In some cases, you might want to allow a client on an external network to send a request directly to a specific internal node (thus bypassing the normal load balancing server selection). To send a request directly to an internal server, a client normally needs to know the internal nodes IP address, which is typically a private class IP address. Because private class IP addresses are non-routable, you can instead create a network translation address (NAT). A NAT is a feature of BIG-IP® Local Traffic ManagerTM that provides a routable IP address that an external node can use to send traffic to, or receive traffic from, an internal node.
More specifically, a NAT is an address translation object that instructs Local Traffic Manager to translate one IP address in a packet header to another IP address. A NAT consists of a one-to-one mapping of a public IP address to an internal private class IP address.
You can use a NAT in two different ways:

• To translate a private class destination address to a public address – When an external node sends traffic to the public IP address defined in a NAT, Local Traffic Manager automatically translates that destination address to the associated private class IP address, which represents a specific node on the internal network. This translation is hidden from the external node that sent the traffic.
• To translate a private class source address to a public address – You can also use a NAT to translate an internal nodes private class source IP address to a public IP address. This translation is hidden from the external node that receives the traffic.

To summarize, a NAT provides a routable address for sending packets to or from a node that has a private class IP address. When you create a NAT, you can map only one private class IP address to a specific public IP address. That is, a NAT always represents a one-to-one mapping between a private class IP address and a public IP address. If you want to map more than one private class IP address (that is, multiple internal nodes) to a single public IP address, you can create a SNAT instead. To configure and manage NATs, log in to the BIG-IP Configuration utility, and on the Main tab, expand Local Traffic, and click SNATs.