Subnetting



Introduction

the ability to create sub-networks and assign IP addresses inside your network needs the knowledge of some technical terms, here's a simple definition of them:
  • Address: The unique number ID assigned to one host or interface in a network.
  • Subnet: a portion of a network that shares a particular subnet address.
  • Subnet mask: a 32-bit combination used to describe which portion of an address refers to the subnet and which part refers to the host.
  • Interface: a network connection.
  • Broadcast address: an IP address that is used to target all systems on a specific subnet network instead of single hosts.
  • CIDR notation: a compact representation of an IP address and its associated network mask.
when you type ip address command on Linux or ipconfig on Windows you get the addressing information. 


Wlan0: presents the wireless interface.
192.168.1.9: presents the address.
/24: presents the CIDR notation.
192.168.1.255: presents the broadcast address.

Understand IP Addresses

An IP address is an address used in order 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.

Given an IP address, its class can be determined from the three high-order bits (the three left-most bits in the first octet). Figure 1 shows the significance of the three high-order bits and the range of addresses that fall into each class. For informational purposes, Class D and Class E addresses are also shown.

Figure1: cisco.com

Calculate Subnets

this is a link to my subnetting cheat sheet, which you can find at googlespreadsheets

 


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