Theory 1
Class C Addresses

These were originally reserved for any other organisation that was not large enough to warrant having a class A or B address.  A class C address has the first three bits reserved so the network device can recognise it as such.  The first three bits must show as 110.

The first network number is 192.  All the other network bits are off (0).

128 64 32 16 8 4 2 1
1 1 0 0 0 0 0 0

And the last is 223.  This time all the network bits are on (on the first octet).

128 64 32 16 8 4 2 1
1 1 0 1 1 1 1 1

An example of a class C address is 200.2.1.4 -  200.2.1 is the network address and .4 is a host on that network.  So we can see that there are lots of available network numbers to assign to companies however, we have a limited amount of numbers free to use for the hosts on our networks.

For networks we have to take the first three bits (110) from the first octet giving us 5+8+8= 21 (network bits).

2^21 = 2097152

For the hosts we have 2^8 giving us 255 (only 254 are usable though).

INSPIRATION: If none of this makes any sense at the moment this is only to be expected.  I read the subnetting chapter in a very famous CCNA book for six weeks and it still made no sense to me.  Eventually I worked out the easy way to subnet which I will share with you later.  It is simply a case of reading through this material several (or more) times and it will start to make more and more sense.

 

Leave A Reply (3 comments So Far)


  1. drolls
    373 days ago

    “For networks we have to take the first three bits (011) from the first octet giving us 5+8+8= 21 (network bits)”……….????????

    ——– 011 ……..?????? should it not say 110 ……….?


    • paulwbrowning
      372 days ago

      Fixed that thanks.

      Paul


  2. daddio927
    31 days ago

    Just had an AH-HA moment… I never understood the ip address ranges for class A,B and C networks. The range of addresses reserved for each class seemed very arbitrary. Now that I understand that it is the reserved BINARY BITS that denote a network class, it all makes sense! IT’S ALL ABOUT THE BINARY!! THANK YOU!