RRs are represented in binary form in the packets of the DNS protocol, and are usually represented in highly encoded form when stored in a name server or resolver. In this memo, we adopt a style similar to that used in master files in order to show the contents of RRs. In this format, most RRs are shown on a single line, although continuation lines are possible using parentheses.
The start of the line gives the owner of the RR. If a line begins with a blank, then the owner is assumed to be the same as that of the previous RR. Blank lines are often included for readability.
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.