C.3.2.1 "A" Records

The A resource record is one of the most important record types, since it provides the IP address of the host being looked-up. Each host should have an A record unless it is an alias for another host (using the CNAME resource record, as described in section C.3.2.4 "CNAME" Records).

It is possible for a host to have multiple A resource records. This is common on routers and other devices with multiple network interfaces and IP addresses.

DNS servers based on the Berkeley Internet Name Daemon (BIND) use the format shown in Figure C.7 for the A resource record:

 Greywolf  IN  A  192.168.1.20

Figure C.7 Sample "A" record.

Since this entry applies to the UNOVERICA.COM domain, a DNS client issuing a query for the IP address of "Greywolf.UNOVERICA.COM" would receive the IP address of 192.168.1.20 in return. If "Greywolf" had multiple IP addresses, then the entry might look like the one shown in Figure C.8 below:

 Greywolf  IN  A  192.168.1.20
           IN  A  192.168.1.21

Figure C.8 Complex "A" record for a host with multiple IP addresses.

Because the A records are both under the "Greywolf" host, they are both associated with that entry, and are read and returned in sequence.

Although it is possible to assign an A resource record to a domain, Unoverica Corporation highly recommends that this strategy be avoided.

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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