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What is NAT?
Short for Network Address Translation. NAT is a method whereby many machines can connect to the Internet using the same, single public IP address. Most routers can use this to translate the private IP address of your machines on the LAN to the public IP address of the router. When the replies come back these are translated back and sent to the correct machine. This provides a layer of security as the actual address of your PC is hidden by the router.
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What is LAN?
Short for Local Area Network. These are the machines on your network i.e those that are Local to you. They are usually connected by high speed links and do not need an Internet connection to communicate with each other.
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What is an IP address?
All computers that wish to communicate over the Internet need an IP address. The address you use on the Internet is assigned to you by your ISP and this can either be static or assigned by DHCP. The machines on your LAN can have public or private IP addresses and this can depend on the service provided by your ISP.
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What is a static IP address?
A static IP can be assigned to your connection, making it easy for you to run your own services e.g. webserver, mail server.
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What is a dynamic IP address?
A dynamic IP address will normally change each time you log on to the Internet.
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What is a Public IP address?
This is the IP address that is available on the Internet and is what your router, and possibly your local machine, uses to communicate when you request an Internet resource.
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What is a Private IP address?
This is the IP address of your local machine if you are using NAT. This address is not publicly available and so no direct communication can occur between this machine and the Internet (communication occurs through NAT).
The governing body that controls IP addresses has assigned 3 ranges for private use which you are free to use for any of your machines and routers should not route these addresses on the Internet.
The ranges are:
10.0.0.0 to 10.255.255.255 with mask 255.0.0.0
172.16.0.0 to 172.31.255.255 with mask 255.255.0.0
192.168.0.0 to 192.168.255.255 with mask 255.255.255.0
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What is a Subnet Mask?
This goes with the IP address and tells the machine how to split up the address to identify which network a machine is on.
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What does DHCP mean?
Short for Dynamic Host Configuration Protocol. DHCP is a means of assigning IP addresses automatically thus cutting out the possibility of making a mistake when configuring addresses manually. As this has the potential to change each time you reconnect it makes it harder to run your own services but this is possible through the use of a service like that available from www.dyndns.org
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What does Default Gateway mean?
An address that a machine uses to send all requests to if the request isn’t on the same network as the requesting machine.
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What is a firewall?
A hardware device or software application that sits between your machine and the Internet providing protection for the machines on your LAN. Firewalls can be set to only allow certain TCP ports through and the direction can be specified. This gives much greater control over what is allowed to use your Internet connection.
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What does SPI mean?
Short for Stateful Packet Inspection. This refers to the mode in which a firewall operates. When a request is made to a resource on the opposite side of the firewall all replies to that request are allowed back in even if that port would normally be blocked inbound. The firewall monitors the “conversation” and allows it to occur. This makes it easier to setup the firewall without compromising security.
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Which is better: NAT or SPI?
Using NAT only then traffic is allowed outbound on all ports and thus replies to these requests are allowed back in to the requesting machine. This has the advantage of being easy to set up but is less secure as all outbound traffic is allowed and many Trojans/worms don’t use the standard ports so they would be able to communicate. Using SPI forces you to open ports that you want to allow traffic on and thus cuts out this possibility. This is obviously more secure but more difficult to set up as you need to know which ports to open and you may need to do a little research if that “must have” app doesn’t seem to be working when you enable the firewall.
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What does TCP mean?
Short for Transmission Control Protocol. TCP uses IP to communicate with other machines. Data is sent on a specific port which is why you see references to “opening ports” on a firewall.
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What is an IP?
Short for Internet Protocol. IP is the underlying method by which all machines on the Internet communicate with each other.
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What is Inbound?
Direction of travel of traffic. Inbound is from the Internet to your PC.
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What is Outbound?
Direction of travel of traffic. Outbound is from your PC to the Internet.
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What does Port Mapping or Virtual Server mean?
This is a means of enabling inbound services. Using Port Mapping any inbound connection attempt on a specified port is sent to a machine that you designate.
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