The document provides a comprehensive overview of interview questions and answers relevant to network engineering, including key concepts such as OSI model layers, network devices distinctions, and protocols. Topics covered include router functionalities, differences between routers and switches, IP address classes, and network troubleshooting techniques. Additionally, it emphasizes the importance of subnet masks and DHCP in network management.

1. Network Engineer Interview Questions
with Answers
The Great Interview Tips for Network
Engineer Job Seekers
Reff:
http://networkingquest.blogspot.com/2011/01/network-engineer-interview-questions.htmlSARMAD ALI

2. Questions and Answers
Q: Routers are always preferable for routing services. Routers work at which OSI layers?
Ans: Router works at network layer for providing routing services between or among several networks.
Q: A gateway works in which layer?
Ans: Transport layer of OSI model.
Q: How can you check the connectivity of any network?
Ans: By using ping command.
Q: What is a gateway?
Ans: A gateway acts a door for the packet to reach the ‘outside’ of the internal network.
Q: What is the range of class A address?
Ans: 0-127 is the range of class A address.
Q: Tell an IP which has class C range. Also tell why that IP is an class C address.
Ans: • IP of Class C: 193.1.1.1
• Why this is a class C address:
Class C addresses have the range of 192 - 223

3. Q: What are the differences among router, switch, bridge and hub?
Router, switch, bridge and hub are network devices. Yet there are some differences among them.
Ans: The main differences are:
• Router: A layer 3 device, can work on physical, data and network layer.
• Switch: A layer 2 device, can work on data link layer
• Bridge: A layer 2 device, can work on data link layer.
• Hub: A layer 1device, just a multi-port repeater and works on physical layer
Q: Name a device which can operate at physical layer of OSI model.
Ans: Hub.
Note: Remember, hub is the device that can work only into the physical layer of OSI model. But
switch, router can also be used instead of a hub. So, all the answers hub, switch or router are all
correct.
Q: What is the major differences between a router and a switch?
Ans: A router can divide the broadcast domain and collision domain. But a switch can only divide the
collision domain. Router can communicate among different networks where as the switch can not
communicate different networks.
Q: Why do you need to use a router?
Ans: Router can easily divide the broadcast domain and collision domain. So, to communicate among
several networks, routers are used.

4. Q: Hub operates at which layers of OSI model? Is it wise to use a hub for huge networks? Why
or why not?
Ans: • Hub operates at only physical layer of OSI model.
• No, it's not so wise to use hub for a huge network.
• Hubs can't divide the broadcast domain or the collision domain. So, if we use hubs then there creates
huge broadcast domain. When there are huge broadcast, the network gets problem time to time. So, it's
not wise to use hubs to support a huge network.
Q: How many layers are in OSI model? Name them?
Ans: There are seven layers of OSI model. The layers are:
1. Application layer
2. Presentation layer
3. Session layer
4. Transport layer
5. Network layer
6. Data link layer
7. Physical layer
Note: You can remember the seven layer model by a simple sentence. Please Do Not Touch Steven's Pet
Alligator. See, the starting of each word forms the layer.
Q: What is the second layer of OSI model?
Ans: Data Link layer.
Q: Name two network devices which can work as layer 2 device.
Ans: Switch and router

5. Q: What is OSI model?
Ans: OSI reveres for Open System Interconnection Reference Model. It is an abstract model for layered
communications and computer network protocol design. There are seven layers of OSI model which,
from top to bottom, are the Application, Presentation, Session, Transport, Network, Data-Link, and
Physical Layers.
OSI model also referred as OSI layered model, OIS layered technology, 7 layer model, OSI seven layer
model, OSI reference model.
Q: What is the data unit of Data Link layer?
Ans: Frame
What are the difference between TCP and UDP?
• TCP: Connection oriented protocol, acknowledged one, Point to point communication.
• UDP: Connection less protocol, unreliable, less traffic
Q: What is the port no of DNS and Telnet?
Ans: • DNS port no: 53
• Telnet port no: 23
Q: What is the port no of SMTP and POP3?
Ans: • SMPT port no: 25
• POP3 port no: 110
Q: What is the functionality of network layer? Name the data unit of network layer.
Ans: • Functionality of network layer: Path determination and logical addressing
• Data unit of network layer: Packet

6. Q: Which three layers of OSI model is treated as "Media Layers"?
Ans: Physical layer, data link layer and network layer are treated as "Media Layers".
Q: What is deadlock?
Ans: Deadlock is a situation when two or more processes are waiting indefinitely for an event that can
be caused by only one of the waiting processes. The implementation of a semaphore with a waiting
queue may result in this situation.
Q: Mention the private IP address rannge of class B and C.
Ans: • For Class B: 172.16.0.0 – 172.31.255.255
• For Class C: 192.168.0.0 – 192.168.255.255
Q: What is the IP range of class C IP address?
Ans: 240.0.0.0 255.255.255.255
Q: Tell the full name: DNS, FTP
Ans: • DNS: Domain Name System
• FTP: File Transfer Protocol
Q: What is the functionality or ARP?
Ans: ARP refers to Address Resolution Protocol. ARP is a computer networking protocol for
determining a network host's link layer or hardware address when only it’s Internet Layer (IP) or
Network Layer address is known.
Q: Which one is reliable: TCP or UDP?
Ans: TCP is reliable and UDP is an unreliable service.

7. Q: Mention the advantages and disadvantages of a router.
Ans: Advantages:
• Router can limit the collision domain and broadcast domain
• Router can function both on LAN & WAN.
• Different media & architectures can be connected among themselves through router.
• Router can determine best path/route for data to reach
• the destination.
• Router can filter the broadcasts.
• For communicating different networks, routers must be used.
Disadvantage:
• Router is more expensive than any other networking devices like Hub, Bridge & Switch.
• Router only work with routable protocols.
• Routing updates consume some bandwidth.
• Increase latency due to greater degree of packet
• filtering.
• Routers function as software based and so it's slower compared to switch.
Q: What is the default subnet mask of class C IP address?
Ans: 255.255.255.0
Why do you need subnet mask?
Subnet mask is required to divide a large network into several small networks.

8. Q: How DHCP works?
Ans: DHCP works by four-steps: (1) IP request, (2) IP offer (3) IP selection and (d) Acknowledgement.
Q: What is POP3? Why you require POP3?
Ans: POP stands for Post Office Protocol. This is used to describe how e-mail clients interact with mail
servers. The POP3 Server is a type of mail server used for incoming mail. POP is only used to receive
messages.
Q: What is the difference between Layer 2 Switch and Layer 3 Switch?
Ans: Layer 2 switch is based on MAC addresses which operate on Data Link Layer of OSI mode. And
Layer 3 switching is based on network topology table populated and works on Network layer.