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CallTower Information - IP Addressing/Subnet

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IP Addressing:

Overview: 

This document will go over the fundamentals of what an IP address is and does. This study document should help the reader understand how IP addresses and subnets are used.

What is an IP address?

  • An unique identifier given to a computer or device (host) for a TCP/IP network.
  • A 32-bit binary number usually  represented as 4 decimal numbers separated by a period

Example:

206   .   40    .    185  .    73

 

Address in Binary:

11001110.00101000. 10111001.01001001

 

Bits and Bytes:

IP address:

206   .   40    .    185  .    73

11001110.00101000. 10111001.01001001

 

  • A bit – A single 1 or 0. Positive or Negative, Light or No Light

            Example: 11001110

 

  • A byte – 8 Bits. There are 4 bytes in a IPv4 Address.

 

Example: 11001110.00101000.10111001.01001001

Octet = 1 Byte

 

Each bit represents a numerical value:

10000010.

128 | 64 | 32 | 16 | 8 | 4 | 2 | 1

 

What numerical value do the following numbers represent?

00000101

11000000

 

Each address is 32 bits wide

Valid addresses can range from 0.0.0.0 to 255.255.255.255

WHY?

 

Network and Host Addresses
  • Each address consists of two parts
    1. The network address
    2. The host address

The Network Address is considered the Subnet

The host address is the IP assigned to the end point device

 

Which part belongs to the network and which part belongs to the node?

Class A – XXXXXXXX.yyyyyyyy.yyyyyyyy.yyyyyyyy

Class B – XXXXXXXX.XXXXXXXX.yyyyyyyy.yyyyyyyy

Class C – XXXXXXXX.XXXXXXXX.XXXXXXXX.yyyyyyyy

 

X = Network
y = node

 

The Five Network Classes

  1. Class A – binary begins with 0
    • 00000001 (110) to 01111111 (12610)
    • 16,777,214 Hosts
  2. Class B – binary begins with 10
    • 10000000 (12810) to 10111111 (19110)
    • 65,534 Hosts
  3. Class C – binary begins with 110
    • 11000000 (19210) to 11011111 (22310)
    • 254 Hosts
  4. Class D – binary begins with 1110
    • 22410 to 23910
    • Reserved for multicasting
  5. Class E – binary begins with 1111
    • 24010 to 25410
    • Reserved for future use

 

There are three IP network addresses reserved for private networks

  1.             10.0.0.0/8
  2.             172.16.0.0/12 – 172.31.255.255
  3.             192.168.0.0/16

 

These can be used by anyone setting up an internal/home/office network.

Routers will never forward packets coming from these addresses out to the internet. The internet does not recognize these as public IP’s

 

 

Subnetting

 

  • …can be done for a variety of reasons
    • Organization
    • Use of different physical media
    • Preservation of address space
    • Security
    • The most common reason is to control network traffic

 

  • In an Ethernet network, all nodes on a segment see all packets transmitted by other nodes on that segment – collision domain
  • Performance can be adversely affected under heavy traffic loads
  • A router is used to connect IP networks to minimize the amount of traffic each segment must receive – Broadcast Domain

 

Subnet Masking:

 

  • Applying a subnet mask allows you to identify the network and node parts of the address. A router will then determine whether the address is local or remote.
  • Network bits are masked as 1s
  • Node bits are masked as 0s
  • Class A – 255.0.0.0
    • 11111111.00000000.00000000.00000000
  • Class B – 255.255.0.0
    • 11111111.11111111.00000000.00000000
  • Class C – 255.255.255.0
    • 11111111.11111111.11111111.00000000

 

Applying a subnet mask allows you to identify the network and node parts of the address. A router will then determine whether the address is local or remote.

128 | 64 | 32 | 16 | 8 | 4 | 2 | 1

What are the masks below?

11111111.11111111.11111111.00000000

11111111.11111111.11111110.00000000

11111111.111111111.00000000.00000000

11111111.111111111.11111111.11000000

 

To find the subnet mask on a windows machine: This is where it is located:

Picture1.png

 

Determining Hosts/Network ID/Broadcast Address:

 

First IP of the subnet is not used. It is the network ID.

Last IP of the subnet is not used it is the broadcast address.

 

All devices on the same physical segment share a common network ID (subnet mask)

How many hosts are available?

255.255.255.0

255.255.255.128

255.255.254.0

 

The first Host IP of the available hosts is usually configured as the default gateway. That is an industry standard but the default gateway can be configured as any host IP address on the subnet.