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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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5.2 Private addresses

In this part you will look at the problem raised by the use of private IPv4 addresses that are commonly set up for home networks.

Now watch the video below, which is about 4 minutes long.

Private addresses

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Home networks normally use addresses in an IPv4 private address range, most commonly starting 192.168.0.0. Addresses are obtained by DHCP from the home gateway provided by an internet service provider (ISP). (An ISP is the company who provides – and charges for – access to the internet from your home over broadband, optical fibre or satellite.) The ISP has many thousands of customers, each of whom has a home network on which devices might end up with the same IP address.

Since private addresses are not forwarded by routers, using the same IP address in different home networks does not cause clashes. However, private addresses can’t communicate with the internet. The gateway does connect to the internet; it is a router and has two network interfaces: one on the internal LAN and one on the internet. The IP address for the router’s external interface is not private so the router is able to communicate with the internet.

Activity 4 Test yourself

a. 

IP addresses starting 192.168.0.0 are private addresses and are commonly used in home networks.


b. 

ISP stands for Internet Secret Protocol and is used to deliver packets to private addresses.


c. 

Devices can never have the same IP address, even on different home networks.


d. 

ISP is an abbreviation for internet service provider.


The correct answers are a and d.