Introduction to the Network

Ip Addressing

Read and memorize the following words:

network — сеть

route traffic — машрутизация трафика

destination — цель, назначение

octets — октеты

private network — частная сеть

host — сервер

adoption — принятие

intermediate methods — промежуточные методы

is kept in confidentiality — хранится конфиденциально

IP address is an identifier for a computer or device on a TCP/IP network and Internet. Networks that use the TCP/IP protocols route traffic based on the IP address of the destination computer or network device. The format of the IP address is 32 bits 4 octets 4 bytes such as 100.100.10.1, 210.100.22.30, 1.10.1.2 these are the examples of the IP address. The format is a 32-bit numeric value written as four numbers and separated by periods.

Each number in the IP address can be between 0 and 255. In your private network, you can assign unique IP address randomly. However, when you want to connect your private network to the Public network such as Internet then you must need a registered IP address to communicate on the internet and to avoid duplicate address. The four numbers in an IP address are used in different ways to identify a particular network. The general internet registries such as APNIC, RIP, NCC and LACNIC assigns internet or IP addresses from the following 3 classes.

1. Class A- IP address from 0-126. It supports 16 million hosts and 126 networks.

2. Class B- IP address from 128-191. It supports 65,000 hosts and 16,000 networks.

3. Class C-IP address from 192-223. It supports 254 hosts and 2 million networks.

The number of unassigned IP address is running out and a new classless scheme called CIDR is replacing the classes based system of the IP address. In this system the A, B and C class is tied to adoption of IPV6.

Every device connected to the Internet must need a unique identifier, which is called an IP address. An IP address is a numeric value separated by periods into four octets. These numbers are usually assigned to the ISPs (internet service providers) within region-based blocks. An IP address can be used to identify a region or a country. An internet user’s geographical location can be determined with the help of an IP address. The number system is generally difficult to remember so the IP address may also assign to a Host name.

The host names are usually easy to remember. In simple words, every website on the internet must bound or mapped with an IP address. At one time ISPs usually issue one IP address to each user. Within each ISP a DHCP (Dynamic host configuration protocol) server is configured, which dynamically assigns IP addresses from a given pool to each user who connects to the ISP. Dynamic IP addresses also limit the ability of a user to host websites, mail servers, ftp server, mail server and web portals.

Understanding IP Addresses Scheme

An IP address is an address that is used to uniquely identify a device or computer on an IP-based network. An IP address is an address used to uniquely identify a device on an IP network. An IP address can be divided into two parts network portion and a host portion. Each IP address is associated with a subnet mask. The 32 bit address is broken into 4 octets and 1 octet=8 bits. Each octet is converted to a decimal and is separated by periods.

For example 0000000000.11111111.00000000.11111111 this is a binary representation of an IP address. Each octet’s decimal value ranges between 0 and 255. The binary octets convert into decimal value. Here you can see that how a binary octet converts into decimal value. The right most bit or least significant bit of an octet will hold a value of 20.

The bit left to that bit will hold a value of 21. This process continues until the left most bit or the most significant bit holds the value of 27. If all the binary bits are one the decimal representation will be like this.

1 1 1 1 1 1 1 1

128 64 32 16 8 4 2 1 (128+64+32+16+8+4+2+1=255)

Now here is a sample conversion of the octet if not all the bits are set of 1.

0 0 1 0 0 0 0 1

0 0 32 0 0 0 0 1 (0+64+0+0+0+0+0+1=33)

In the following example you can see the IP address representation both in binary and decimal values.

64. 2. 135. 19 (decimal)64+2+135+19=220

01001010.00000010.1000111.00010011 (binary)

The octets are broken down to provide a large number of the addressing scheme that can accommodate small and very large networks. There are five different classes of the IP networks. Class A, B, C, D and E. The classes from A to C and mainly in use, D and E are experimental and reserved so they are not commonly in use. Due to the classless inter domain routing (CIDR) these addresses are not practically in use.

Network/Subnet Masks

A network mask helps you which portion of the address identifies the network portion and the host portion of an IP address. The three different classes of the IP addresses have their own default masks as shown below.

Class Subnet Mask

Class A: 255.0.0.0

Class B: 255.255.0.0

Class C: 255.255.255.0

An IP address on a class A network that has not been subnetted would have an address and subnet mask pair such as 10.111.20.1 255.0.0.0. If you want to know in more detail that how a mask help you identify the network and host part of the address simply convert the IP address and subnet mask into the binary numbers.

4.16.15.1= 00000100. 00010000.00001111.00000001

255.0.0.0 = 11111111. 00000000.00000000.00000000

If you have the address and the subnet mask in the binary forms then identifying the network portion and the host portion is very easy. Any address value that has the corresponding subnet mask binary value set to 1 show the network ID. Any address bit that has corresponding subnet mask value to 0 represents the host ID.

4.16.15.1= 00000100.00010000.00001111.00000001

255.0.0.0 = 11111111.00000000.00000000.00000000

What is a Proxy Server?

A proxy server is a computer that offers network and internet access services to the client computers in a network. A client computer connects to the proxy server, requests a connection, services, files and other resources on the other servers. In some cases, the proxy may alter the client’s request and the server’s response for various reasons. By using the proxy server you can hide, conceal and make your network id anonymous by hiding your IP address. To get the anonymous status on the network or Internet, strong intermediate methods are employed like cryptography etc. Examples are remailers, P2P systems etc.

There is a large number of the software available that allows you to hide your IP address with the help of the proxy servers. The well known software for this purpose is Hide IP, Stealth surf, Netconceal, Anonymous surfing, Proxify and Ghost surf.

An IP address is a unique identification number for communication between computer networks, network devices such as computers, fax machines, printers and servers. It is like the number of an apartment or a phone number. IP addresses are of two types Static and Dynamic. Internet service providers’ use dynamic IP addresses and servers usually use static IP address.

The class A of the IP address constitutes almost 50% of all the IP addresses. This class is meant for large networks like the big multinational companies. Class B networks are medium sized like used in the colleges, Universities and other educational and training institutes. Class C IP addresses are usually used for the small companies.

The Regional Internet Registry (RIP) provides the IP addresses based on the geographical distribution. RIP also offers protection against the hackers that try to access the confidential data. All the personal information recorded by the ISP is kept in confidentiality.

Questions:

How many classes of IP addresses do you know?

What is a Proxy Server?

Each number in the IP address can be between?

Communication Devices

Read and memorize the following words:

communication devices — устройства связи

router — маршрутизатор

satellite communication — спутниковая связь

gateway device — шлюз

fiber — волокно

backbone — основа

data store — хранение данных

A network consists of a larger number of the communication devices. The simplest device that is used in the communication is the NIC adapter which is attached with the every computer in a network. If you want to build a LAN, you will need to have computers, hubs, switches, network adapters, UTP/STP cables, routers, internal/external modems, connectors, cable testers and clipping tool.

On the other hand if you need to build WAN, you will need to have routers, switches, dedicated or leased telephone lines such as ISDN lines, frame relay connection and other types of wan communication connections.

There are different communication mediums such as Ethernet cables, copper wire, coaxial cable, fiber optic cables, leased telephone lines and ever air is also a communication medium for the satellite communication. The most common networking medium is the LAN is the Ethernet cable (UTP/STP), which is used in the star topology. Hub is a central device of a network and every computer in a network is directly connected with the hub.

If the hub fails to work, the communication between the computers stops till the hub again starts working. Hub broadcasts the data to its every port, and then finding the destined computer, the data sent toward it. The switch is an advance form of the hub similar in functions but the advanced switches has a switching table in them. An advanced switch stores the MAC address of every attached computer and the data is only sent to the destined computer, unlike the hubs where data is sent to all ports. A router is a key device in the internet communication and wan communication system. A router has software called routing table and the source and destination addresses are stored in the routing table.

A router connects two logically and physically different networks. Router finds the IP address of the next hop (next router) and the data is sent toward it and so on. The well known routers developing companies are Cisco systems, Nortel, DLink and others. Every ISP, banks, corporate offices and multinational companies use routers for LAN and WAN communications and communication in their private networks. A gateway can be device or software in a network.

A gateway device connects the LAN with the Internet. A gateway is directly exposed to the Internet so it should be securely configured and in and out traffic should be monitored. If you are using DSL connection, you must need a DSL modem in your network. The telephone line is connected with the DSL modem and UTP/STP cable attaches your computer with the DSL modem. Modems are the devices that are used to modulate and demodulate the data. They convert analogue signals to digital and digital signals to analogue so that signals can travel on the telephone lines.

There are certain types of the cables that are used to connect two or more computers in a network. Fiber optic cable acts as a backbone between the ISPs and corporate offices. Data travels at the speed of light on the fiber optic cables. The cost and the installation cost of the fiber optic cable is very high but it is becoming very popular in the home networking and LANs also. In the local area networking, 10baseT/CAT5 cable is most commonly in use.

A server is a computer in network that provides services to the client computers such as logon requests processing, files access and storage, internet access, printing access and many other types of services. Servers are mostly equipped with extra hardware such as plenty of external memory (RAM), more data store capacity (hard disks), high processing speed and other features.

Questions:

What is the simplest device that is used in the communication?

What do you need to build WAN?

Are there different communication mediums? What are they?

What is router? What does it have?

What is modem? What does it convert?

In what way are servers mostly equipped?

An Overview of Computer Network Topology

Read and memorize the following words:

topology — топология

mesh — петля

hybrid networks — гибридные сети

recipient — получатель

ultimately — в конечном счете

bus — шина

In Computer Networking “topology” refers to the layout or design of the connected devices. Network Topologies can be physical or logical. In this section I will illustrate on the different types of the topologies. Computer network topologies can be categorized in the following categories:

• bus

• star

• ring

• mesh

• Tree.

Hybrid networks are the complex networks, which can be built of two or more above mentioned topologies.

Bus Topology

Bus topology uses a common backbone to connect all the network devices in a network in a linear shape. A single cable functions as the shared communication medium for all the devices attached with this cable with an interface connector. The device, which wants to communicate send the broadcast message to all the devices attached with the shared cable but only the intended recipient actually accepts and process that message.

Ethernet bus topologies are easy to install and don’t require much cabling and only a main shared cable is used for network communication. 10Base-2 and 10BaseT are two popular types of the Ethernet cables used in the Bus topology. Also, Bus network works with very limited devices. Performance issues are likely to occur in the Bus topology if more than 12-15 computers are added in a Bus Network. Additionally, if the Backbone cable fails then all network becomes useless and no communication fails among all the computers. Unlike in the Star topology in which if one computer is detached from a network then there is not effect on the other computers in a network.

Ring Topology

In ring Network, every computer or devices has two adjacent neighbors for communication. In a ring network, all the communication messages travel in the same directory whether clockwise or anti clockwise. Any damage of the cable of any cable or device can result in the breakdown of the whole network. Ring topology now has become almost obsolete.

FDDI, SONET or Token Ring Technology can be used to implement Ring Technology. Ring topologies can be found in office, school or small buildings.

Star Topology

In the computer networking world the most commonly used topology in LAN is the star topology. Star topologies can be implemented in home, offices or even in a building. All the computers in the star topologies are connected to central devices like hub, switch or router. The functionality of all these devices is different. I have covered the detail of each networking devices in the separate portion of my website. Computers in a network are usually connected with the hub, switch or router with the Unshielded Twisted Pair (UTP) or Shielded Twisted Pair Cables.

As compared to the bus topology, a star network requires more devices & cables to complete anetwork. The failure of each node or cable in a star network, won’t take down the entire network

as compared to the Bus topology.

However if the central connecting devices such as hub, switch or router fails due to any reason, then ultimately all the network can come down or collapse.

Tree Topology

Tree topologies are comprised of the multiple star topologies on a bus. Tree topologies integrate multiple star topologies together onto a bus. Only the hub devices can connect directly with the tree bus and each Hub functions as a root of a tree of the network devices. This bus/star/hybrid combination supports future expandability of the computer networks, much better than a bus or star.

Mesh Topology

Mesh topology works on the concept of routes. In Mesh topology, message sent to the destination can take any possible shortest, easiest route to reach its destination. In the previous topologies star and bus, messages are usually broadcasted to every computer, especially in bus topology. Similarly in the Ring topology message can travel in only one direction i.e clockwise or anticlockwise. Internet employs the Mesh topology and the message finds its route for its destination. Router works in find the routes for the messages and in reaching them to their destinations. The topology in which every devices connects to every other device is called a full Mesh topology unlike in the partial mesh in which every device is indirectly connected to the other devices.

Summary

Topologies are the important part of the network design theory. A better network can be built if you have the knowledge of these topologies and if you know the difference between each topology. Similarly you should have the knowledge of each network device so that you can properly use them according to your network needs. A misconfigured network can result in a waste of time and energy as well as lots of troubleshooting methods to resolve the issue. So the basic understanding of the network topologies and network devices is a must to build a good network.

Questions:

Are hybrid networks complex? Why?

How many different types of topologies do you know?

What's the difference between them?

What is mesh topology?

What can a misconfigured network result?