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Introduction to Subnetworks

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?.

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Introduction to Subnetworks

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

  2. 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

  3. 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

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

  5. Class C Subnets Network Network Network Host S S H H H H H H 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?

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

  7. Class C Subnets S S H H H H H H Borrow 2 Bits = 22 = 4 Subnets S S S H H H H H Borrow 3 Bits = 23 = 8 Subnets S S S S H H H H Borrow 4 Bits = 24 = 16 Subnets

  8. Class C Subnets S S S S S H H H Borrow 5 Bits = 25 = 32 Subnets S S S S S S H H Borrow 6 Bits = 26 = 64 Subnets Borrow 7 Bits = Cannot Two Host Bits Must Remain

  9. How Many Subnets?

  10. How Many Subnets? Borrow 2 Bits = 22 = 4 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!

  11. How Many Subnets?

  12. How Many Hosts/Subnet? Network Network Network Host S S H H H H H H The number of Hosts per subnet is calculated using the following formula: # Hosts/Subnet = 2# Host Bits Remaining # Hosts = 26 = 64 hosts/subnet

  13. How Many Hosts/Subnet? 6 Host Bits Remain = 26 = 64 Hosts • 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.

  14. How Many Hosts/Subnet?

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

  16. Subnetting Made Easier! • 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!

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