The four pitfalls of NAT
There are four basic pitfalls of NAT that everyone should learn. Understand these pitfalls and you will be well-equipped to handle the NAT scenarios that you'll no doubt face:
NAT can be there even when you don't know about it. The Internet does not have to be involved.
Any two techniques to defeat NAT used together will cancel each other out.
Some devices use a SIP ALG (Application Layer Gateway) to defeat NAT.
NAT correction techniques can falsely identify a situation and actually make things even worse.
Become familiar with these pitfalls. They are referenced frequently throughout this chapter.
Let's discuss each of these in more detail:
NAT can be there even when you don't know it. The Internet does not have to be involved.
If you are using home Internet service from your cable or telephone company, or even in some cases a business-class service, they may on occasion use NAT to put all of their customers in a separate network and then translate that network to other...
