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IPv4

Pv4 history

  • transition from classful to classless

    • classful - divides addresses into 5 groups
      • class A - network ID 8 bits, host ID 24 bits
        • 1st octet 10
      • class B - network ID 16 bits, host ID 16 bits
        • 1st octet 10
      • class C - network ID 24 bits, host ID 8 bits
        • 1st octet 110
      • class D - multicast
        • 1st octet 1110
      • class E - reserved for experimental
        • 1st octet 1111
    • classless - uses variable-length subnet masking, replacing classful
      • 1993 CIDR (Classless Inter-Domain Routing)

  • from IPv4 (1983) to IPv6 (1998)

structure

  • 4 octets of binary digits, represented in decimal 0-255
  • [[subnet]]
  • [[wildcard masks]]

private/public IP's

  • originally created to counter address exhaustion problem
  • public - can be accessed directly over the internet

  • private - only exists w/i local network

    • packet w/ private IP destination will be dropped by routers
    • reserved blocksw
      • class A: 10.0.0.0/8
      • class B: 172.16.0.0/12
      • class C: 192.168.0.0/16

  • translation from Public -> Private, vice versa thru NAT

    • NAT breaks legacy protocols/services relying on end-to-end IP traceability
    • ran out of IPv4 addresses on 11/25/2019