IPv4 addresses

Goal of Internet Protocol Address

  • Stitch many different networks together
  • Need network-independent, unique address

IPv4

  • An IPv4 address identifies a device on the Internet
  • 32 bits long: a.b.c.d
  • Netmask: apply this mask, if it matches, in the same network

Netmask

  • In addition to an address, a device typically also has something called a netmask.
  • A netmask tells the device which IP addresses are local and which requiring going through an IP router.
  • A netmask is written as a string of consecutive 1s, starting with the most significant bit.
  • You tell whether two computers are in the same network by taking a bitwise AND of their addresses with the netmask. If the resulting addresses are equal, they are in the same network.

Address Structure Historical

  • Originally hierarchical: network + host
  • Network to get to correct netowrk (administrative domain)
  • Host to get to correct device in network (within administrative domain)
  • Originally 3 classes of addresses: class A, class B, class C.

Address Structure Today

  • Classless Inter-Domain Routing
  • Address block is a pair: address,count Counts are powers of 2, specify netmask length 171.64.0.0/16 means any address in the range 171.64.0.0 to 171.64.255.255

IPv4 Address Assignment

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