Basic networking

What is LAN?

LAN is a computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide-area network (WAN). Most LANs connect workstations and personal computers. Each node (individual computer) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions.
What's the difference Between an Intranet and the Internet?

There's one major distinction between an intranet and the Internet: The Internet is an open, public space, while an intranet is designed to be a private space. An intranet may be accessible from the Internet, but as a rule it's protected by a password and accessible only to employees or other authorized users.

From within a company, an intranet server may respond much more quickly than a typical Web site. This is because the public Internet is at the mercy of traffic spikes, server breakdowns and other problems that may slow the network. Within a company, however, users have much more bandwidth and network hardware may be more reliable. This makes it easier to serve high-bandwidth content, such as audio and video, over an intranet.
Define the term Protocol.

Protocol is a standard way of communicating across a network. A protocol is the "language" of the network. It is a method by which two dissimilar systems can communicate. TCP is a protocol which runs over a network.
Define File Transfer Protocol.

File Transfer Protocol (FTP), a standard Internet protocol, is the simplest way to exchange files between computers on the Internet. Like the Hypertext Transfer Protocol (HTTP), which transfers displayable Web pages and related files, and the Simple Mail Transfer Protocol (SMTP), which transfers e-mail, FTP is an application protocol that uses the Internet's TCP/IP protocols. FTP is commonly used to transfer Web page files from their creator to the computer that acts as their server for everyone on the Internet. It's also commonly used to download programs and other files to your computer from other servers.
Networking - What is FTP (File Transfer Protocol)? - Jan 28, 2009, 17:00 pm by Rajmeet Ghai
What is FTP (File Transfer Protocol)?

FTP is File Transfer Protocol. It used to exchange files on the internet. To enable the data transfer FTP uses TCP/IP, FTP is most commonly used to upload and download files from the internet. FTP can be invoked from the command prompt or some graphical user interface. FTP also allows to update (delete, rename, move, and copy) files at a server. It uses a reserved port no 21.
Explain the 7 Layers of OSI.

Layer 1: Physical layer
It represents all the electrical and physical specifications for devices.

Layer 2: Data link layer
It provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical layer.

Layer 3: Network layer
The Network layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks.

Layer 4: Transport layer
It provides transparent transfer of data between end users.

Layer 5: Session layer
It controls the sessions between computers. It connects, manages and terminates the connections between the local and remote application.

Layer 6: Presentation layer
It transforms data to provide a standard interface for the Application layer.

Layer 7: Application layer
It provides a means for the user to access information on the network through an application.

What is a network? What are the different kinds of network? Explain them

A network is a group of computers or nodes connected together. They are connected with each other by communication paths.

Types of Networks:

LAN – Local Area Network connects a group of nodes covering a small physical area. LAN’s are most commonly seen in offices, building etc. LAN’s enable higher transfer rate of data, smaller coverage of area and hence less wiring.

WAN – Wide Area Network connects a group of nodes covering a wide area. WAN typically connects and allow communication between regions or national boundaries. The most common example of WAN is internet.

VPN – Virtual Private Network connects or links nodes in some larger area by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by physical wires. It is used for secure communication through the public internet. VPN alone may not support explicit security features, such as authentication or content encryption.

Intranet – It is a set of networks under the control of a single administrative person. It can be considered as an internal network of an organization. If it is large, web servers are used to provide information to the users.

Extranet – It is a network that restricts itself within a single organization. It can be categorized as WAN, MAN etc. however; it cannot have a single LAN. It must have a connection (at least one) with external network.
What are network topologies? Explain Ring, Bus and Star topology.

A network topology describes the layout of a network. It describes how different nodes and elements are connected to each other. Different types of topology:

a. Ring:-

* All nodes connected with another in a loop.
* Each device is connected to one or more another device on either side.

b. Bus

* All nodes connected to a central and a common cable called as a back bone.
* In bus topology, the server is at one end and the clients are connected at different positions across the network.
* Easy to manage and install.
* If the backbone fails, the entire communication fails.

c. Star

* All nodes connected to a central hub.
* The communication between the nodes is through the hub.
* Relative requires more cables as compared to BUS. However if any node fails, it wont affect the entire LAN.
Explain IP, TCP and UDP.

TCP – Transmission control Protocol is used to establish communication between nodes or networks and exchange data packets. It guarantees delivery of data packets in the order they were sent. Hence it is most commonly used in all applications that require guaranteed delivery of data. It can handle both timeouts (if packets were delayed) and retransmission (if packets were lost). The stream of data is transmitted in segments. The segment header is 32 bit. it is a connectionless communication protocol at the third level (network) of the OSI model.

IP – Internet protocol is used for transmission of data over the internet. IP uses IP addresses to identity each machine uniquely. Message is sent using small packets. The packet contains both the sender and receivers address. IP does not guarantee the delivery in the same order as sent. This is because the packets are sent via different routes. It is a connectionless communication protocol at the third level (network) of the OSI model.

UDP – User Data Protocol is a communication protocol. It is normally used as an alternative for TCP/IP. However there are a number of differences between them. UDP does not divide data into packets. Also, UDP does not send data packets in sequence. Hence, the application program must ensure the sequencing. UDP uses port numbers to distinguish user requests. It also has a checksum capability to verify the data.
What is multicasting?

Multicasting allows a single message to be sent to a group of recipients. Emailing, teleconferencing, are examples of multicasting. It uses the network infrastructure and standards to send messages.

Explain the functionality of PING.

Ping Is particularly used to check if the system is in network or not. It also gives packet lost information. In windows ping command is written as ping ip_address. The output returns the data packets information. The number of packets sent, received and lost is returned by PING
Explain the core naming mechanism, Domain Name System (DNS).

A Domain Name system is used to convert the names of the website on the internet to IP addresses. The domain names for each IP addresses are stored in a database that is distributed across different servers. A domain name space consists of a tree of domain names. The tree has zones. Zones consist of a collection of connected nodes. These nodes are served by a name server. A domain name is usually in the form of mydomain.com. Here, .com is the top level domain. Where as mydomain is the sub domain or subdivision. A host name is a domain name that has one or more IP addresses associated with it.
What is Application layer?

The application layer is located at the top of the TCP/IP protocol layers. This one contains the network applications which make it possible to communicate using the lower layers. The software in this layer therefore communicates using one of the two protocols of the layer below (the transport layer), i.e. TCP or UDP. In computer networking, an application layer firewall is a firewall operating at the application layer of a protocol stack.[1] Generally it is a host using various forms of proxy servers to proxy traffic instead of routing it. As it works on the application layer, it may inspect the contents of the traffic, blocking what the firewall administrator views as inappropriate content, such as certain websites, viruses, and attempts to exploit known logical flaws in client software, and so forth. An application layer firewall does not route traffic on the network layer. All traffic stops at the firewall which may initiate its own connections if the traffic satisfies the rules.
Define DNS

The DNS translates Internet domain and host names to IP addresses. DNS automatically converts the names we type in our Web browser address bar to the IP addresses of Web servers hosting those sites. DNS implements a distributed database to store this name and address information for all public hosts on the Internet.
Define Telnet

Telnet is the main Internet protocol for creating a connection to a remote server.
Define SMTP.

SMTP - Short for Simple Mail Transfer Protocol, a protocol for sending e-mail messages between servers.
What Is a MAC Address?

MAC (Media Access Control) addresses are globally unique addressed that are written into hardware at the time of manufacture. The MAC address is a unique value associated with a network adapter. MAC addresses are also known as hardware addresses or physical addresses. They uniquely identify an adapter on a LAN. MAC addresses are 12-digit hexadecimal numbers (48 bits in length).

MAC vs. IP Addressing

Whereas MAC addressing works at the data link layer, IP addressing functions at the network layer (layer 3). It's a slight oversimplification, but one can think of IP addressing as supporting the software implementation and MAC addresses as supporting the hardware implementation of the network stack. The MAC address generally remains fixed and follows the network device, but the IP address changes as the network device moves from one network to another.
Define Spanning-Tree Protocol (STP)

Spanning-Tree Protocol (STP) as defined in the IEEE 802.1D is a link management protocol that provides path redundancy while preventing undesirable loops in the network. For an Ethernet network to function properly, only one active path can exist between two stations. Loops occur in networks for a variety of reasons. The most common reason you find loops in networks is the result of a deliberate attempt to provide redundancy - in case one link or switch fails, another link or switch can take over.
What is VPN?

A VPN is a service that offers secure, reliable connectivity over a shared public network infrastructure such as the Internet. VPNs maintain the same security and management policies as a private network. They are the most cost effective method of establishing a virtual point-to-point connection between remote users and an enterprise customer's network.
How would you define IP address?

IP address or Internet Protocol address is the address of a device attached to an IP network (TCP/IP network). It is a must for every client, server and network device to have a unique IP address for each network connection (network interface). Every IP packet contains a source IP address and a destination IP address. As a device moves from one network to another, its IP address changes.
Computers using the TCP/IP for communication are uniquely identified by a 32 bit address called as an IP address. The routers use the IP address information to forward the packet to the destination computer.

IP addresses are categorized as:

Private address: these IP addresses are used exclusively within a private network and not for public to see.

Public Address: these are registered IP addresses used for public.

Each IP address has a network address and a host address. IP addresses are expressed in four sets of three numbers, separated with dots. Each set is called as an octet because when converted to binary; it denotes eight binary.

Difference between Static and Dynamic IP.
Static IP is also called as permanent address assigned to each device in a network, whereas Dynamic IP, a temporary address assigned to the device via DHCP software. IP address assigned to your service by your cable or DSL Internet provider is typically dynamic IP. In routers and operating systems, the default configuration for clients is dynamic IP

What is Network Address Translation?
Network Address Translation acts as an agent between the Internet and a local network. It is a dynamic method which is used to minimize Internet connectivity needs. Network address translation describes the rewriting of the Internet Protocol (IP) addresses of data packets so that multiple transmissions require only one IP address
What is subneting?

Subnet adds one level to the way IP address is represented. It logically organizes the network. For instance, it can logically group computers belongs to the finance department.
Define Address Resolution Protocol.

Address Resolution Protocol ARP, is responsible for mapping an IP address to its corresponding physical network address. It is mostly seen on Ethernet network.
Explain Maximum Transfer Unit, MTU.

MTU specifies the largest amount of data that can be transferred across a network

What is Routing Protocol?

Routing protocol is the way to send routing information between any routers in an autonomous system.
When a source sends a packet to a destination, this packet has a specific path or route it follows. Different routing protocols are used to find the shortest path to the destination. The protocols maintain routing tables. Routing tables consist of a set of rules used to determine where these packets will travel. When a packet is received, a network device examines the packet and matches it to the routing table entry providing the best match for its destination. The packet keeps hopping until it reaches its destination.
Define broadcast domain.

It is a logical area in a computer network where any computer connected to the network can directly transmit to any other computer in the domain without having to go through a routing device.