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Hiding Network Computers Gateways

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. Hiding Network Computers Temporary IP Addresses.

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Hiding Network Computers Gateways

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  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.

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

  8. 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.

  9. Local Addresses

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

  11. 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.

  12. 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.

  13. NAT

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

  15. 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.

  16. 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.

  17. 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.

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

  19. 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.

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