الخميس، 19 يناير، 2012

الاسئلة فى انترفيو فى مجال Network and Help Desk and IT Engineer

الاسئلة فى انترفيو فى مجال Network and Help Desk and IT Engineer
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f you are given the IP address can u tell how many computers can be connected?What do you look at

The answer is yes.
This all depends on the type of IP address.That is the class it belongs to.All that is needed to be done is to subnet the given IP adress.


Depending on the address given (Class A, Class B, or Class C) you can determine how many hosts are available. This is also subject to whether the address is classless or classful. If it is classful the a Class C address can have 254 valid hosts, a Class B can have 64,534 and a Class A can allow over 16 million hosts!
If the address is classless then more focus is on the subnet mask. To illustrate a quick example, if you had the subnet address 255.255.255.240, you know that it is a Class C address, but the last octet has been subnetted. Converting 240 into binary gives 11110000. This means that 4 bits were used for subnetting (1111) and four bits are left for addresses (0000). If you did all the possible ranges in binary, starting with 0000 and working all the way til 1111 you see that you get 16 binary instances. Knowing that you cannot use the first and last address you are left with 14, and since the .240 address splits the octet down the middle, you get 14 subnets and 14 valid hosts



What is a different between switch and Hub
HUb: limiteded port compare to switch.less speed compare to switch because

more collision.

Switch: To Avoid collision we use switch. In switch Each Port having own collision Domain.

HUB:Hub is a layer-1 device,in this data transmission in the form of bits.

SWITCH:Switch is a layer-2 device,in this data transmission in the form of frames.

hub:it is a multiple-port repeater.any signals send via the hub is transmitted to all the the ports on the hub..........

switch:it transmit data only to the destination
port


Why should we care about the OSI Reference Model ? What is the main purpose for creating this osi model? why it is a layered model?

The OSI model is conceptual representation of the data communication in a computer network. The layered model is to easily intrpret the process of data communication. Different protocols act at diff layers.
The 7 layers from top are
Application
Presentation
Session
Transport
Network
Data lnink
Physical

This model is standard for data communication. Its an open source its available free.
The purpose of this model is to communicate between two systems.
One layer is independent of other layer

We Shud care about this model cuz this was the 1st model to be created for internet standard.
so this is a internet standard model n all the standard made after this model follow all the rules of this model too

Main purpose to create this model is sending data from one terminal to another terminal without ny loss in data

It's layered model cuz every layer is used for some specific work n one layer is not capable to do all the things.


What are the Advantages and Disadvantages of DHCP?
Advantages
All the IP configuration information gets automatically configured for your client machine by the DHCP server.
If you move your client machine to a different subnet, the client will send out its discover message at boot time and work as usual. However, when you first boot up there you will not be able to get back the IP address you had at your previous location regardless of how little time has passed.
Disadvantage

Your machine name does not change when you get a new IP address. The DNS (Domain Name System) name is associated with your IP address and therefore does change. This only presents a problem if other clients try to access your machine by its DNS name.


Your machine name does not change when you get a new IP address. The DNS (Domain Name System) name is associated with your IP address and therefore does change. This only presents a problem if other clients try to access your machine by its DNS name.


What is Recovery Console?

Recovery Console:That helps you restore your operating system when you cannot start your system.


What is ERD(Emergency Repair Disk)?

Emergency Repair Disk, an ERD is a diskette that creates backups of important system files and settings and is used to help troubleshootand fix issues for Microsoft WINNT and WIN 2000. The ERD is used in conjunction with the Windows repair option and you will be prompted for the diskette when needed. Note: The ERD is not to be confused with a standard boot diskette as it cannot be used alone.

The ERD is capable of performing such checks as:

1. Verifying the boot sector is not corrupt.

2. Repairing any startup files.

3. Locate any missing or damaged system files.


What is the difference between POP3 and IMAP Mail Server?


POP3 is Email clients download your emails onto your computer. Using a specialized email program such as Outlook Express or Apple Mail has the advantage of giving you complete control over your email; every email you receive is placed on your computer and you can keep as many large file attachments as you want.

IMAP is protocol that is being used in ***mail. Checking your email through our ***mail is similar to using Hotmail or YAHOO! Mail. You never actually copy your messages to your computer; in fact, you are looking at them through your *** browser on somebody else's computer. When you are not online, you are not able to see your email.
what is .ost file

n Microsoft Office Outlook 2003, a new offline folder file format is introduced that offers greater storage capacity for items and folders and supports multilingual Unicode data. An offline file folder is used to keep a local copy of your Exchange Server mailbox on your computer. The items in your .ost file are synchronized with the server when a connection is available.

Steps for offline file folder:-

1. On the File menu, click Work Offline.

2. Select or clear the Prompt me at startup so I may choose to work offline or online check box, and then click OK. If you clear the check box, Outlook will automatically start offline if a connection to the server is not available.

3. Click Yes to copy the data from the server to your new Offline Folder file (.ost).


Whatz the difference between DNS and WINS?

DNS- Domain Name Server or Services.

WINS- Windows Internet Name Service.

DNS is resolve the *** site name to IP address or you can say.

In WINS used a file name those is LMhost, this file in the System32, and when we put the ***sit name and its IP address, then it resolve the particular IP address those insert in the LMhost file.

DNS service is used to resolve ***site names to IP address.
WINS is used to identify computers by their computer names in a LAN. Network Administrators can configure a WINS server in a LAN and using this server all machines connected to the LAN can be identified. WINS provides IP to Computer name mapping


How can we create VPN to connect to branch office of the same office.what would be the priliminary requirment?


First of all what is VPN." VPN " stand for Virtual Private Network .Next how it works and where it is used . VPN works when the IP Conficts and IP is conflict because we dont use the PUBLIC IP means the IP we use is may be used by onther Company or Branch then we use VPN it works in the MAC address principal means it doesnot work on the IP it works Over the IP . And COMPUTER ,INTERNET or INTRANET, DHCP is required for the VPN .


We can connect to branch office of the same office thru a vpn by using backbone network provided by a service provider. ISP will provide till customer premises and customer at both sites shud use routers (CPE) to connect to the provider network. Packets are tranferred over the provider network as if it is a private network i.e packets from a specific customer are never forwarded to an interface of a router on the backbone network which is not configured for that VPN. Although data of many customers are forwarded on the backbone, the end user feels as if it is a private network.
The preliminary requirement is that u must order for a leased / dedicated line from ISP.


What is layer-3 switch?

routing depends on ip address : layer 3 s/w

routing depends on mac- address : layer 2 s/w



What is an email client? what is differnce between email client and *** mail?

Email Client
Email clients download your emails onto your computer. Using a specialized email program such as Outlook Express or Apple Mail has the advantage of giving you complete control over your email; every email you receive is placed on your computer and you can keep as many large file attachments as you want.

***mail:
If you host with Needmore Designs, you have a limited amount of space available for your *** mailbox. For daily use, you will want to use an email client. Nevertheless, you might find that you want to check your email while traveling.

Checking your email through our ***mail is similar to using Hotmail or YAHOO! Mail. You never actually copy your messages to your computer; in fact, you are looking at them through your *** browser on somebody else's computer. When you are not online, you are not able to see your email.


what is the vlan ? how it is work

Vlan is virtual Lan...

vlan have 2 main advantages:

1] it is used for security purpose, eg by making vlan u can diffenrentiate group.

2]u can increase collision domain, so collision is reduced


A virtual (or logical) LAN is a local area network with a definition that maps workstations on some other basis than geographic location (for example, by department, type of user, or primary application). The virtual LAN controller can change or add workstations and manage load balancing and bandwidth allocation more easily than with a physical picture of the LAN. Network management software keeps track of relating the virtual picture of the local area network with the actual physical picture
Name three network tools used to determine where a network connectivity is lost between two sites A&B.

PING

TRACEROUTE

PATHPING


Which protocol is used for retrieving mails?

POP3 and IMAP4 are used to retrieve mails.

IMAP4 stores a copy of message on the server whereas POP3 does not.


What is piggy backing?

Piggybacking is gaining access to restricted communication channel by using session that another user has already established. Piggybacking can be defeated by logging off before leaving a workstation or terminal or by initiating a protected mode, such as via a screensaver, that requires re-authentication before access can be resumed


What is the default subnet mask for an ipv6 address ?

255.255.255.255.255.0


What is fragmentation of a packet ?

Frames

Packet data unit(PDU)is called

----------------

segment at transport layer

packet at a network layer

frame at data link and

bit/bytes at physical layer


Maximum Transmission Unit is the largest physical packet size, measured in bytes, that a network can transmit. Any messages larger than the MTU are divided into smaller packets before being sent.
Every network has a different MTU, which is set by the network administrator. On Windows 95, you can also set the MTU of your machine. This defines the maximum size of the packets sent from your computer onto the network. Ideally, you want the MTU to be the same as the smallest MTU of all the networks between your machine and a message's final destination. Otherwise, if your messages are larger than one of the intervening MTUs, they will get broken up (fragmented), which slows down transmission speeds.

Trial and error is the only sure way of finding the optimal MTU, but there are some guidelines that can help. For example, the MTU of many PPP connections is 576, so if you connect to the Internet via PPP, you might want to set your machine's MTU to 576 too. Most Ethernet Networks on the other hand, have an MTU of 1500, which is the default MTU setting for Windows 95.


Name any field of IP header that can prevent a packet to loop infinitely ?

obviously it s time to live(TTL)

it fixes up a time to reach,if it s not reached within that stipulated time,it is being killed by the auto timer...


Under what situations a packet can go into infinite loop in a network ?

if there are more than one way for reaching a particular router from the same source router.


Describe a 3-way TCP/IP Handshake.

To establish a connection, TCP uses a 3-way handshake. Before a client attempts to connect with a server, he server must first bind to a port to open it up for connections: this is called a passive open. Once the passive open is established then a client may initiate an active open. To establish a connection, the 3-way (or 3-step) handshake occurs:

The active open is performed by sending a SYN to the server.
In response, the server replies with a SYN-ACK.
Finally the client sends an ACK back to the server.
At this point, both the client and server have received an acknowledgement of the connection.

when we want to connect to server for communication we need to establish a connection between server and client. The procedure used for this is called 3-way handshake...this is described as follows
1. Initillay the server is ready to accept the incoming connection by binding to local port. This is called passive open.
2. The client now can connect to server by sending SYN J segment to server. The server responds with SYN J+1 and ACK K
3. At the end the client sends ACK K+1 to server..
At this stage we say that client and server are connected

What difference between a directory and active directry

An Directory is the data**** that holds information about component locations, users, groups, passwords, security, and other COM information. Some of this information is currently stored in the Registry, but will eventually (with Windows 2000) be moved to the Active Directory.

The main difference between of Directory and AD is Directory is the repository of data stored but AD not only stores data but have the services by which stored data can be available to the users.


What does CIDR stand for?

CIDR (Classless Inter-Domain Routing) is a way to allocate and specify the Internet addresses used in inter-domain routing


What is a Bridge? When is it used? How is a bridge configured? What are the softwareand hardware components of a bridge?A bridge is an layer 2 device - it works ****d on mac address. bridge is s/w ****d.

It is usually used to bridge 2 networks (or even more in recent times)

Bridge is configured by having the the mac address of the switches connected directly to it.


Can we use static and dynamic routing in one network?

DHCP is only available on newer IOS-****d switches. For example, Catalyst 3550 and 3750 offer DHCP.

Let us take Cisco 2611 router running IOS12.2

To begin, connect the router's Ethernet port to a switch, and connect the switch to a laptop, which will serve as the DHCP client.

To configure Cisco IOS DHCP, follow these steps, which include sample commands:

Configure an IP address on the router's Ethernet port, and bring up the interface. (On an existing router, you would have already done this.)
Router(config)# interface ethernet0/0
Router(config-if)#ip address 1.1.1.1 255.0.0.0
Router(config-if)# no shutdown

Create a DHCP IP address pool for the IP addresses you want to use.
Router (config)# ip dhcp pool mypool

Specify the network and subnet for the addresses you want to use from the pool.
Router(dhcp-config)# network 1.1.1.0 /8

Specify the DNS domain name for the clients.
Router(dhcp-config)#domain-name mydomain.com

Specify the primary and secondary DNS servers
Router(dhcp-config)#dns-server 1.1.1.10 1.1.1.11

Specify the default router (i.e., default gateway).
Router(dhcp-config)#default-router 1.1.1.1

Specify the lease duration for the addresses you're using from the pool.
Router(dhcp-config)#lease 7

Exit Pool Configuration Mode.
Router(dhcp-config)#exit

This takes you back to the global configuration prompt. Next, exclude any addresses in the pool range that you don't want to hand out.

For example, let's say that you've decided that all IP addresses up to .100 will be for static IP devices such as servers and printers. All IP addresses above .100 will be available in the pool for DHCP clients.

Next, enter the ipconfig /renew command on the laptop to receive an IP address. After you have the IP address, enter the ipconfig /all command.


What is the difference between physical address and logical address

A Physical address is a 48-bit flat address burned into the ROM of the NIC cardwhich is a Layer1 device of the OSI model. This iis divided into 24-bit vendor code and 24-bit serial address. This is unique for each system and cannot be changed.

A Logical address is a 32- bit address assigned to each system in a network. This works in Layer-3 of OSI Model. This would be generally the IP address.

Simply we can say that Physical address is MAC address (Media Access Control) which inbuilt and Logical Address is the IP which is given manually.


What is the difference between collision domain and broadcast domain

Broadcast Domain: A set of all devices that recieve broadcast frames originating from any device within the set. Broadcast domains are typically bounded by routers (or, in a switched network, by VLANs) because routers do not forward broadcast frames.

Collision Domain: In Ethernet, the network area within which frames that have collided are propagated. Repeaters and Hubs prpagate collisions, LAN switches and bridges do not.


What is supernetting?why it is used

Supernetting refers to increase host and reduce the subnet's. It mean reduce the network bits and increase the host bits. We do use supernetting because when the PCs in the network increase where we need the more valid IP's in the same network


What is PING utility?.

PING stands Packet Internet Gopher. This is a utility for ensuring connectivity between computers. ICMP protocol works behind this utility. Under it , sending node sends packets to destination node and reply is received if there is proper communication between two.

PING : Packet Internet Gropper
it's a diagnostic utility , which diagnose devices connectivity.
it use ICMP: Internet Control Messaging protocol to send echo requests ( usually 4 packets) and receive echo replies (4 packets)


What is subnetting? why is it used?

A portion of a network that shares a common address component. On TCP/IP networks, subnets are defined as all devices whose IP Address have the same prefix. For example, all devices with IP addresses that start with 100.100.100. would be part of the same subnet. Dividing a network into subnets is useful for both security and performance reasons. IP networks are divided using a subnet mask

Supernetting is dividing the Subnet into different subnets each one of them has its particular required needs , such as Number of Networks and Number of Hosts


What is a VLAN?What does VLAN provide?

A technology called VLAN (Virtual LAN broadcast domains logically segmented on an Ethernet Switch trunking that was once primarily the domain of network switches has now trickled down to the rest of the Data Center to address these issues. Now it is possible for these multi-homing devices to be multi-homing in function without the need for multiple physical network adapters and the additional infrastructure associated with them. VLAN trunking allows a single network adapter to behave as “n” number of virtual network adapters, where ”n” has a theoretical upper limit of 4096 but is typically limited to 1000 VLAN network segments. In the case where a single gigabit Ethernet adapter is trunked in place of using multiple FastEthernet adapters, higher performance at a lower cost while increasing flexibility can be achieved. This really is the best of all worlds. In this article, I will give you an overview of VLAN trunking, how it works what it is used for.

VLAN is a technology by which we can administratively assign different ports of the same layer2 switch to different subnetworks. This is particularly useful when different departments of a company have offices in different floors of the same office. The different departments can be connected via a layer2 switch , which is having configuration for other subnetwork also. So practically the same switch acts as if it is more than one. Packets destined for the specific subnetwork are forwarded to those ports only. But the switch does not make any routing decisions. For interconnecting different subnetworks, routers are needed.
VLAN essentially provides segmentation between different subnetworks.


Difference between the communication and transmission. Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc. Communication means the meaning full exchange of information between two communication media.

Transmission means the transfer of data from the source to the destination.

Communication is the process of sending and recieving data by means of a dta cable that is connected externally.


transmission:transfer of data only in one direction.
communication:transfer of data from both side...
What is the Network Time Protocol

The Network Time Protocol (NTP) is a protocol for synchronising the clocks of computer systems over packet-switched, variable-latency data networks. NTP uses UDP as its transport layer. It is designed particularly to resist the effects of variable latency.


What is RAID

RAID - Redundant Array of Independent / Inexpensive Disks. RAID has many different levels such as 0 1 2 3 4 5 10 01 etc.
We use RAID to protect our data from hardware failure (Hard disk). RAID 5 is used commonly for safeguarding our data.


What are the two types of transmission technology available
1 synchronous txn

2 asynchronous txn


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 are the data units at different layers of the TCP / IP protocol suite?

The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.


What is Project 802?

It is a project started by IEEE to set standards that enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN protocols.

It consists of the following:

802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.

802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.

Media Access Control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used. The modules are

Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).

802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.

802.1 - Network Management (Bridging)
802.2 - EthernetII (Logical Link)
802.3 - Bus topology (CSMA/CD)
802.4 - Token BUS
802.5 - Token Ring
802.6 - For MAN(DQDB -Distributed Queue Dual BUS)
802.7 - BroadBand LAN Networks
802.8 - Optical Fiber Cabling practices
802.9 - Isochronous LAN (Integrated Services LAN)
802.10 - Interoperable LAN Security
802.11 - Wireless wi-fi


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



Difference between bit rate and baud rate?

Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.
baud rate = bit rate / N
where N is no-of-bits represented by each signal shift.


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 attenuation?

The degeneration of a signal over distance on a network cable is called attenuation. What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.


What is NETBIOS and NETBEUI?

NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the Networking hardware from applications.

NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.


What is redirector?

Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.
What is Beaconing?

The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.


What is terminal emulation, in which layer it comes

Telnet is also called as terminal emulation. It belongs to application layer.


What is frame relay, in which layer it comes?

Frame relay is a packet switching technology. It will operate in the data link layer.


What do you meant by "triple X" in Networks?

The function of PAD (Packet Assembler Disassembler) is described in a ******** known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X".


What is SAP?

Series of interface points that allow other computers to communicate with the other layers of network protocol stack.


What is subnet?

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


What is Brouter?

Hybrid devices that combine the features of both bridges and routers.


How Gateway is different from Routers?

A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats.


What are the different type of networking / internetworking devices?

Repeater:
Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the *******ed copy back in to the link.

Bridges:
These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.

Routers:
They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission.

Gateways:
They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.


What is mesh network?

A network in which there are multiple network links between computers to provide multiple paths for data to travel.


What is passive topology?

When the computers simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way.

Example for passive topology - linear bus.


What are the important topologies for networks?


BUS topology:
In this each computer s directly connected to primary network cable in a single line.

Advantages:
Inexpensive, easy to install, simple to understand, easy to extend.

STAR topology:
In this all computers are connected using a central hub.

Advantages:
Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.

RING topology:
In this all computers are connected in loop.

Advantages:
All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.


What are major types of networks and explain?

Server-****d network.
Peer-to-peer network.

Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.

Server-****d networks provide centralized control of network resources and rely on server computers to provide security and network administration.


What is Protocol Data Unit?

The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a
unnumbered frame (U - frame).
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  1. thank you very much for your expensive data

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