By Brian Scheibe Network Address Translation, (NAT), and Port Address Translation(PAT) both map IP address on an internal network to those on an external network. Depending on the type of network you are translating and how many available IP addresses you have, which method of address translation do you use?
If you want to connect a site from the 10.10.10.0 network with a site from the 10.10.20.0, you can use NAT to convert 10.10.10.0 IP addresses into 10.10.20.0 addresses. This will allow hosts on the 10.10.10.0 networks to access data and utilize network resources on the 10.10.20.0. network. This scenario requires that you have enough IP addresses in the 10.10.20.0 network to support all hosts on the 10.10.10.0 network. NAT requires a one to one relationship to translate IP addresses.
PAT attempts to use an original source port number from the internal host to create a unique registered IP address and port combination. Two hosts could be assigned the IP addresses 10.10.10.101 and 10.10.10.101. They could then send and receive traffic from each other using the single public address 123.45.67.89. PAT searches for an alternate source port number if the port number has been allocated. The IP address 10.10.10.100 could therefore access the Internet using the public IP address as well as the source port combination of123.45.67.89.10000. The IP address 10.10.10.101 can access the Internet using the IP address combination of 123.45.67.89.10001.
You must translate the IP addresses of the hosts on the 10.10.10.0 network to an IP address that can be routable over Internet. To use traditional NAT in this scenario you will need to purchase an IP address registered for each host on the internal network. You could also use PAT to translate all IP addresses within your internal network into a single shared IP address that connects with the Internet. PAT, also known as NAT overloading or NAT overloading, uses 16 bit source port numbers to track and map traffic between an internal host computer and the Internet.
As you can see, each acronym has a first letter that denotes the difference between PAT (Port Address Translation) or NAT (Network Address Translation). This should make it easier to remember which one does what. Remember that both NAT (Network Address Translation) and PAT (Port Address Translation) use at least one IP address. PAT, also known as NAT overloading, uses one IP address per client to connect to multiple ports. Standard NAT uses one IP address relationship per client.
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