TTL
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... TTL ...
... resolvers when they cache RRs. The TTL describes how
long a RR can be cached before it should be discarded. ...
... RR parts are the fixed header (type, class, TTL) which is consistent for
all RRs, and a variable part (RDATA ...
... cache. 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 ...
... 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 ...
... 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.
...
... . 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 ...
... always last. The IN class and TTL values are often omitted from examples
in the interests of clarity.
...
...
Inverse queries may not return the proper TTL, and do not indicate cases
where the identified RR is one of a set (for example, one address ...
... service which allows name servers to
distribute, and resolvers to cache, negative results with TTLs. For
example, a name server can distribute a TTL ...
... TTLs. For
example, a name server can distribute a TTL along with a name error
indication, and a resolver receiving ...
... indication, and a resolver receiving such information is allowed to
assume that the name does not exist during the TTL period without
consulting authoritative data. Similarly, a resolver can make a query
...
... The idea is that if cached data is known to come from a particular zone,
and if an authoritative copy of the zone's SOA is obtained, and if the
zone's SERIAL has not changed since the data was cached, then the TTL of
the cached data can be reset to the zone MINIMUM value if it is smaller.
This usage is mentioned for planning purposes only, and is not
...
... host's, and returns all
RR content (e.g., TTL) instead of a processed form with local
quoting conventions.
...
... responses. Since resolvers are responsible for
discarding old RRs whose TTL has expired, most
implementations convert the interval specified in
arriving RRs ...
... RR
is stored in the cache. Instead of counting the TTLs
down individually, the resolver just ignores or discards
old RRs ...
... name error. The data is passed back
to the user and entered in the cache for future use if its TTL is
greater than zero.
...
... . When a name server loads a zone, it
forces the TTL of all authoritative RRs to be at least the MINIMUM field
of the SOA, here 86400 seconds, or one day. The NS ...
... host addresses, are not part of the authoritative data in
the zone, and hence have explicit TTLs.
...
... NIC.ARPA. A key item in the SOA is the 86400
second minimum TTL, which means that all authoritative data in the zone
has at least that TTL, although higher values may be explicitly
...
... second minimum TTL, which means that all authoritative data in the zone
has at least that TTL, although higher values may be explicitly
specified.
...
... header
does not have AA set, and the TTLs are different. The inference is that
the data did not come from a zone, but from a cache. The difference
...
... the data did not come from a zone, but from a cache. The difference
between the authoritative TTL and the TTL here is due to aging of the
data in a cache ...
... cache. The difference
between the authoritative TTL and the TTL here is due to aging of the
data in a cache. The difference in ordering of the RRs ...
... Neither of these answers have AA set, so neither response comes from
authoritative data. The different contents and different TTLs suggest
that the two servers cached data at different times, and that the first
server cached the response to a QTYPE=A query ...