IP Address and Class Facts

IP addresses allow hosts to participate on IP based networks. An IP address:

  • Is a 32-bit binary number represented as four octets (four 8-bit values). Each octet is separated by a period.
  • IP addresses can be represented in one of two ways:
    • Decimal (for example 131.107.2.200). In decimal notation, each octet must be between 0 and 255.
    • Binary (for example 10000011.01101011.00000010.11001000). In binary notation, each octet is an 8-digit number.
  • The IP address includes both the network and the host address.
  • Each IP address has an implied address class that can be used to infer the network portion of the address.
  • The subnet mask is a 32-bit number that is associated with each IP address that identifies the network portion of the address. In binary form, the subnet mask is always a series of 1's followed by a series of 0's (1's and 0's are never mixed in sequence in the mask). A simple mask might be 255.255.255.0.

IP addresses have a default class. The address class identifies the range of IP addresses and a default subnet mask used for the range. The following table shows the default address class for each IP address range.

Class

Address Range 

First Octet Range 

Default Subnet Mask

A

1.0.0.0 to 126.255.255.255

1-126
(00000001--01111110 binary)

255.0.0.0

B

128.0.0.0 to 191.255.255.255

128-191
(10000000--10111111 binary)

255.255.0.0

C

192.0.0.0 to 223.255.255.255

192-223
(11000000--11011111 binary)

255.255.255.0

D

224.0.0.0 to 239.255.255.255

224-239
(11100000--11101111 binary)

n/a

E

240.0.0.0 to 255.255.255.255

240-255
(11110000--11111111 binary)

n/a

When using the default subnet mask for an IP address, you have the following number of subnet addresses and hosts per subnet:

  • There are only 126 Class A network IDs (most of these addresses are already assigned). Each class A address gives you 16,777,214 hosts per network.
  • There are 16,384 Class B network IDs. Each class B address gives you 65,534 hosts per network.
  • There are 2,097,152 Class C network IDs. Each class C address gives you 254 hosts per network.
  • Class D addresses are used for multicast groups rather than network and host IDs.
  • Class E addresses are reserved for experimental use.

 

 

Credit: Testout 640-802 CCNA Notes