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DNS7.4 is a name resolution service in IP addresses and vice-versa, and it is implemented in IPBrick by the software Bind using door 53 UDP/TCP. The majority of queries consists of a simple UDP request by the client, followed by a UDP answer of the server. There are two situations where the TCP is used: when the data to be sent by the user exceed 512 bytes or at the transference of zones. Some operating systems (HP-UX, for ex:), even adopt DNS implementations always using TCP, thus increasing reliability. The service acts like a database with information about the connections of a IP network, and that information is organized into domains. The used notation represents FQDN7.5:
servername.company.region
Being the "servername.company.region" the FQDN, the "company.region" designated as the domain, "company" the sub-domain and "region" the top domain (Top Level Domain), which is administrated by an entity denominated ICANN7.6. A DNS server generates a database about a certain part of the domain, what is normally designated by zone, and there are two types of servers:
master: It obtains the data from a zone which it manages from its own database;
slave: It obtains the data from the primary master, existing one or more in a network. Whenever there are changes in the configuration of the areas served by the master, this server is always notified, proceeding to the update of database.
The DNS server allows the resolution of names in a reverse mode, that is, answer with the name - FQDN from a certain IP address. This device allows the confirmation of the authenticity of an IP address, important aspect in the email service.