Category of Topology

There are four types of Network Topologies:

Mesh Topology

- Every device has a dedicated point, a point link to every other device.

Advantage:
- Eliminating traffic problem
- This topology is robust

Disadvantage:
- Amount of cabling and the number of I/O port is required
-Installation and reconnection are difficult.

Star Topology

- Each device has a directed point to point link only to a central controller (HUB/Switch)

Advantage:

- Does not allow direct between devices
- Less expensive than mesh topology
- Easy to reconfigure and install
- It is robust


Bus Topology

- One long cable act as backbone to link all the device in a network and energy is transformed into heat.

Advantage

-Ease of installation

Disadvantage

-Difficult reconnection and fault isolation

Ring Topology

- Dedicated point to point connection only with two devices on the other side of it. A signal is passed along the ring in one direction.

Advantage:

- Easy to install and reconfigure

Disadvantage:

- Unidirection traffic a break in the ring can disable the entire network

Notation by Class

Octets and Dotted-decimal Notation

The figure below shows how the 32 bits of an IP address are broken down into four octets of eight bits each. Network ID can be called as the Wire ID.

Default Subnets

The default subnet masks are three subnet masks that correspond to the standard Class A, B, and C address assignments.

Why Do We Subnet?

The IP addressing scheme was developed in the late 60s. It was never conceived at that point that so many organizations would want to access what is now called the Internet. The limited addressing space of 32 bits leaves us in a pickle for available bits.

Many people have experienced the same type of problem with voice addresses recently.

For instance, my area code changed from 904 to 850 because the phone company was running out of 904 addressing space. So in effect what the phone company created a sub-area with a different area code. Now the 850 area code is geographically inside what once was the 904 area code.

In the world of IP addressing the same idea was used as a solution to lack of addressing space. We will place one network inside another network. This is called subnetting.

Subnetting

A subnet is a network that falls within a Class A, B, or C network. Subnets are created by using one or more of the Class A, B, or C host bits to extend the network ID.

Subnet Masks

In order for subnetting to work, the router must be told which portion of the host ID should be used for the subnet network ID. It is accomplished by using another 32-bit number, known as a subnet mask.

Those IP address bits that represent the network ID are represented by a 1 in the mask, and those bits that represent the host ID appear as a 0 in the mask. As a result, a subnet mask always has a consecutive string of ones on the left, followed by a string of zeros.

Classifying IP Addresses

Class A addresses
Class A addresses are designed for very large networks. In a Class A address, the first octet of the address is the network ID, and the remaining three octets are the host ID. Each Class A network can accommodate more than 16 million hosts.

Class B addresses
In a Class B address, the first two octets of the IP address are used as the network ID, and the second two octets are used as the host ID. Each Class B address can accommodate more than 65,000 hosts.

Class C addresses
In a Class C address, the first three octets are used for the network ID, and the fourth octet is used for the host ID. With only eight bits for the host ID, each Class C network can accommodate only 254 hosts.

Understanding IP Addresses

An IP address is an address used to uniquely identify a device on an IP network. The address is made up of 32 binary bits which can be divisible into a network portion and host portion with the help of a subnet mask. The 32 binary bits are broken into four octets (1 octet = 8 bits). Each octet is converted to decimal and separated by a period (dot). For this reason, an IP address is said to be expressed in dotted decimal format (for example, 172.16.81.100). The value in each octet ranges from 0 to 255 decimal, or 00000000 - 11111111 binary.

Here is how binary octets convert to decimal: The right most bit, or least significant bit, of an octet holds a value of 20. The bit just to the left of that holds a value of 21. This continues until the left-most bit, or most significant bit, which holds a value of 27. So if all binary bits are a one, the decimal equivalent would be 255 as shown here:

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)

Here is a sample octet conversion when not all of the bits are set to 1.

0 1 0 0 0 0 0 1

0 64 0 0 0 0 0 1 (0+64+0+0+0+0+0+1=65)

And this is sample shows an IP address represented in both binary and decimal.

10. 1. 23. 19 (decimal)

00001010.00000001.00010111.00010011 (binary)

These octets are broken down to provide an addressing scheme that can accommodate large and small networks. There are five different classes of networks, A to E. This document focuses on addressing classes A to C.