Remote Access and Securing and Optimizing the Network in Visual Studio .NET

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8 Remote Access and Securing and Optimizing the Network
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Internet Protocol version 6 (IPv6) was created because there were no more IP addresses Although 32 bits sounds like a lot, it s only just over four billion addresses When you consider that big chunks are lost based on how the classes of addresses are divided, there are not enough addresses for each computer to have a valid Internet IP address that enables it to directly communicate over the Internet IPv6 solves this with a few thousand addresses for every square meter of the Earth When change over from IPv4 occurs, NAT will not be necessary But in the meantime, what is it Imagine you have a group of friends down to watch the big game on TV and you want pizza Everyone wants their own choices, but you are the only one who has a phone So, you communicate with the pizza man on behalf of everyone else You take your friends requests and relay them to the pizza man as if you were making the order, and then relay his responses/questions regarding the order back to your friends This is the essence of what NAT is, but without cheese NAT enables organizations to hide their internal IP addresses and indeed to have many more computers using TCP/IP than would be possible if all the addresses had been allocated by an IP Registry If an organization uses NAT, it can use any IP address scheme internally (although there are speci c ranges set aside for internal use, as discussed in 6, TCP/IP ) Only machines connecting directly to the Internet require legitimate addresses, but internal machines can still connect to the Internet thanks to the NAT gateways talking on their behalf and forwarding responses from the Internet to the originator on the local intranet It s also more secure to conceal your internal IP address structure and have all communication via a NAT rewall For example, if a company has 20 computers and they all need Internet connectivity, they would all need legitimate IP addresses But by using NAT, the only machines that would need legitimate Internet IP addresses would be the NAT gateway connected to the Internet That means the company might need only one real address All Internet communication is channeled through that single server (although in reality the company would have several NAT gateways for fault tolerance and load-balancing in larger environments) Figure 8-7 shows this arrangement, with the NAT server performing all queries requested from the internal clients so that the Internet servers see only the IP address of the NAT server There are a number of different NAT types However, in practice, only one is used today Static and dynamic NAT do nothing more than replace the internal IP address of a computer with an Internet routable IP address and send the request on its way However, this requires an equal number of public IP addresses for the number of concurrently connecting internal machines, which is not useful
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Internal computers with 192168/16 class internal only addresses
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FIGURE 8-7 NAT in action
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More popular and useful is port address translation (PAT) also known as overloading, masquerading, and symmetric NAT With this version you have only one public IP address (or possibly more, but only one is necessary) The NAT server reads internal requests to the Internet The source IP address and port of the request are stored in a NAT mapping table on the NAT server The source is changed to the IP of the NAT server s public IP address and a unique port number is added to the NAT mapping table NAT uses this information to track this session When a response comes from the Internet, the NAT server looks at the destination port in the mapping table to nd out which internal machine and port to forward the response to Figure 8-8 shows this process
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