IPv4 Address

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• networks in an internetwork need a unique way of identifying each logical network and host
  • at Data Link layer: MAC address
    • only for local delivery of frames
  • at Network layer: IP address
    • used to forward packets
• IP address provides 2 pieces of info:
  • network number (Network ID)
    • common to all hosts on the same IP network
  • host number (Host ID)
    • identifies a host within an IP network

32-bit IPv4 Addressing

• IPv4 address is 32 bits long
  • raw form: 11000110001100110110010000000001
  • subdivided into four group of 8 bits (1 byte)
    • called octets
  • raw form grouped: 11000110 00110011 01100100 00000001
• to make IP address easier to use, it is formatted using dotted decimal notation
  • requires each octet to be converted to a decimal value
  • separated by a period
  • decimal value: 198.51.100.1

Binary-Decimal Conversion

Examples demonstrating binary to decimal conversion:

• in base 2 (binary) digits are either 0 or 1
  • values are powers of 2:
    • memorize these values to perform binary/decimal conversions using columnar method

Convert Binary to Decimal

11000110 represented in base 2

• the first two rows shows the place value of each digit
• third row shows the binary octet
• fourth and fifth row show that where there is a 1 in the octet, the decimal place value is added to the sum

Convert Decimal to Binary

Convert to binary:

• if all bits in an octet are set to 1, then = 255
• an IPv4 address can be any number from 0.0.0.0 to 255.255.255.255
  • some addresses are not permitted
  • some are reserved for special use