cache
Click on the red underlined text to get to the source
... Where there tradeoffs between the cost of acquiring data, the
speed of updates, and the accuracy of caches, the source of
the data should control the tradeoff.
...
... domain tree's structure and set information. A name
server may cache structure or set information about any part
of the domain tree ...
... might share a database consisting of the the zones managed by the name
server and the cache managed by the resolver.
...
... bit integer in units of seconds, an is primarily used by
resolvers when they cache RRs. The TTL describes how
...
... TTL field is a time limit on how long an RR can be
kept in a 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 ...
... a network where we want to concentrate the cache rather than
having a separate cache for each client ...
... network where we want to concentrate the cache rather than
having a separate cache for each client.
...
... Start matching down in the cache. If QNAME is found in the
cache, copy all RRs attached to it that match QTYPE into the
answer section. If there was no delegation ...
... answer section. If there was no delegation from
authoritative data, look for the best one from the cache, and
put it in the authority section. Go to step 6.
...
... DNS provides an optional service which allows name servers to
distribute, and resolvers to cache, negative results with TTLs. For
example, a name server ...
... consulting authoritative data. Similarly, a resolver can make a query
with a QTYPE which matches multiple types, and cache the fact that some
of the types are not present.
...
... not required to add the SOA RRs in all authoritative responses, nor are
resolvers required to cache negative results. Both are recommended.
All resolvers and recursive name servers are required to at least be
able to ignore the SOA RR ...
... other hosts. Because a resolver may need to consult several name
servers, or may have the requested information in a local cache, the
amount of time that a resolver will take to complete can vary quite a
bit, from milliseconds to several seconds.
...
... A very important goal of the resolver is to eliminate network delay and
name server load from most requests by answering them from its cache of
prior results. It follows that caches which are shared by multiple
...
... name server load from most requests by answering them from its cache of
prior results. It follows that caches which are shared by multiple
processes, users, machines, etc., are more efficient than non-shared
caches.
...
... prior results. It follows that caches which are shared by multiple
processes, users, machines, etc., are more efficient than non-shared
caches.
...
... service in a PC which lacks the resources to perform the resolver
function, or can centralize the cache for a whole local network or
organization.
...
... careful to never let cached information override zone data. In this
discussion the term "local information" is meant to mean the union of
the cache and such shared zones, with the understanding that
authoritative data is always used in preference to cached data when both
are present.
...
... CACHE ...
... RRs to some sort of absolute time when the RR
is stored in the cache. Instead of counting the TTLs
down individually, the resolver just ignores or discards
...
...
a. if the response answers the question or contains a name
error, cache the data as well as returning it back to
the client.
...
... b. if the response contains a better delegation to other
servers, cache the delegation information, and go to
step 2.
...
... c. if the response shows a CNAME and that is not the
answer itself, cache the CNAME, change the SNAME to the
canonical ...
... go back to step 3.
Step 1 searches the cache for the desired data. If the data is in the
cache, it is assumed to be good enough for normal use. Some resolvers
have an option at the ...
...
Step 1 searches the cache for the desired data. If the data is in the
cache, it is assumed to be good enough for normal use. Some resolvers
have an option at the user interface which will force the resolver to
...
... either gives the required data or a 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.
...
... 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
between the authoritative TTL and the TTL ...
... TTL and the TTL here is due to aging of the
data in a cache. The difference in ordering of the RRs in the answer
section is not significant.
...
... query was sent to C.ISI.EDU, its response might be the same
as shown above if it had its own address in its cache, but might also
be:
...
... for its client. We assume that the resolver is starting without a
cache, as might be the case after system boot. We further assume that
the system is not one of the hosts in the data and that the host ...
...
The following examples illustrate the use of a cache, so each example
assumes that previous requests have completed.
...
... cache for MX RRs at ISI.EDU, but the
empty cache wouldn't be helpful. The resolver would recognize that it
needed to query foreign servers and try to determine the best servers to
...
... domains ISI.EDU, EDU,
and the root. These searches of the cache would also fail. As a last
resort, the resolver would use the information from the SBELT, copying
it into its SLIST structure.
...
... closer delegation to ISI.EDU than its existing SLIST (since it matches
three labels). The resolver would then cache the information in this
response and use it to set up a new SLIST:
...
... RRs for
65.0.6.26.IN-ADDR.ARPA. This information is not in the cache, so the
resolver would look for foreign servers to ask. No servers would match,
so it would use SBELT again. (Note that the servers for the ISI.EDU
...
... resolver would look for foreign servers to ask. No servers would match,
so it would use SBELT again. (Note that the servers for the ISI.EDU
domain are in the cache, but ISI.EDU is not an ancestor of
65.0.6.26.IN-ADDR.ARPA, so the SBELT is used.)
...
... find the NS RRs in the cache for ISI.EDU when it looks for foreign
servers to ask. Using this data, it would construct a SLIST of the
form:
...