Bind 9 Administrator Reference Manual

Chapter 6. BIND 9 Configuration Reference
set of resource information associated with a particular name is composed of separate RRs. The order of
RRs in a set is not significant and need not be preserved by nameservers, resolvers, or other parts of the
DNS. However, sorting of multiple RRs is permitted for optimization purposes, for example, to specify
that a particular nearby server be tried first. See Section 6.2.14.11 and Section 6.2.14.12.
The components of a Resource Record are:
owner name the domain name where the RR is found.
type an encoded 16 bit value that specifies the type of the
resource in this resource record. Types refer to abstract
resources.
TTL the time to live of the RR. This field is a 32 bit integer in
units of seconds, and is primarily used by resolvers when they
cache RRs. The TTL describes how long a RR can be cached
before it should be discarded.
class an encoded 16 bit value that identifies a protocol family or
instance of a protocol.
RDATA the type and sometimes class-dependent data that describes
the resource.
The following are types of valid RRs (some of these listed, although not obsolete, are experimental (x) or
historical (h) and no longer in general use):
A a host address.
A6 an IPv6 address.
AAAA Obsolete format of IPv6 address
AFSDB (x) location of AFS database servers. Experimental.
CERT holds a digital certificate.
CNAME identifies the canonical name of an alias.
DNAME for delegation of reverse addresses. Replaces the domain name
specified with another name to be looked up. Described in RFC
2672.
GPOS Specifies the global position. Superseded by LOC.
HINFO identifies the CPU and OS used by a host.
ISDN (x) representation of ISDN addresses. Experimental.
KEY stores a public key associated with a DNS name.
KX identifies a key exchanger for this DNS name.
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