Efficiency, Reliability and Other Name Resolution Issues and Features
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The main concern with name resolution after efficiency is reliability. As I said earlier in the section, having a name system isn't strictly necessary for the computers, but it's very important for the users, especially on a large network like the Internet. While having a single central place that maintains all information about a name system may make administration simpler, it creates a dangerous single point of failure. If anything happens to the device storing the information, the entire name system fails.
Modern name systems employ redundancies to prevent having the entire system rely on any particular device for resolution. A typical approach in a client/server system is to have multiple servers in different locations (or attached to different networks) that can respond to name resolution requests.
An optional feature in some name resolution systems is load balancing. When properly implemented, load balancing allows a single name to map to more than one underlying address. This allows requests sent to a particular virtual device to actually be directed to a number of different actual physical devices, spreading the load over multiple machines. A common use of this feature is for very popular, heavily-trafficked Web sites.
Finally, while name resolution is obviously designed to allow names to be mapped into addresses, there are cases where we may wish to go in the other direction: given a numeric address, find the name that goes with it. This process, called reverse resolution, is analogous to having a phone number and trying to find the name of the person or company to which it belongs. Just as we can't easily find the name matching a phone number using a conventional phone book (we'd have to scan every page looking for the number), reverse resolution requires special support on the part of the name system. This is especially true if the name system data is distributed over many servers.
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