Subnets - Networking - Lecture Slides, Slides of Computer Networks

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Subnets in TCP/IP Networks

Chapter Objectives

Subnetting

• Division of a network into subnets
  • For example, division of a Class B address into several Class C addresses
• Some of the host IDs are used for creating subnet IDs

Need for Subnetting

• Classes A and B have a large number of hosts

corresponding to each network ID

• It may be desirable to subdivide the hosts in Class C

subnets

• Often, there is a limitation on the number of hosts

that could be hosted on a single network segment

• The limitation may be imposed by concerns related to the management of hardware
• Smaller broadcast domains are more efficient and

easy to manage

Using Host IDs to Subnet

Class B Network

Subnet 1 Subnet 2 Third octet is now used for subnet IDs

Subnet 3

Subnet Configuration

Subnet ID First Host ID

….. Last Host ID

End of Module

Module

Subnetting Example

Subnetting Structure

Subnet Mask

Sub Net Last Octet Subnet ID

Usable Subnets (6)

Total Number of Subnets and Hosts

• All zeros and ones are not used
  • This has been overcome in the new RFC
• Total number of subnets is 6
• Number of hosts per subnet is 30
• Subnet mask is 255.255.255.
  • 255.255.255. 11100000

End of Module

Overview of the Masking Process

• IP address and subnet masks are used for the masking operation
• The purpose of masking is to identify whether an IP address corresponds to a local host or a remote host
• The mathematical technique used is known as the ANDing process

ANDing Process

• Similar to the AND Boolean operator
• Consider A = B and C
  • A is true only when B and C are true
  • Otherwise, A is false for all other scenarios