named.conf.4 (2010 09)

n
named.conf(4) named.conf(4)
(BIND 9.3)
retry A 32-bit integer time to wait in seconds before retrying a failed refresh. See the Time
Specification section for more detail.
expire A 32-bit integer time interval in seconds after which the zone is no longer authoritative.
See the Time Specification section for more detail.
minimum The TTL in seconds for resolvers that cache negative responses. See the Time to Live
(TTL) and Time Specification sections for more detail.
The
SOA specifies a serial number, which should be changed each time the zone file is changed. Note that
it is not advisable to give the serial number as a dotted number, since the translation to normal integers
is via concatenation rather than multiplication and addition. You can represent the year, month, day of
month, and a 0..99 version number (yyyymmddvv) and still fit inside the unsigned 32-bit size of this field.
(It’s true that we will have to rethink this strategy in the year 4294.)
Secondary servers check the serial number at intervals specified by the refresh time in seconds; if the
serial number changes, a zone transfer will be done to load the new data. If a master server cannot be
contacted when a refresh is due, the retry time specifies the interval at which refreshes should be
attempted. If a master server cannot be contacted within the interval given by the expire time, all data
from the zone is discarded by secondary servers.
Example
@ IN SOA ucbvax.Berkeley.EDU. Jane\.Doe.ucbvax.Berkeley.EDU. (
1989020501 ; serial
10800 ; refresh
3600 ; retry
3600000 ; expire
86400 ) ; minimum
Time to Live (TTL)
The TTL field of an RR is a 32-bit integer representing time in seconds. It is primarily used by resolvers
when they cache RRs. The TTL describes how long a RR can be cached before it should be discarded.
This limit does not apply to authoritative data in zones; it is also timed out, but by the refreshing policies
for the zone. The TTL is assigned by the administrator for the zone where the data originates.
While short TTLs can be used to minimize caching, and a zero TTL prohibits caching, the realities of
Internet performance suggest that these times should be on the order of days for the typical host. If a
change can be anticipated, the TTL can be reduced prior to the change to minimize inconsistency during
the change, and then increased back to its former value following the change.
The following three types of TTL are currently used in a zone file.
SOA The minimum field in an SOA RR is the negative-caching TTL. This controls how long
other servers will cache no-such-domain
(NXDOMAIN) responses from you. The max-
imum time for negative caching is 3 hours (
3h).
Note: This use of the minimum field was implemented in RFC 2308, largely superseding
the usage specified in RFC 1034 (but see the default calculation for the ttl field below).
$TTL A $TTL directive at the top of the zone file (before the SOA) provides a default TTL for
subsequent RRs.
Note: The
$TTL directive, defined in RFC 2308, supersedes the original use of the SOA
minimum field specified in RFC 1034.
ttl The ttl field in an RR specifies the TTL for the record. If it is omitted, the value specified
by the previous
$TTL directive is used. If there is no previous $TTL directive, the
minimum field in the SOA resource record is used.
Time Specification
All the TTLs and and the
SOA time fields are specified in seconds, as a 32-bit integer value in the range 0
to 2147483647 (2ˆ31-1).
HP-UX 11i Version 3: September 2010 − 35 − Hewlett-Packard Company 35