IXFR
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Incremental transfer (IXFR) as proposed is a more efficient
mechanism, as it transfers only the changed portion(s) of a zone.
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... name server which requests IXFR is
called an IXFR client and a primary or secondary name server which
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... client and a primary or secondary name server which
responds to the request is called an IXFR server.
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... thinks it needs new information about the zone (typically through SOA
refresh timeout or the NOTIFY mechanism), it sends an IXFR message
containing the SOA serial number of its, presumably outdated, copy of
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An IXFR server should keep record of the newest version of the zone
and the differences between that copy and several older versions ...
... and the differences between that copy and several older versions.
When an IXFR request with an older version number is received, the
IXFR ...
... IXFR request with an older version number is received, the
IXFR server needs to send only the differences required to make that
version current. Alternatively, the server may choose to transfer
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... When a zone has been updated, it should be saved in stable storage
before the new version is used to respond to IXFR (or AXFR) queries.
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... query
is via UDP, the IXFR server may attempt to reply using UDP if the
entire response can be contained in a single DNS packet ...
... packet format is the same as that of a normal DNS
query, but with the query type being IXFR and the authority section
containing the SOA record of client ...
... newest last. Thus, the differential sequences are the history of
changes made since the version known by the IXFR client up to the
server's current version ...
... forever and may delete them anytime. In general, there is a trade-off
between the size of storage space and the possibility of using IXFR.
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... Information about older versions should be purged if the total length
of an IXFR response would be longer than that of an AXFR response.
Given that the purpose of IXFR ...
... IXFR response would be longer than that of an AXFR response.
Given that the purpose of IXFR is to reduce AXFR overhead, this
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An IXFR server may optionally condense multiple difference sequences
into a single difference sequence, thus, dropping information on
intermediate versions ...
... IXFR client has access
to two IXFR servers: A and B, with inconsistent condensation results.
The current version of the IXFR ...
... IXFR servers: A and B, with inconsistent condensation results.
The current version of the IXFR client, received from server A, may
be unknown to server B. In such a case, server B can not provide
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For interoperability, IXFR servers, including those without the
condensation feature, should not flag an error even if it receives a
client ...
... condensation feature, should not flag an error even if it receives a
client's IXFR request with a unknown version number and should,
instead, attempt to perform a full zone transfer.
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... Question | QNAME=JAIN.AD.JP., QCLASS=IN, QTYPE=IXFR |
+---------------------------------------------------+
Answer | <empty> |
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... Question | QNAME=JAIN.AD.JP., QCLASS=IN, QTYPE=IXFR |
+---------------------------------------------------+
Answer | JAIN.AD ...
... Question | QNAME=JAIN.AD.JP., QCLASS=IN, QTYPE=IXFR |
+---------------------------------------------------+
Answer | JAIN.AD ...
... Question | QNAME=JAIN.AD.JP., QCLASS=IN, QTYPE=IXFR |
+---------------------------------------------------+
Answer | JAIN.AD ...
... Question | QNAME=JAIN.AD.JP., QCLASS=IN, QTYPE=IXFR |
+---------------------------------------------------+
Answer | JAIN.AD ...
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The original idea of IXFR was conceived by Anant Kumar, Steve Hotz
and Jon Postel.
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