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  7. Section 7

Section 7

Table of contents

Class A

  • These class of addresses are assigned to networks with a very large number of hosts.
  • The high-order bit in a class A is always set to zero and the default mask is /8.
  • Its valid networks addresses go from 1.0.0.0 to 126.0.0.0/8.
  • It allows for 126 networks, with 16777214 hosts per network.
  • Both the 0.0.0.0/8 and 127.0.0.0/8 are reserved addresses.

Subnetting

  • Companies noramlly split their /8 address allocation into smaller subnets and allocate these to different offices and types of hosts.
  • For example if they received 15.0.0.0/8, they could allocate the subnet 15.0.1.0/24 to an office and 15.0.2.0/24 to another.

Class B

  • Class B addresses are assigned to medium to large sized networks.
  • The two high order pits in a class B address are always set to binary 1 0.
  • The default subnet mask is /16.
  • Valid networks addresses range from 128.0.0.0 to 192.255.0.0/16.
  • This allows for 16384 networks and 65434 hosts per network.
  • This would also be subnetted in a real world environment.

Class C

  • These classes are used for small networks.
  • The three high-order bits in a class C address are always set to binary 1 1 0.
  • The default subnet mask is /24.
  • Valid network addresses go from 192.0.0.0 to 223.255.255.0/24.
  • This allows for 2097152 networks and 254 hosts per network.

Private addresses

There are valid addresses to be assigned to hosts but they are not routable on the public internet. They were originally designed for hosts in a closed private network with no internet connectivity. The ranges are:

  • Class A: 10.0.0.0 to 10.255.255.255.
  • Class B: 172.16.0.0 to 172.31.255.255.
  • Class C: 192.168.0.0 to 192.168.255.255.

Class D

  • These addresses are reserved for IP multicast addresses.
  • The four high-order bits in a class D address are always set to binary 1 1 1 0.
  • These addresses are not allocated to hosts and there is not default subnet mask.
  • Valid addresses range from 224.0.0.0 to 239.255.255.255.

Class E

  • These addresses are experimental and reserved for future use.
  • The high-order address is set to 1 1 1 1.
  • These addresses are not allocated to hosts and there is not default subnet mask.
  • Valid addresses range from 240.0.0.0 to 255.255.255.255.
  • The last is the broadcast address for this network.