Network Address Translation

Network Address Translation, sometimes called Network Address Translator (NAT), was originally outlined in RFC 1631 in 1994. This was to allow devices on the inside network the use of private IP addresses that are presently defined in RFC 1918. NAT makes it possible to have a very big internal network with thousands of local addresses represented by a handful of global addresses or possibly a single global address.

basicnat

We will setup a basic static and dynamic NAT configuration.

To the left we have a basic example of how NAT operates.  Starting from the bottom we have our …

  • Inside Local Addresses
  • Outside Local Address
  • Inside Global Address
  • Outside Global Address
Our ISP has given us the following IP range.  189.45.23.56/29, looking at this subnet we can tell that our network starts on the 8th subnet range and this will give us 6 usable addresses

(For simplicity we will not be using subnet-zero)

  • Network ID: 189.45.23.56 (Will always be even)
  • First usable address: 189.45.23.57 (Will always be odd)
  • Last usable address: 189.45.23.62 (Will always be even)
  • Broadcast address: 189.45.23.63 (Remember BrODDcast, always odd)
  • Netmask of: 255.255.255.248

For more subnet information refer to The Last Subnet Doc

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