Routing Protocols

Basic Subnetting

Computing Networks and Hosts

 

 

 

 

Basic Subnetting

 

#There are several ways to find the specifications of a network. 

 

#Here is one simple way to identify the makeup of a network.

 

#Part I concentrates on finding the number of networks vs. the number of hosts.

 

 

Five basic tasks in determining the number of networks and hosts:

 

1.Determine how many hosts or networks are needed.

2.Identify how many bits were “borrowed”.

3.Find the multiplier or “magic number”.

4.Map the network using the multiplier.

5.Find the subnet mask.

 

 

 

#Computing the number of networks is based on the binary equivalents of the following numbers:

128     64    32    16    8    4    2    1

 

 

#Finding Networks

 

-Given 192.168.11. ___

-Find a minimum of 12 networks:

-128     64    32    16    8    4    2    1

-Count right to left

-1 + 2 + 4 + 8 – 1 = 14 networks

 

 

 

#Find “Borrowed” Bits & the “Magic Number”

 

-Determine how many bits were borrowed: 4

128     64    32    16    8    4    2    1

-Count the same number of digits left to right and draw a line.

128     64    32    16    8    4    2    1

-The “magic number” is left of the line:  16

 

 

 

Map the Network

-192.168.11.16

-192.168.11.32

-192.168.11.48

-192.168.11.64

-192.168.11.80

-192.168.11.96

-192.168.11.112

 

 

 

          ---   16 = Network Address

-192.168.11.16

                                    31= Broadcast Address

                                    32= Network Address

-192.168.11.32

                                    47= Broadcast Address

-192.168.11.48

 

 

#Determine the Mask

 

-The mask allows the network to “see” only the network address.

128     64    32    16    8    4    2    1

 

-Add all the numbers left to right, including the multiplier: 240

 

-Class C Mask is 255.255.255.240

 

 

 

Another Example

202.151.37. ____

What class?

Break points = 0 –126       A

                        128 – 191     B

                        192 – 223    C

 

 

 

#Finding Networks

 

202.151.37. ____

-Need 2 Networks:

128     64    32    16    8    4    2    1

3 networks

2 borrowed bits

 

 

 

#Find the Multiplier

 

2 bits were borrowed

128     64    32    16    8    4    2    1

Magic Number = 64

 

 

 

 

 

Map the Network

 

                                         64 = Network Address

   202.151.37.64

                                       127= Broadcast Address

202.151.37.128

 

202.151.37.192

 

26 mask bits + 6 host bits = 32 bits

Max subnets = 3

Max Hosts  =   62

 

 

 

 

 

#Compute the Subnet Mask

 

Subnet mask: 128 + 64 = 192

 

255.255.255.192

 

 

 

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