IP Address Classes

• To simplify packet routing, internet addresses are divided into classes.

• The first four bits (bits 0-3) of an address determine its class

• 0xxx = class A
  bits 1-7 define a network
  bits 8-31 define a host on that network
  128 networks with 16 million hosts

• 10xx = class B
  bits 2-15 define a network
  bits 16-31 define a host on that network
  16384 networks with 65536 hosts

• 110x = class C
  bits 3-23 define a network
  bits 24-31 define a host on that network
  2 million networks with 256 hosts

• Class D is a multicast address and class E is reserved

• Orca (131.95.115.204) is class B

• USM uses sub-networking to subdivide its class B networking internally.

• Computers outside USM are not aware of our sub-net scheme.