Chapter 12 explored concepts relating to Network Address Translation (NAT), outlining how it can be used to allow privately addressed internal hosts to access Internet resources. Three different NAT techniques were looked at, including static NAT, dynamic NAT, and overloading (PAT). The ability to create mappings to allow Internet hosts to gain access to privately […]

For the purpose of this example, I’m going to assume that we’re using NAT overloading (PAT) to allow our internal clients to access the Internet through a single public IP address. We’ll also create a static inbound mapping to allow external clients to gain access to a web server on our private network. The network […]

While NAT is most commonly looked at as a way to allow internal clients to gain access to the Internet, it can also be used to allow external Internet hosts to gain access to resources on a private network. Recall that by default, a NAT server will drop all packets that are not replies to […]

Overloading is a very popular NAT technique, and is sometimes referred to as Port Address Translation (PAT). Instead of requiring multiple public IP addresses, overloading instead uses a single (or small number) of public address, and differentiates between sessions according to port number. When a client on the internal network wishes to access the Internet, […]

Dynamic NAT works slightly differently in that private and public addresses are not mapped on a one-to-one basis. Instead, a range of public IP addresses is configured on the NAT device, and private internal clients will be mapped to an available address as necessary. The NAT table is built dynamically, avoiding the need for mappings […]

A static NAT implementation is one in which each private internal IP address is mapped to unique public external IP address. This technique involves defining a static NAT table on the router that maps each internal private address to its external public counterpart. Consider the example illustrated in the figure below. It shows a small […]

In Chapter 5 we took a look at how companies have moved to using private IP addresses on their internal networks. The reason for this transition is twofold. Firstly, the rapid growth of the Internet has led to a serious reduction in the number of public addresses available in the IP version 4 address space. […]