DNS is useful for much more than name-to-address lookups. It can also be used for routing mail through a domain, or for viewing host-specific information such as the hardware and software in use on a system, or for locating the person responsible for managing that host.
These different pieces of information are stored in the DNS server along with the host's record. The different types of information are reflected in standardized data types called "resource records." Each system in a DNS database can have multiple resource records, allowing the administrator to store an IP address, a comment, and any other data that is offered through standard resource records.
The most common resource records are shown in Figure C.6 below:
Record | Type | Comment |
|---|---|---|
A | Address | IP address for this host |
MX | Mail Exchange | Where to route mail |
TXT | Text | Textual comment |
CNAME | Canonical Name | Alias hostname |
Since a wide variety of DNS servers run on an equally wide variety of platforms, it is impossible to describe how to add these various resource records to your DNS server with any measure of accuracy. However, each of these records do have standard attributes which can be discussed. Refer to the documentation that came with your DNS server for more information about how these records are implemented on your system.
Each entry in a DNS server usually starts with a hostname, followed by the "IN" class field, the resource record (such as A or MX), and the data that is specific to that resource record. For example, the A resource record provides an IP address, while the TXT resource record contains free-flowing text.
All of the entries in the database are assumed to be a part of a single domain (ie, UNOVERICA.COM). If your DNS server services multiple domains, then there should be separate databases for each domain, with unique records for the hosts in those domains.
For more information about the Address record, refer to section C.3.2.1 "A" Records. For more information about the Mail Exchange record, refer to section C.3.2.2 "MX" Records. For more information about the Text record, refer to section C.3.2.3 "TXT" Records. For more information about the Alias record, refer to section C.3.2.4 "CNAME" Records. For more information about DNS' architecture, refer to section C.3.1 DNS' Hierarchy.
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