Gateway

A Network Gateway is the device that connects your computer, or your LAN, to the Internet – usually it is your ADSL Modem/Router, although it can be a computer on your network.

Network Address Translation - NAT

NAT is an IETF standard that allows an organisation to present itself to the Internet with fewer IP addresses than there are machines on its network. NAT converts the private IP address of a machine on the internal private network to one [or more] public IP addresses for the Internet. It changes the packet headers to the new address and keeps track of each session. When packets come back from the Internet, it performs the reverse conversion to the IP address of the client machine.

Private and Public IP Addresses

The 'Public' IP address refers to the IP address of your router/gateway. This will be allocated to your router by your ISP on a per-session basis. It is the unique number that differentiates your computer or gateway from every other device on the Internet. The public IP address may also be referred to as the WAN Address or as the OUTSIDE IP address.

'Private' IP addresses are those allocated to your LAN PCs by your router (or other DHCP server) and which are ‘hidden' by NAT [above] from the rest of the Internet. So references to your 'private' IP address are to the LAN IP addresses for each node on your network.

Static and Dynamic IP Addressing

Routers use a system called DHCP to allocate an IP address to your PC at start-up. This means that every time your PC is re-started, it will likely have a different IP address within a given range of numbers. If you have set up port-forwarding rules on your router, they will need to be updated to handle the new IP address each time you re-start. Alternatively, you can preset a ‘static IP address' for your PC, meaning the port-forwarding rules do not need to be reset for each start-up.

Check your computer's Help Screens for how to set a Static IP address on your PC. The relevant fields from the Win XP Network Control Panel are shown here:

Also see this link for a Video Tutorial on how to configure Port Forwarding for a NetComm NB1300.

See this page for a BIG LIST of what applications use which ports.

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