1. Hiding Network Computers Gateways
Firewalls are often combined with methods to hide computers to keep them from being visible from the Internet.
A firewall or other gateway device can be used to hide and protect the network behind it.

2. Hiding Network Computers Temporary IP Addresses
Hiding computers is possible because the IP address of a computer does not need not be
Permanent, or
The one used to find it on the Internet.

3. DHCP

4. Hiding Network Computers DHCP
A computer does not need to have the same IP address permanently.
By using the Dynamic Host Configuration Protocol (DHCP), a server can assign IP addresses to computers on a temporary basis.

5. Hiding Network Computers DHCP
Using DHCP to assign temporary IP addresses to computers on a local network has several advantages.

6. Hiding Network Computers DHCP
If the number of IP addresses available is limited, this can hand them out to the currently active computers.

8. Hiding Network Computers DHCP
Computers do not need to be configured with a static IP address by an administrator.

9. Hiding Network Computers DHCP
If a computer’s address changes periodically, it may be harder
to attack it, or
to use it to infect or attack other computers
since it may not be findable once its address changes.

10. Local Addresses

11. Hiding Network Computers Local IP Addresses
Computers can have an IP address that is only available and useful on the local network.

12. Hiding Network Computers Local IP Addresses
For a computer with only a local IP address to get Internet access, it goes through the gateway device.

13. Hiding Network Computers Local IP Addresses
The gateway device uses its own (external) IP address for the Internet communications of those computers with only local addresses.

14. NAT

15. Hiding Network Computers NAT
The gateway device can hide the IP addresses of the internal computers by using Network Address Translation (NAT).

16. Hiding Network Computers NAT
A packet sent
from a computer on the local network
to a computer on the external Internet
will have (among other things)
The sender’s IP address, and
the port number the sender is currently using.

17. Hiding Network Computers NAT
The NAT server, when it sends the packet on to the Internet, will substitute
its own IP address, and
a new port number
for the
IP address, and
Port number
supplied by the local computer.

18. Hiding Network Computers NAT
The NAT server is run on the gateway/router device, so it is in the right place between the local network and the Internet to do this translation.

19. Hiding Network Computers NAT
The new port number helps the NAT server keep track of which machine sent the packet.

20. Hiding Network Computers NAT
When a packet arrives from the Internet, the NAT server notes the port given in the packet.
NAT uses this port to find
the internal IP address, and
real port number
for the local machine.
NAT then substitutes these into the packet, and sends the packet to computer with the correct internal IP address.