Bind 9 Administrator Reference Manual

Chapter 6. BIND 9 Configuration Reference
Following the owner, we list the TTL, type, and class of the RR. Class and type use the mnemonics
defined above, and TTL is an integer before the type field. In order to avoid ambiguity in parsing, type
and class mnemonics are disjoint, TTLs are integers, and the type mnemonic is always last. The IN class
and TTL values are often omitted from examples in the interests of clarity.
The resource data or RDATA section of the RR are given using knowledge of the typical representation
for the data.
For example, we might show the RRs carried in a message as:
ISI.EDU. MX 10 VENERA.ISI.EDU.
MX 10 VAXA.ISI.EDU
VENERA.ISI.EDU A 128.9.0.32
A 10.1.0.52
VAXA.ISI.EDU A 10.2.0.27
A 128.9.0.33
The MX RRs have an RDATA section which consists of a 16 bit number followed by a domain name.
The address RRs use a standard IP address format to contain a 32 bit internet address.
This example shows six RRs, with two RRs at each of three domain names.
Similarly we might see:
XX.LCS.MIT.EDU. IN A 10.0.0.44
CH A MIT.EDU. 2420
This example shows two addresses for XX.LCS.MIT.EDU, each of a different class.
6.3.2. Discussion of MX Records
As described above, domain servers store information as a series of resource records, each of which
contains a particular piece of information about a given domain name (which is usually, but not always, a
host). The simplest way to think of a RR is as a typed pair of data, a domain name matched with a
relevant datum, and stored with some additional type information to help systems determine when the
RR is relevant.
MX records are used to control delivery of email. The data specified in the record is a priority and a
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