Networking Interview Questions

January 30, 2018

Networking Interview Questions

What is ping? Why you use ping?

PING Stands for Packet InterNet Gopher. PING is used for connectivity checking of any network or any host or device of any or other networks.

Routers are always preferrable for routing services. Routers work at which OSI layers?

Router works at network layer for providing routing services between or among several networks.

A gateway works in which layer?

Transport layer of OSI model.

How can you check the connectivity of any network?

By using ping command.

What is a gateway?

A gateway acts a door for the packet to reach the ‘outside’ of the internal network.

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. 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

What is the range of class A address?

0-127 is the range of class A address.

Tell an IP which has class C range. Also tell why that IP is an class C address.

IP of Class C: 193.1.1.1
Why this is a class C address: Class C addresses have the range of 192 - 223

Name a device which can operate at physical layer of OSI model.

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.

What is the major differences between a router and a switch?

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.

Hub operates at which layers of OSI model? Is it wise to use a hub for huge networks? Why or why not?

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.

How many layers are in OSI model? Name them

There are seven layers of OSI model. The layers are:

Application layer
Presentation layer
Session layer
Transport layer
Network layer
Data link layer
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.

Why do you need to use a router?

Router can easily divide the broadcast domain and collision domain. So, to communicate among several networks, routers are used.

What is the second layer of OSI model?

Data Link layer.

Name two network devices which can work as layer 2 device.

Switch and router

What is OSI model?

OSI revers 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.

What is the data unit of Data Link layer?

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

What is the port no of DNS and Telnet?

DNS port no: 53
Telnet port no: 23

What is the port no of SMTP and POP3?

SMPT port no: 25
POP3 port no: 110

What is the functionality of network layer? Name the data unint of network layer.

Functionality of network layer: Path determination and logical addressing
Data unit of network layer: Packet

Which three layers of OSI model is treated as "Media Layers"?

Physical layer, data link layer and network layer are treated as "Media Layers".

What is deadlock?

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.

Mention the advantages and disadvantages of a router.

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.

Mention the private IP address rannge of class B and C.

For Class B: 172.16.0.0 – 172.31.255.255
For Class C: 192.168.0.0 – 192.168.255.255

What is the IP range of class C IP address?

240.0.0.0 255.255.255.255

What is the default subnet mask of class C IP address?

255.255.255.0

Why do you need subnet mask?

Subnet mask is required to divide a large network into several small networks.

Tell the full name: DNS, FTP

DNS: Domain Name System
FTP: File Transfer Protocol

What is the functionality or ARP?

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 its Internet Layer (IP) or Network Layer address is known.

Which one is reliable: TCP or UDP?

TCP is reliable and UDP is an unreliable service.

How DHCP works?

DHCP works by four-steps: (1) IP request, (2) IP offer (3) IP selection and (d) Acknowledgement.

What is POP3? Why you require POP3?

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.

What is the difference between Layer 2 Switch and Layer 3 Switch?

Layer 2 switch is based on MAC addresses which operates on Data Link Layer of OSI mode. And Layer 3 switching is based on network topology table populated and works on Network layer.

Cheat Chart: Some common terms

ARP: Address Resolution Protocol
DNS: Domain Name System
FTP: File Transfer Protocol
HTTP: Hypertext Transfer Protocol
IP: Internet Protocol
NNTP: Network News Transfer Protocol
POP3: Post Office Protocol 3
PPP: Point-to-Point Protocol
SMPP: Short Message Peer-to-Peer
SMTP: Simple Mail Transfer Protocol
TCP: Transmission Control Protocol
UDP: User Datagram Protocol

Cheat Chart: OSI layers

OSI reference model has seven layers:

Application layer
Presentation layer
Session layer
Transport layer
Network layer
Data link layer
Physical layer

Cheat Chart: OSI layers functionality

Application layer: Network process to application
Presentation layer: Data representation and encryption
Session layer: Interhost communication
Transport layer: End-to-end connections and reliability
Network layer: Path determination and logical addressing
Data link layer: Physical addressing
Physical layer: Media, signal and binary transmission

Cheat Chart: TCP/IP reference model

TCP/IP reference model has four layers:

Application
Transport
Internet
Network Access

Cheat Chart: Data Units of OSI layers

Application layer...........Data
Presentation layer.........Data
Session layer.................Data
Transport layer..............Segment
Network layer................Packet
Data link layer...............Frame
Physical layer................Bit

Chear Chart: Default Port Numbers

Service Port No.

FTP -------- 20,21
SSH -------- 22
telnet -------- 23
SMTP -------- 25
DNS -------- 53
DHCP -------- 67,68
TFTP -------- 69
HTTP -------- 80
POP3 -------- 110
NNTP -------- 119
NTP -------- 123
IMAP4 -------- 143
LDAP -------- 389
HTTPS -------- 443
IMAPS -------- 993
RADIUS-------- 1812
AIM -------- 5190

Cheat Chart: Public IP address ranges

Every computer in the Internet has an IP address. There are five types of IP address. In the following table, you will find all the classes of IP address and the class name:

Class Start address Finish Address

A 0.0.0.0 127.255.255.255
B 128.0.0.0 191.255.255.255
C 192.0.0.0 223.255.255.255
D 224.0.0.0 239.255.255.255
E 240.0.0.0 255.255.255.255

Cheat chart: Default subnet mask

In the following section, you will see the default subnet mask of each class:

For Class A: 255.0.0.0
For Class B: 255.255.0.0
For Class C: 255.255.255.0

Cheat Chart: Private IP address ranges

Public IP address is not so much. That's why the concept of private IP arises. In the following, you will find all the private IP address ranges of all classes.

For Class A: 10.0.0.0 – 10.255.255.255
For Class B: 172.16.0.0 – 172.31.255.255
For Class C: 192.168.0.0 – 192.168.255.255

Cheat Chart: Host layers and media layers

Host layers: The upper four layers are known as Host layers. The layers of host layers includes : Application layer, Presentation layer, Session layer and Transport layer.
Media layers: The lower three layers are known as Media layers. The layers of media layers are : Network layer, Data link layer and Physical layer.

· CCNA Practice Questions

· Last Updated on Sunday, 9 March 2008 01:04 Written by admin Thursday, 17 January 2008 04:54

· Multiple Choice questions:

· Q1. Which of the following is Class C IP address?

· A. 10.10.14.118

· B. 135.23.112.57

· C. 191.200.199.199

· D. 204.67.118.54

· Correct Answer: D.

Explanation:
IP addresses are written using decimal numbers separated by decimal points. This is called dotted decimal notation of expressing IP addresses.

· Q2. You have an IP of 156.233.42.56 with a subnet mask of 7 bits. How many hosts and subnets are possible?

· A. 126 hosts and 510 subnets

· B. 128 subnets and 512 hosts

· C. 510 hosts and 126 subnets

· D. 512 subnets and 128 hosts

· Correct answer: C

· Explanation:

· Class B network has the form N.N.H.H, the default subnet mask is 16 bits long.
There is additional 7 bits to the default subnet mask. The total number of bits in subnet are 16+7 = 23.
This leaves us with 32-23 =9 bits for assigning to hosts.
7 bits of subnet mask corresponds to (2^7-2)=128-2 = 126 subnets.
9 bits belonging to host addresses correspond to (2^9-2)=512-2 = 510 hosts.

· Q3. Two sub layers of OSI Data Link layer are which of the following? [Select 2].

· A. Logical Link Control

· B. Data Link Control

· C. Media Access Control

· D. Physical Layer Control

· Correct answer: A,C

· Q4. Match the following:

· A. Repeaters 1. Data Link Layer

· B. Bridges 2. Network Layer

· C. Routers 3. Physical Layer

· Select the best combination:

· A. A —>2, B—>3, C—>1

· B. A—>3, B—->1, C—->2

· C. A—>3,B—–>2, C—->1

· D. A—->1, B—->2, C—->3

· Correct answer: B

· Q5. Which of the following are session layer standards? [Select 2].

· A. NFS

· B. SQL

· C. JPG

· D. MIDI

· Correct answer: A,B

· Q6. Match the corresponding layers of ISO and DoD models?

· DoD Model <---------> ISO OSI Model

· A. Process/Application

· 1. Application

· B. Host-to-Host 2. Presentation

· C. Internet 3. Session

· D. Network Access 4. Transport

· 5. Network

· 6. Data Link

· 7. Physical

· Choose best choice:

· A. A->1+2; B->3+4; C->5; D->6+7

· B. A->1+2+3; B->4; C->5; D->6+7

· C. A->1+2+3; B->4; C->5+6; D->7

· D. A->1+2+3; B->4+5; C->6; D->7

· Correct answer: B

· Q7. What is the command used to add a banner to a Cisco router

· configuration?

· A. add banner

· B. banner motd #

· C. motd banner #

· D. add banner #

· Correct answer: B

· Q8. What is the default administrative distance for RIP?

· A. 100

· B. 120

· C. 0

· D. 200
Correct answer: B

· Q9. The Cisco Catalyst 1900 switches support which three LAN switch types? [Select 3].

· A. Store-and-Forward

· B. FragmentFree

· C. InstaSwitch

· D. FastForward

· Correct answer: A,B,D

· Q10. Which is true regarding VLANs?

· A. VLAN technology uses VLAN switches (layer 2) which is a substitute for routing technology which uses routers.

· B. A VLAN has same collision domain

· C. A VLAN has same broadcast domain

· D. VLANs are less secure with respect to simple switch or Hub networks.

· Correct answer: C

· Q11. Your internet work

· consists entirely of Cisco devices. You have given a command “show cdp neighbors”. In the response, you get “S” under the head “Capability”. What does the letter “S” mean?

· A. It means “Source Route Bridge”

· B. It means “Host”

· C. It means “Switch”

· D. It means “Static”

· Correct answer: C

· Q12. You want to verify the encapsulation type being used at Data Link layer for interface s0. Which command can you use?

· A. Sh ip protocol

· B. sh int s0

· C. sh ip interface

· D. sh processes

· Correct answer: B

· Q13. You want to run 802.2 frame type on your Ethernet interface. Which encapsulation type has to be chosen?

· A. Ethernet_II

· B. 802.2

· C. SAP

· D. SNAP

· Answer is C

· Q14. What does -1 signify in an extended IPX access list?

· A. permit this host

· B. deny this host

· C. permit only this subnet

· D. any host or any network

· Correct answer: D

· Q15. Which command sequence will allow only traffic from network 185.64.0.0 to enter interface s0?

· A. access-list 25 permit 185.64.0.0 255.255.0.0
int s0 ; ip access-list 25 out

· B. access-list 25 permit 185.64.0.0 255.255.0.0
int s0 ; ip access-group 25 out

· C. access-list 25 permit 185.64.0.0 0.0.255.255
int s0 ; ip access-list 25 in

· D. access-list 25 permit 185.64.0.0 0.0.255.255
int s0 ; ip access-group 25 in

· Correct answer: D

· Q16. Which of the following are reference points relevant to ISDN? [Select 2].

· A. T

· B. U

· C. V

· D. X

· Correct answer: A,B

· Q17. Which is true about VLAN Trunk Protocol? [Select 2].

· A. VTP is statically configured and no built in intelligence is available.

· B. VTP provides intelligence for configuring switches across the network.

· C. VTP is not designed to distribute information across the switch fabric.

· D. VTP is designed to distribute information across the switch fabric.

· Correct answer: B, D

· Q18. Which of the following is a term associated with WAN terminology / is a WAN device? [Select all that apply].

· A. Demarc

· B. DSU/CSU

· C. Modem

· D. CPE

· Correct answer: A, B, C, D

· Q19. Which of the following can be used to view the previous command you entered into a Cisco router? [Select 2].

· A. CTRL+F1

· B. The Down Arrow

· C. The Up Arrow

· D. CTRL + P

· Correct answer: C, D

· Q20. What is true about static VLANs? [Choose the best answer].

· A. The VLAN is configured by a TFTP server.

· B. It automatically notify a new network user.

· C. The administrator assigns VLAN by port.

· D. Static VLAN are more appropriate when the switch fabric becomes more complex.

· Correct answer: C

what is subnetting?

We are using subnetting to prevent IP wastage. Subnetting

benefits are 1.Reduced network traffic 2.Optimized network

performance 3.Simplified management 4.Facilitated spanning

of large geographical distances.

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