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DNS7.4 is a name resolution service that translates domain names into IP addresses and vice-versa, and it is implemented in IPBrick by the software Bind using port 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 like HP-UX, for example, 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 different types of servers that:
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.
So we can have master DNS servers, also called primary, and slave DNS servers that can be named as secondary too. Regardless of being master or slave in a zone, a server can have different purposes:
internal DNS server: A internal DNS server (master or slave) serves private domains and resolve names at private IP's. They stay inside the LAN and normally the service is running at the same server that is PDC. Example: pc01.domain.com -> 192.168.0.25. At IPBrick context, it will be a IPBrick.I;
public DNS server: A public DNS (master or slave) serves only public domains and resolve names at public IP's that are well known at the Internet. They can stay at company's network DMZ, but usually the public DNS server of a domain is managed by the company ISP or some hosting company in Internet. Example: www.ipbrick.com -> 80.251.163.69. At IPBrick context, a IPBrick.G/KAV/GT can be as public DNS server of some domain. It's not a good policy to have a unique server managing the same domain with internal records and public records.
The DNS server also 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.