Networking Interview Questions

Computer Networks Interview Questions

What protocol is used by DNS name servers ?
DNS uses UDP for communication between servers. It is a better choice than TCP because of the improved speed a 

connectionless protocol offers. Of course, 

transmission reliability suffers with UDP.

What is the difference between interior and exterior neighbor gateways? 
Interior gateways connect LANs of one organization, whereas exterior gateways connect the organization to the outside 

world.

What is RIP (Routing Information Protocol)
It is a simple protocol used to exchange information between the routers.


What is OSPF ?
It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an 

Internet's topology to make accurate routing decisions.

What is Kerberos ?
It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to 

prevent intruders from discovering passwords and 

gaining unauthorized access to files.

What is Mail Gateway? 

It is a system that performs a protocol translation between different electronic mail delivery protocols.

Why should you care about the OSI Reference Model

It provides a framework for discussing network operations and design.

What is the difference between routable and non- routable protocols

Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are 

designed to work on small, local networks and cannot be 

used with a router.

What is the difference between TFTP and FTP application layer protocols ? (Asked in IBM Interview)

The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.

The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offered by TCP and so is reliable and secure. It establishes

What is difference between ARP and RARP ?
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used 

by a host or a router to find the physical address of 

another host on its network by sending a ARP query packet that includes the IP address of the receiver.

The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its 

physical address.

What is ICMP ?
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to 

send notification of datagram problems back to the 

sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both 

control and error messages.

What is Bandwidth ?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the 

bandwidth.

What is MAC address ?

The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC 

address is usually stored in ROM on the network 

adapter card and is unique.

What is RAID
A method for providing fault tolerance by using multiple hard disk drives.


What is subnet ?
A generic term for section of a large networks usually separated by a bridge or router.


What is difference between baseband and broadband transmission
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband 

transmission, signals are sent on multiple frequencies, allowing 

multiple signals to be sent simultaneously.

What are the possible ways of data exchange
(i) Simplex (ii) Half-duplex (iii) Full-duplex.

What is point-to-point protocol ?

A communications protocol used to connect computers to remote networking services including Internet service 

providers.

Understanding Windows Server & its Roles.

Understanding Windows Server & its Roles.

What is a Server ?

The term server refers to a machine that is providing a service for other machines, e.g. A computer which shares files on the network would be classed as a file server. For example, A Domain Controller is classed as a server because it is providing a service for the rest of the clients on the network. Windows 2003 can take several different server roles. 

File Server

A File Server stores files and folders that are used by other machines on the network. It can hold applications, text documents, or a user’s My Documents Folder.  For security, many shared folders are housed on file servers. A distributed file system is housed on more than one file server for the sake of fault-tolerance and ease of access.

A Windows XP Professional machine may act as a limited File Server.

A Windows Server 2003 Computer can also act as a file server for different operating systems, e.g. Apple Macintosh.

Print Server

A Print Server is a computer that has a printer attached to it and shares the printer for use on the network.

A Windows XP Professional Machine can be a reasonably capable Print Server.

Application Server

Besides being a Domain Controller, Windows Server 2003 can also be a host to many different services e.g. as a Database Server and a Terminal Server.

Some Common Microsoft Servers:

Microsoft Exchange allows you to setup an e-mail server and also allows you setup a messaging and collaboration system for your company’s network.

Microsoft SQL Server enables you to setup up powerful database servers for your company’s network.

Microsoft ISA Server allows you to setup an Internet Gateway/Proxy Server for your company’s network.

These applications require Windows Server 2003. Their integration with Active Directory allows for tighter security and easier administration.

A Database Server holds a database! This is not just a list of information. It is structured, and dynamic. It needs to be managed, updated, extended and secure, while at the same time being accessible to users.  A dedicated server is required for this.

Remote Administration enables an administrator to manage a server from almost any workstation on the network using Terminal Services. Terminal Services lets workstations use powerful applications housed at the server as if they were installed at that workstation.

Web Servers

A Web Server hosts and manages websites for the Internet or an intranet. Because of the need to manage heavy and burst-mode traffic while maintaining security, a dedicated server is recommended.

Windows 2003 can function as a web server using the Internet Information Services (IIS) service

Windows XP Professional ships with a limited version of IIS which allows a workstation to host a single website.

Networking - What is ARP Cache

ARP is a component which helps to make up the networking functionality of the computer. The ARP allows for computers to be connected to each other in a network using a MAC Address, while still being connected to the wider internet using an internet protocol (IP) address issued by the internet service provider (ISP).

The ARP networking component is best understood as being a repository of information regarding the connection to other computers and networks by using MAC Addresses and IP addresses to engage in networking functionality. Once the computer has communicated with another computer, the response which identifies the computer to be connected to is stored in the ARP Cache. The ARP cache then stores the resolved IP address from the website to be connected to. Eventually, credentials change for successful connection to other computers; as a result, emptying the ARP Cache and rebuilding the file may be a solution to internet and network connection issues.

Rebuilding the ARP cache really refers to clearing or deleting the contents of the cache. Clearing the ARP cache is accomplished by using the Microsoft Windows Command Prompt.
To access the Command Prompt, navigate using the “Start” menu in the taskbar to “Programs”, “Accessories” then “Command Prompt”. At the prompt, type the following without quotations marks: “netsh interface ip delete arpcache” then press the “ENTER” key on the keyboard. The command will delete the entire contents of the ARP cache and rebuild connection and other details needed. With the ARP cache now cleared, all wanted connections can now be made.

For some, however, clearing the ARP cache may have been unsuccessful due to an error in the programming of the Microsoft Windows operating system. In such cases, the user is expected to manually disable the service “Routing and Remote Services”. Navigate to the “Control Panel” from the “Start” menu and open the “Administrative Tools” feature in the Control Panel.
In Administrative Tools, click on “Computer Management” then select “Services and Applications”. Select “Services” and double click the entry “Routing and Remote Services”.
The “Startup Type” should be changed from “Automatic” or “Manual” to “Disabled”. With the service disabled, it will not start after shutdown or reboot. After disabling the service, verify it has stopped by clicking the “Stop” button under the “Service Status” section.

The two aforementioned procedures should be able to allow the ARP cache to be cleared, rebuilt and free from any Microsoft Windows service interruption or intervention allowing for free connectivity between computers, networks and other network peripherals.

Try to maintain the ARP cache regularly to keep the cache free of any future conflicts.

Installing Security Patches in Windows.

What is a computer term called patch?

A patch is an actual piece of object code that is inserted into (patched into) an executable program or A patch is a string of code that fixes a glitch or hole in a computer program. Patches typically are available as downloads over the Internet.

Patch Installation in Windows

Installing Updates in Windows

There are two ways to install Microsoft supplied critical updates under Windows. Manually via Windows Update, or Automatically, via Windows Update.

Manually via Windows Update:

To manually check for and install updates to Windows XP and Vista, log on to an administrative account on your machine. Go to start > All Programs > Windows Update.

In XP:

Internet Explorer will start and go to Microsoft's Windows Update web site. The site will first check for updates to the Windows Update program.



If this site has never been visited from your computer, it will probably want to install an update to the Windows Update program.

Click Yes to accept the update.

Following the update, or if no update is found, the following screen will appear.

Click Scan for updates . The machine will be scanned, and if there are updates available that have not been installed, a screen like the following will appear.

Click Review and install updates . This review will include all the updates classified by Microsoft as Critical Updates and Security Patches . The following screen will appear.

Review the list of updates, and if there is a valid reason not to install one, click the Remove button for that update. Click the Install Now button. A license agreement will pop up.

Click the Accept button. While the update downloads and installs, you will see a window similar to the following.

If you are prompted to reboot the computer when the installation is complete, click OK .

The process of manually checking for and installing critical updates should be done on a frequent, regular basis.

Automatically via Windows Update:

To set up Automatic Updates so that updates will be automatically downloaded and installed on your machine, log on to an administrative account on the machine. Go to start > Control Panel and double click System . Click on the Automatic Updates tab.

Make sure the box is checked in front of: Keep my computer up to date. If this and the rest of the options are set but grayed out, the policy has been implemented at the domain level. You cannot override a domain policy, but you can still manually install updates.

You have three choices. They are fairly self-explanatory. If you choose one of the first two choices, a bubble will pop up in the lower right corner of your screen when updates are available to download/install. Clicking on the bubble will start the process of downloading/installing the update. However, you must be logged on to an administrative account in order to for the bubble to appear.

The third option is what is recommended - Automatically download the updates, and install them on the schedule that I specify . Once this has been set from an administrative account, updates will be downloaded and installed without even logging on, as long as the computer is turned on and booted into Windows at the scheduled time.

Networking Part - II

Classification of computer networks.

Geographical Distance: Computer networks may be classified according to the scale or extent of reach of the network as Local Area Network (LAN), Metropolitan Area Network (MAN) and Wide Area Network (WAN).

                         

Local Area Network (LAN): A network that is limited to a relatively small spatial area such as a room, a single building, a ship, or an aircraft is reffered as LAN. They are sometimes called a single location network. Eg. A small office network or two computers is a house connected using a cable.                           
                             




Metropolitan Area Network (MAN): A network that connects two or more Local Area Networks together but does not extend beyond the boundaries of the immediate town, city, or metropolitan area is called as MAN. eg. A branch office connected to the main office in the same city.


Wide Area Network (WAN):  A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies etc. Eg. Internet or a branch office in India connected to its Corporate office in United States.

Peer to peer network

Advantages:

Low cost as expensive software and hardware are not required.

Easy to implement.

Resource sharing controlled by users.

No need of a dedicated network administrator.

Disadvantages:

Low level of security

Heavy load on computers because of resource sharing

Size of network limited to approximately 10 computers

Client – Server network

Advantages

Strong central security.

Central file storage.

Resource sharing controlled by administrators

Easy management of large number of users.

Disadvantages

Cost of server hardware and software.

Dedicated and well trained network administrator is needed to main this type of architecture.

Client:

A computer on the network that requests resources or services from another computer on a network. In some cases, a client could also act as a server. The term “client” may also refer to the human user of a client workstation.

Server.

A computer on the network that manages shared resources. Servers usually have more processing power, memory, and hard disk space than clients.They run network operating software that can manage not only data, but also users, groups, security, and applications on the network.

Workstation.

A desktop computer, which may or may not be connected to a network. Most clients are workstation computers.

Network operating system (NOS).

The software that runs on a server and enables the server to manage data, users, groups, security, applications, and other networking functions.The most popular network operating systems are Microsoft Windows NT,Windows 2000, Novell NetWare, and UNIX.

Host.

A server that manages shared resources.

Node.

A client, server, or other device that can communicate over a network and that is identified by a unique identifying number, known as its network address.

Topology.

The physical layout of a computer network. Typologies vary according to the needs of the organization and available hardware and expertise.

Transmission Basics:

Data transmission, whether analog or digital, may also be characterized by the direction in which the signals travel over the media.


Simplex, Half-Duplex and Duplex

In cases where signals may travel in only one direction, the transmission is considered simplex. For example, a football coach calling out orders to his team through a megaphone is using simplex communication. In this example, the coach’s voice is the signal, and it travels in only one direction—away from the megaphone’s mouthpiece and toward the team. Simplex is sometimes called one-way, or unidirectional, communication.

In half-duplex transmission, signals may travel in both directions over a medium but in only one direction at a time. Half-duplex systems contain only one channel for communication, and that channel must be shared for multiple nodes to exchange information. For example, Walkie – Talkie.

When signals are free to travel in both directions over a medium simultaneously, the transmission is considered full-duplex. Full-duplex may also be called bidirectional transmission or sometimes, simply duplex.

When you call a friend on the telephone, your connection is an example of a full-duplex transmission, because your voice signals can be transmitted to your friend at the same time your friend’s voice signals are transmitted in the opposite direction to you. In other words, both of you can talk and hear each other simultaneously.

Throughput:

The data transmission characteristic most frequently discussed and analyzed by networking professionals is throughput. Throughput is the measure of how much data is transmitted during a given period of time. It may also be called capacity or bandwidth. Throughput is commonly expressed as a quantity of bits transmitted per second, with prefixes used to designate different throughput amounts. For example, the prefix “kilo” combined with the word “bit” (as in “kilobit”) indicates a 1000 bits per second. Rather than talking about a transmission speed of 1000 bits per second, you would typically say the speed was 1 kilobit per second.

Bandwidth

Bandwidth and throughput are similar concepts, but strictly speaking, bandwidth is a measure of the difference between the highest and lowest frequencies that a medium can transmit. This range of frequencies, which is expressed in Hz, is directly related to throughput. The higher the bandwidth, the higher the throughput.

Baseband

Baseband is a transmission form in which (typically) digital signals are sent through direct current (DC) pulses applied to the wire.This direct current requires exclusive use of the wire’s capacity. As a result, baseband systems can transmit only one signal, or one channel, at a time. Every device on a baseband system shares the same channel.When one node is transmitting data on a baseband system, all other nodes on the network must wait for that transmission to end before they can send data. Baseband transmission supports bidirectional signal flow, which means that computers can both send and receive information on the same length of wire.

Ethernet is an example of a baseband system found on many LAN's.

Broadband

Broadband is a form of transmission in which signals are modulated as radio frequency (RF) analog pulses that use different frequency ranges. Unlike baseband, broadband technology does not involve digital pulses. Nevertheless, the use of multiple frequencies enables a broadband system to access several channels and, therefore, carry much more data than a baseband system.

As you may know, broadband transmission is used to bring cable TV to your home.Your cable TV connection can carry at least 25 times as much data as a typical baseband system (like Ethernet) carries, including many different broadcast frequencies (channels). In traditional broadband systems, signals travel in only one direction.Therefore, broadband cabling must provide a separate wire for the transmission and the receipt of data.

Broadband transmission is generally more expensive than baseband transmission because of the extra hardware involved. On the other hand, broadband systems can span longer distances than baseband.

Networking: Ping TTL Calculation

Ping TTL Calculation.

Hi all I got a discussion in Cisco forum on calculating TTL (Time To Live) when we issue a ping command. Hope this might be of useful to the beginners.

Happy Learning.

Question: How I can calculate TTL in a ping command? I mean, if I've 5 Routers and a PC connected to Router 1 and another PC connected to Router 5. If I issue a ping from the host connected with Router 1 to the host connected in Router 5. How the TTL is calculated in this case?

Best Answer:

TTL is decremented of 1 for each node.

For example: if you have a "chain" 5 routers and you do a ping from Router 1 to Router 5 and TTL is 255 you will reach Router 5 whit TTL value of 251. If you set a TTL of 1 you will reach only the next hop router.

Please post your comments.

The Phonetic Alphabet

The Phonetic Alphabet

Hi all, surprised to see this title in a technical blog like this...., this post is to guide our viewers who are planning/pursing their career in BPO industry or where your voice and accent maters a lot.  

The phonetic alphabet is a very easy to learn and can be immediately employed in a variety of circumstances in order to facilitate improved communication.  Particularly in regard to conveying domain names and passwords via telephone.  The phonetic alphabet is designed to alleviate any confusion on similar sounding letters, such as: B, D, P, T, etc.  Especially these days with Voice Over IP telephone systems, sometimes the call quality can be lacking in clarity and the use of the phonetic alphabet can be the difference between clear and concise communication and total frustration on both ends of the line.

A – Alpha

B – Bravo

C – Charlie

D – Delta

E – Echo

F – Foxtrot

G – Golf

H – Hotel

I – India

J – Juliet

K – Kilo

L – Lima

M – Mike

N – November

O – Oscar

P – Papa

Q – Quebec

R – Romeo

S – Sierra

T – Tango

U – Uniform

V – Victor

W – Whiskey

X – X-ray

Y – Yankee

Z – Zulu

Use of the phonetic alphabet basically consists of replacing the letter you want to say with the actual word from the list above.  So, “A – B – C” is thus said “Alpha – Bravo – Charlie.”  It’s as easy as that!

Next time you find yourself on the phone with native english speaker, consider using the phonetic alphabet to assist with better understanding his/her issue or ticket upon first hearing; 

If you have any suggestions or pro-tips for improving communication, please share them with us in the comments.