities of the transport layer ?

Identifying service.

Segmentation.

Sequencing and reassembling.

Flow control.

Error control.

10) What is difference between the TCP and UDP ?

TCP

TCP stands for the transmission control protocol.

TCP is reliable and connection oriented.

TCP is slower.

UDP

UDP stands for the user datagram protocol.

UDP is unreliable and connectionless.

UDP is faster.

11) What are routing protocols and routed protocols ?

Routing protocols are the protocols that are used for the advertising the networks and there are many routing protocols which are following : RIPv1, RIPv2,IGRP, EIGRP OSPF, BGP, ISIS.

Routed Protocols are the protocols that are used for the sending the user data means packet to one network to the other network basically routed protocol carries user traffic to one network to other which are the following IPX, AppleTalk, and IP.

12) What is the major work of router ?

Router is the networking device that is work on the  network layer and it work on the IP address and the major work of the router is it integrate LAN and WAN. It is unicast device and it determine the best path from source to the destination.

13) What is difference between the console port and auxiliary port ?

Console port is the port that is use for the local configuration when device is near you.

Auxiliary port is the port that is use for the remote configuration when device is not near you.

14) What is three tier hierarchy ?

Three tier hierarchy is the architecture that base on the three layers following are the three layers of this architecture:

Core Layer.

Distribution/Aggregation Layer.

Access Layer.

15) What are the internal components of the router ?

POST: (Power On Self Test).

ROM : (Read Only Memory) store the Internetworking Operating System.

FLASH : Flash is also stores the IOS (Internetworking Operating System).

NVRAM :Store the configuration permanently.

RAM : Store the configuration Temporary.

16) What is DCE and DTE ?

DCE stands for the data communication equipment and it is for the source side at this side we set the clock that is commonly 64000. DTE stands for the data termination equipment and it is for the customer side at this side clock not set.

17) What is Encapsulation and DE encapsulation ?

When data is sent from a upper layer to a lower layer, each layer adds information to data is known as the encapsulation. When data is sent from lower layer to upper layer, each layer will remove information is known as the de-encapsulation.

18) What is difference between the HDLC and PPP ?

HDLC and PPP are the encapsulations HDLC stands for the higher level data link control protocol and HDLC is the cisco proprietary, no support the authentication, no support the compression and error correction and on the other hand PPP stands for the point to point protocol it is a standard protocol and support the authentication, support the compression and error correction .

19) What is convergence ?

Convergence is "to complete the routing table" in other words when each and every ip in the topology is pingable, reachable, and accessible.

20) What are the methods of the routing ?

There are the three methods of the routing that are following :

Static Routing

Default Routing

Dynamic Routing

21) What are the two link state state protocols ?

OSPF (Open Shortest Path First).ISIS (Intermediate System To Intermediate System).

22) How many routers can be managed by the RIPv1 and on which layer RIP work?

Routing Information Protocol is the protocol that can managed the 16 routers means the maximum hops of this protocol is 15. This protocol is the network layer protocol that is work on the application layer.

23) What is split horizon ?

Split Horizon is the built in functionality in Routing Information Protocol to avoid loops basically it is the solution of loop that works like that if one router transmit the advertisements than this router will not receive that advertisements.

24) What is the Multicasting address in RIPv2 ?

The multicasting address in RIPv2 is 224.0.0.9

25) What happen if segments are lost ?

If segments are lost because of the congestion the receiver will acknowledge the last received sequential segment and reply with the reduced window size.

26) What is the original and commercial range of the class A ?

The original range of the class A is 0-127.

The commercial range of the class A is 1-126.

27) What is policy Based Routing ?

Policy based routing can be used to change the next hop IP address for the traffic matching certain criteria. This can be useful to overrule your routing table for certain traffic types.

28) What is difference between the OSPF and ISIS ?

In OSPF

Process ID (Must and Integer).Router ID (Highest IP Priority)Wildcard Bits.Area ID(one router may belongs to multiple areas.

In ISIS

Area Tag (Optional and Alphanumeric).System ID (MAC address and not selected automatically. Wildcard Bits (Not Applicable)Area ID (Globally configured because a router must be in same area)

29) What is Pseudonode in ISIS ?

The DIS is responsible for creating a pseudonode and that is a virtual node created by DIS there are teo responsibilities of the Pseudonode:Create and update a pseudonode LSP that reports links to all neighbours.Create a CSNP (Complete Sequence Number Protocol).

Fig 2:

Pseudonode

30) What are the three types of router in ISIS and describe it roles ?

There are three types of the routers in ISIS:Level 1 (intra area router ) Level 2 (intra area router and it is backbone router).Level 1-2 (has both role)

31) What is dead interval ?

Every X seconds we are going to send a hello packet and if we don't hear any hello packets  from our network for X seconds we declare you "dead" we are no longer neighbors. All other routers who are your neighbors are specified in the hello packet.

32) What are the OSPF LSA Types ?

OSPF uses a LSDB (link state database) and fills this with LSAs (link state advertisement). Instead of using 1 LSA packet OSPF has many different types of LSAs.

LSA Type 1:            Router LSA

LSA Type 2:            Network LSA

LSA Type 3:            Summary LSA

LSA Type 4:            Summary ASBR LSA

LSA Type 5:            Autonomous system external LSA

LSA Type 6:            Multicast OSPF LSA

LSA Type 7:            Not-so-stubby area LSA

33) What is stub area flag ?

Stub area flag: Besides area numbers OSPF has different area types. Both routers have to agree on the area type in order to become neighbors you will become neighbors.

34) Available Subnet 10.1.0.0/16 required hosts 2000 hosts per subnet.

What is new subnet mask ?

What is number of network ?

What are the subnets ranges ?

10.1.0.0 

255.255.0.0

11111111.11111111.00000000.00000000

11111111.11111111.11111000.00000000

2^11=2048 Eleven host bits have been saved.

New Subnet Mask =255.255.248.0

8 is the increment 2048-2 =2046 hosts in one subnets.

2^5 = 32 networks

Subnets Ranges

10.1.0.0-10.1.7.25510.1.8.0-10.1.15.25510.1.16.0-10.1.23.25510.1.24.0-10.1.31.255And so on.

35) Which feature of BGP is for loop avoidance ?

AS-Path is the feature of the Border Gateway Protocol that is use for the loop avoidance and this feature avoid loop like that when one route originated it specify all the AS number where the route come from and if router receive the route that originated by itself then router not accept it.

36) What is AD values of EBGP and IBGP ?

Administrative distance of EBGP is 20.

Administrative distance of IBGP is 200.

37) What are steps in MPLS Domain ?

There are three steps in MPLS domain:

Label insert.

Label swap.

Label pop.

38) What is difference between the FIB and LFIB ?

FIB stands for the Forwarding Information Base and in the FIB there are multiple information like :

Pre Build Cache.

Adjacencies  Table.

Label Information.

LFIP stands for the Label Forwarding Information Base and in LFIB only label information exist.

39) What is frame relay ?

Frame relay is the packet switching technology and it is used to bind the two or more than two routers with a single interface and it mostly used in the Internet Service Provider Side and it is not very costly.

40) What is Ethernet Channel ?

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