adam's notes

Public and Private IP Addressing

Public Address

A public IP address is one that can establish a connection with other public IP networks and hosts over the Internet.

  • need public IP address to communicate on the Internet
  • allocation of IP addresses is governed by IANA
    • administered by regional registries and ISPs
    • allocated to customer networks by ISPs
    • there is a shortage of public IPs available for all organizations to have enough for all their computers
      • various mechanisms to work around the shortage of available public addresses
  • hosts communicating over LAN can use a public addressing scheme
    • typically use private addressing instead

Private Address Ranges

Private IP addresses can be drawn from one of the pools of addresses defined in RFC 1918 as non-routable over the internet.

  • use of private addresses is confined to private LANs
  • 3 classes of private addresses:
    • Class A
      • 10.0.0.0-10.255.255.255
    • Class B
      • 172.16.0.0-172.31.255.255
    • Class C
      • 192.168.0.0-192.168.255.255

Address Classes and Default Subnet Masks

Internet Access Using Private Addressing

  • host with private address cannot access the internet directly
  • two ways to facilitate internet access for private addresses:
    1. through a router
      • configured with a single valid public IP address or a block of valid public IP addresses
      • router translates between the private and public address using a process called Network Address Translation (NAT)
    2. through a proxy server
      • fulfills requests for Internet resources on behalf of clients
      • must be configured with a public IP address on the external interface

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