TTL
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... the precise definition of the Time to Live (TTL) ...
... DNS server should use when replying to a query,
the issue of differing TTLs for DNS records with the same label,
class ...
... made in this memo. A minor ambiguity in RFC1034 concerned with SOA
records is also corrected, as is one in the definition of the TTL
(Time To Live) and some possible confusion in use of the TC bit ...
... the RRs in an RRSet to have different TTLs. No uses for this have
been found that cannot be better accomplished in other ways. This
can, however, cause partial replies (not marked "truncated") from a
...
... been found that cannot be better accomplished in other ways. This
can, however, cause partial replies (not marked "truncated") from a
caching server, where the TTLs for some but not all the RRs in the
RRSet ...
... RRs from an RRSet with
differing TTLs, it should treat this as an error. If the RRSet
concerned is from a non-authoritative source for this data, the
...
... client should treat the RRs for all purposes as if all TTLs in the
RRSet had been set to the value of the lowest TTL ...
... TTLs in the
RRSet had been set to the value of the lowest TTL in the RRSet. In
no case may a server send an RRSet ...
... RRSet currently in the
cache, as appropriate. Consequently the issue of TTLs varying
between the cache and a response does not cause concern, one will be
...
... identical to that in its cache, with the possible exception of the
TTL value, it may, optionally, update the TTL in its cache ...
... TTL in its cache with the
TTL of the received answer. It should do this if the received answer
would be considered more authoritative (as discussed in the next
section) than the previously cached answer.
...
... RR) be both the first and
last record of the reply. Where duplicates are required this way,
the TTL transmitted in each case must be the same.
...
... 1035std13, which defines
the format of a Resource Record, that the definition of the TTL field
contains a throw away line which states that the TTL of an SOA record
...
... Resource Record, that the definition of the TTL field
contains a throw away line which states that the TTL of an SOA record
should always be sent as zero to prevent caching. This is mentioned
nowhere else, and has not generally been implemented.
...
... should always be sent as zero to prevent caching. This is mentioned
nowhere else, and has not generally been implemented.
Implementations should not assume that SOA records will have a TTL of
zero, nor are they required to send SOA records with a TTL of zero.
...
... Implementations should not assume that SOA records will have a TTL of
zero, nor are they required to send SOA records with a TTL of zero.
...
... Time to Live (TTL) ...
...
The definition of values appropriate to the TTL field in STD 13 is
not as clear as it could be, with respect to how many significant
bits ...
... not as clear as it could be, with respect to how many significant
bits exist, and whether the value is signed or unsigned. It is
hereby specified that a TTL value is an unsigned number, with a
minimum value of 0, and a maximum value of 2147483647. That is, a
maximum of 2^31 - 1. When transmitted, this value shall be encoded
...
... in the less significant 31 bits of the 32 bit TTL field, with the
most significant, or sign, bit set to zero ...
...
Implementations should treat TTL values received with the most
significant bit set as if the entire value received was zero.
...
...
Implementations are always free to place an upper bound on any TTL
received, and treat any larger values as if they were that upper
bound. The TTL ...
... TTL
received, and treat any larger values as if they were that upper
bound. The TTL specifies a maximum time to live, not a mandatory
time to live ...