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Private IP Addresses

Most organisations have far more computers than available IP addresses. Using private IP addresses helps to tackle this issue by allowing companies to have a single Internet gateway with a public IP address. All of the other nodes have private IP addresses. The gateway uses a Network Address Translation (NAT) server to translate the private IP addresses to an address that can be routed across the Internet.

ICANN has reserved sets of IP numbers for private use on the three classes of address. Notice how the recommendation includes non-standard subnet masks for class B and class C private IP ranges.

Private Address Ranges for class A, B and C networks
Class Private IP Address Range Subnet Mask
A 10.0.0.0 to 10.255.255.255 255.0.0.0
B 172.16.0.0 to 172.31.255.255 255.240.0.0
C 192.168.0.0 to 192.168.255.255 255.255.0.0



Activity

  1. Start the command prompt (on Microsoft Windows operating systems select Start/Run and then type in cmd)
  1. Type in ipconfig
  1. Note the IP address of the network connection

If you are using a home network with a router, the chances are that the IP address will be something like 192.168.x.x

If ipconfig is disabled on your network, use the link below to see a typical output from a home network.

ipconfig output

Next: Getting a Public IP Address