• 32 bits
  • Written as four decimal numbers called octets
    • Octet --> 8 bits
    • Each octet can be any number from 0 to 255
  • Divided into two parts
    • Network ID
    • Host ID

Private IPs

  • A company can use private IPs on its private networks
  • IEEE recommends the following:
    • through
    • through
    • through


  • Dividing line between network and host portions is determined by numerical range IP address falls in
  • Class A, B, and C are available for use on the internet
    • Public IP addresses
  • Classes D and E are not available for general use:
    • Class D begins with octets 224-239 --> use for multicasting
    • Class E begins with octets 240-254 --> used for research
Class Network octets Octet Range Default Mask Approx. number of possible networks Approx. number of IP aπddresses in each network
A 1.x.y.z to 126.x.y.z 1-126 126 16 million
B 128.0.x.y to 191.255.x.y 128-191 16,000 65,000
C 192.0.0.x to 223.255.255.x 192-223 2 million 254

Reserved IPs

IP Address(es) Function Used to broadcast messages by TCP/IP background processes. Message is read by every node on the network. Unassigned through Uses for research or your own computer (loopback address) through Used to create APIPA address when a computer configured for DHCP first connects to the network and is unable to lease an IPv4 address from DHCP server.

Subnet Calculations

  • Subnetting
    • Alters the rules of classful IPv4 addressing
    • Called classless addressing
  • Borrow bits that would represent host information in classful addressing and use those bits to represent network information
    • Increase number of bits available for the network ID
    • Reduce number of bits available for identifying hosts
      • Reduce the number of usable host addresses in each network

Computer Science Networking IP Address