Introduction to Subnetworks Marandola—Lets have some FUN ????

What Is a Subnet? A Series of Networks within a Network Created by subdividing the Host address field and creating a Subnetwork Field All Hosts on a Subnetwork share a common subnetwork address

Why Subnet a Network? Provides Greater Organization of Large Networks (Class A 16 Million Hosts!) Allows Additional Networks (subnets) without applying for additional IPs Gives local administrators more control Provides a Third Level of Hierarchy Reduces the Size of Broadcast Domains

How Do You Create Subnets? Bits are Borrowed from the Host Field –This Creates a Subnet Field in the IP address

Class C Subnets Network Host SHHHHHHS Two Bits Borrowed from the Host Field to form a third layer of hierarchy - A Subnet Field Two Bits must always remain so a maximum of 6 Bits may be borrowed from a Class C network How many bits can be borrowed from a Class B network? From a Class A network?

Class C Subnets Network Host SHHHHHHS The number of Subnets Created is calculated using the following formula: # Subnets Created = 2 # Borrowed Bits

Class C Subnets SHHHHHHS Borrow 2 Bits = 2 2 = 4 Subnets SSSHHHHS Borrow 4 Bits = 2 4 = 16 Subnets SHSHHHHS Borrow 3 Bits = 2 3 = 8 Subnets

Class C Subnets SSSSHHHS Borrow 5 Bits = 2 5 = 32 Subnets Borrow 7 Bits = Cannot Two Host Bits Must Remain SSSSSHHS Borrow 6 Bits = 2 6 = 64 Subnets

How Many Subnets?

If you Borrow 2 Host Bits you do NOT get 4 Subnets. Why? Remember the Network Address and Broadcast Address - Both of these addresses are Reserved, they cannot be used! How Many Subnets? Borrow 2 Bits = 2 2 = 4 Subnets

How Many Subnets?

How Many Hosts/Subnet? Network Host SHHHHHHS The number of Hosts per subnet is calculated using the following formula: # Hosts/Subnet = 2 # Host Bits Remaining # Hosts = 2 6 = 64 hosts/subnet

If there are 6 Host Bits remaining you do NOT get 64 Hosts/Subnet. Why? Each subnetwork has its own Subnetwork Address and Broadcast Address - Both of these addresses are Reserved and cannot be used! Thus only 62 Hosts are available. How Many Hosts/Subnet? 6 Host Bits Remain = 2 6 = 64 Hosts

How Many Hosts/Subnet?

Remember to subtract 2 for the Network Address and Broadcast Address. Remember to subtract 2 for the Subnetwork Address and Subnetwork Broadcast Address. Formulas to Remember! # Subnets Created = 2 # Borrowed Bits # Hosts/Subnet = 2 # Host Bits Remaining

Subnetting is not an easy concept to grasp but you can make life easier on yourself if you will Remember the formulas and rules. Failure to remember this information will guarantee your inability to subnet a network. If you require assistance with Subnetting I will be happy to help. Flash cards work great! Subnetting Made Easier!