11.5 DNS Protocol
The DNS protocol works with several types of operations. The most commonly used operation is a DNS QUERY. It is a query that enables the obtaining of one or more records from the DNS database. The DNS QUERY operation was for a long time the only operation possible in the DNS system. New modifications to the DNS protocol have brought new kinds of operations, for example, DNS NOTIFY and DNS UPDATE.
The DNS protocol operates on a query/answer basis. A client sends a query to a server and the server answers it. DNS protocol uses name compression in order to make DNS packets as compact as possible.
The DNS protocol is an application-layer protocol and, as such, it does not carry out packet transfer on its own. The packet transfer is delegated to a transport protocol. Unlike the overwhelming majority of other application protocols, DNS protocol uses both UDP and TCP. Each query and the answer to it are transferred by the same transport protocol.
With translation queries (i.e....
