DNS Load Balancing

Load balancing is a computer technology for distributing information requests across multiple resources. For example, multiple connections to a website or host record may be serviced by distribution of the requests to multiple servers containing the same web content, but located at different IP addresses. Each time a request is made for connection to the domain name, the authoritative name server for the domain sends all IP addresses associated with the name back to the client or requester.

Management is accomplished in what is called a "round robin" fashion. This means that the authoritative name server changes the order of the IP contained in the response to the client, randomizing the order or placing the addresses into a sequential order. A client normally connects to the first address on the list, and so by reorganizing the list, the server ensures that requests for access to the domain name are directed to multiple end servers. In this scheme, IP addresses are handed out in sequential order, meaning that the first client request gets the first IP record, the second request the second record, and so on throughout the list. This is a simple method to implement, but in some cases it is deficient for various reasons. Clients do manage connections by shifting from an attempted connection with a non-responsive resource to the next available resource so that generally speaking a connection will ultimately succeed.

The operation of DNS load balancing is fairly simple in practice. Generally there will be several so-called "front end servers," each of which has its own IP address. All of the servers will then connect physically through a network to the primary intended resource on the "backend." The list of IP addresses is that list which is delivered to Internet clients making a request for access. The IP address is, of course, the location on the Internet where the resource is physically located and accessible. The list is randomized or placed into sequential order, and each client will attempt to form a connection with the first IP address on the list. If that connection fails, the client will attempt to connect to the next IP address, and then the next, and so on.

There are various limitations to DNS load balancing which may prevent its use in some cases. DNS load balancing is not the only method of load balancing. Other methods include direct routing, involving changing the MAC address of the incoming data packet, and network address translation (NAT) load balancing, involving translation of requests through a load balancer. Limitations to DNS load balancing include most importantly that it is not possible through this method to ensure even distribution across all receiving servers.

DNS management tools can also be used in the load balancing process. DNS management tools allow for monitoring of IP address availability to ensure ready connectivity. There are also DNS management tools designed to identify MAC addresses of devices by IP address. These allow for ongoing hardware maintenance, which is very useful in larger networks.

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