• 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
ClassNetwork octetsOctet RangeDefault MaskApprox. number of possible networksApprox. number of IP aπddresses in each network
A1.x.y.z to 126.x.y.z1-126255.0.0.012616 million
B128.0.x.y to 191.255.x.y128-191255.255.0.016,00065,000
C192.0.0.x to 223.255.255.x192-223255.255.255.02 million254

Reserved IPs

IP Address(es)Function to broadcast messages by TCP/IP background processes. Message is read by every node on the network. through for research or your own computer (loopback address) through 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