FreeBSD load balancing technology based on NAT

A network address translates into an important feature of an Internet gateway that converts internal and external addresses so that computers with internal addresses can access external networks. The address translation gateway can forward an external address that is owned by an external network access gateway to the computer on which the address maps the internal address.

Therefore, by modifying the address translator so that the address Translation gateway can transform the request evenly into the internal address of multiple internal servers, the computers in the external network communicate with each other in the internal server they have converted.

To implement this load balancing software, you still need to change the original address translator. However, because the address translation tool NATD and its source code are provided under FreeBSD, this task is not complicated. By changing the NATD, the load balancing capability can be achieved on the FreeBSD.

• Layer Fourth Exchange

Because address translation is relatively close to the lower level of the network, it is possible to integrate it into a hardware device, which is typically a LAN switch.

The current advanced LAN switch is beginning to support the so-called layer fourth switching technology, which is to exchange the virtual connection between the IP address and TCP port, and send the packet directly to the corresponding port of the destination computer. By further enhancing its functionality, the switch allows initial connection requests from outside to be linked to multiple internal addresses, which can then be exchanged for the established virtual connections. Therefore, some LAN switches with layer fourth Exchange capability can be used as a hardware load balancer to complete the load balancing of the Web server.

Because layer fourth exchange is based on hardware chip, its performance is very excellent, especially for the speed of network transmission, the speed of exchange far more than ordinary packet forwarding. However, because it is implemented using hardware, it is also less flexible and can only handle load balancing for several of the most standard application protocols, such as HTTP. The current load balancing is mainly used to solve the problem of insufficient processing capacity of the Web server, so the advantages of high network bandwidth brought by the switch are not fully utilized.