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Windows 98, ME, 2000, or XP.

Any computer with a TCP/IP stack and 10BaseT Ethernet port for use with the Ethernet Modem/Router,


What is "NAT"?

When you connect a single computer to the Internet, your ISP allocates you an IP address - a single, unique address which identies your address on the Internet for the duration of your call/connection. All TCP/IP packets sent to/from your computer contain this IP address. Every computer with Internet connectivity must have a unique IP address, so if you have many computers on your LAN, each must have its own local IP address. NAT (Network Address Translation) translates from one IP address to another. In the case of sharing a single public IP address, it is used in a "one-to-many" mode for sharing a single Internet IP address amongst many local PCs which are given IP addresses in a private subnet (IP address range). The NAT system automatically translate the PC's local IP private address into the public IP address being used for Internet access, and back again. Routers and Software-Routers typically provide an NAT facility operating on a "many-to-one IP address" method (i.e. many private IP addresses map to a single public IP address). Despite being a complex operation, NAT generally works well, though not every application will work through a NAT router, so if you have particular requirements, check with your supplier.



What is "Multi-NAT" ?

In the most common situation, NAT is used to translate from a single public IP address to multiple internal private IP addresses; we call that one-to-many NAT (one public IP address to many private ones). You may instead have multiple public IP addresses and want each of those to map directly to multiple internal private IP addresses; this is known as many-to-many NAT. In this way, internal PCs are addressable directly from outside, but on a public IP address rather than their actual internal IP address. Multi-NAT allows this - your ADSL router will allow you to build a table of which public IP address maps to which internal IP client address.

What is "Port Forwarding"?

This will generally only apply if you are intending to run some sort of server on your network, or where a particular application needs port forwarding

When operating a NAT system to share an ADSL feed (see above), all of the computers on your local network (LAN) appear on the Internet under the same IP address. As such, if an incoming packet arrives at your router which is not a response to an outgoing packet, the router will be unable to tell which local PC the data packet is intended for. Port Forwarding enables you to specify a default local PC which is to receive such packets, either always, or based on the 'port number' - the port number identifies the service type. For example SMTP email is always on port 25, so you might choose to forward all incoming packets on Port 25 to your local mail server. Most routers will allow either specific ports or ranges of ports to be forwarded; check with your supplier. It is recommended that you do not open all ports through to a PC as this leaves you more vulnerable to hacking.

What is VPN or Tunneling ?

If you have, say, two LANs, say an office in Riyadh and another in Jeddah, linking them would traditionally involve installing a leased line. This is a permanently connected dedicated data connection. It is expensive and not necessarily fast (the more you pay, the faster it is but this is thousands of Riyals per year even for a 64K connection !). You could also use a dialup connection modems but that's slow too and you are then also paying call charges.

If two computers or networks in different locations are both connected to the Internet, then it is theoretically possible to network them to each other directly via the Internet, using their Internet/Public IP addresses, but it's a terrible idea - your private data, and access to both of the PCs is then passing over the internet in clear form - a very public and insecure network.

VPN is 'Virtual Private Networking' and is a facility where you have software or hardware at each end which sets up a tunnel across the Internet between the two sites. This tunnel is secure and encrypted (a good VPN should use very strong encryption such as IPSec). This means that once the data tunnel is operating, you can pass any data you like through it, securely. Even though the tunnel itself is running through the public Internet, the contents of the tunnel are secure, which means that you can use it for Wide Area Networking (connecting LANs). Consider it like the difference between walking along, carrying a bag full of cash along the pavement (a very public place) compared to driving it along in an armored van with armed guards. In the case of a VPN, the armored van is our tunnel, and the armed guards are the secure encryption (e.g. IPSec). You can have several VPNs running simultaneously so multiple offices can all be linked. As this is all using the Internet, costs are very low compared to leased lines.

That's the good news. The bad news is that VPN does not always work through NAT links, and if you are using a router or software-router to share a 'single user' ADSL USB connection, then you are probably using NAT and therefore your VPN server will not have a real IP address on the Internet or have access to all incoming data ports. The ways to make VPN work are :

1. Use a NAT router that supports VPN 'pass through' for the protocols being used.

2. Have a multi-user, Ethernet ADSL connection with fixed multiple IP addresses (but that costs more than the USB ADSL option)

3. Have the VPN hosts running on the same device/router/PC that is performing the NAT facility for your network and that has the USB modem connected.

4. Use a router which supports VPN and NAT and has a USB host port to connect directly to your existing USB modem