Installation guide

10
Private IP address
The Internet uses special Internet addressing schemes to distinguish private local networks from computers
participating in the Internet.
A computer using any of these reserved addresses, will not be visible directly to the Internet – in the same
way your internal phone with its internal extension number cannot be reached directly from the public phone
network without your receptionist switching the call through to that extension.
Your ‘private IP address’ is equivalent to the local extension number of your practice internal phone
network. However, if an attack breaches your network, all your practice addresses are likely to be exposed
to the hacker.
Public IP address
The Internet Service Provider (ISP) connects you to the rest of the Internet via an address that does not
belong to these special reserved private numbers. This is your ‘public IP address’. Your public IP address
is the equivalent of your official, external phone number – that is, the number which people can dial from
anywhere within the public phone network to reach your reception desk.
To be able to use the Internet, a bridge is needed between the private network interfaces and the public
Internet. This is the equivalent of your phone switch box (PABX) in conjunction with an arbitrator, your
receptionist. The phone switch box makes it technically possible to connect the public to the private phone
network, and the receptionist makes sure that no unauthorised caller gets through directly to a specific
extension.
In the Internet world, the equivalent of the PABX phone switch box would be a ‘bridge’ or a ‘router’, and the
equivalent of your receptionist would be your firewall.