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Discovering computer networks: hands on in the Open Networking Lab
Discovering computer networks: hands on in the Open Networking Lab

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5.6 Implications of NAT

In this part you will consider the implications of NAT, in particular how the combination of NAT and private addresses has enabled home networking to become so common.

Now watch the video below, which is about 2 minutes long.

Implications of NAT

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Network address translation (NAT) is the systematic replacement of IP addresses and port numbers by the router. This can be done to allow devices with IP addresses in a private address range to communicate with the internet. A translation is made as traffic leaves the router and reversed when replies reach the router.

Private addresses are ideal for home networks because devices can be added to the network without needing to obtain new public IP addresses from a registration authority. However, private addresses were intended for use within local networks only. NAT in the gateway router makes it possible for devices with private addresses to communicate with the internet. All devices in the private network effectively share a single address on the internet which reduces the demand for IPv4 addresses.

The combination of private addresses, DHCP and NAT makes it possible for small home networks to be set up easily, without having to allocate public IP addresses. This combination also underpins the rapid rise of home networks and the very large scale of the internet.

Activity 8 Test yourself

5 minutes

Identify the one correct statement in the list below.

a. 

NAT never changes private addresses.


b. 

NAT and private address ranges mean that not all devices need to have unique IP addresses to use the internet.


c. 

You need permission from a registration authority to set up NAT.


d. 

NAT is only applied to packets as they leave a LAN for the internet.


The correct answer is b.