Score:0

IXFR and inconsistent condensation results

br flag

https://www.rfc-editor.org/rfc/pdfrfc/rfc1995.txt.pdf says:

An IXFR server may optionally condense multiple difference sequences into a single difference sequence, thus, dropping information on intermediate versions.

This may be beneficial if a lot of versions, not all of which are useful, are generated. (...).

But, this feature may not be so useful if an IXFR client has access to two 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 incremental data from the unknown version and a full zone transfer is necessary.

Could you shed some more light on how such a situation could occur? I mean, how is it even possible that an IXFR client would do IXFRs from two servers as it is primarily - as I understand - used to transfer the "lacking part" of the zone from master authoritative server.

Also, even if the IXFR client sends for some reason IXFRs to two different server, I still don't understand what the problem is about. Can you give some illustrative example?

Score:0
cn flag

I cannot say for sure what scenario was imagined by the author, but this is my take on it:

Nameserver A has the actual master zone
Nameserver B itself gets the zone via IXFR from A
(One of several options, another would be that A and B both IXFR from C which has the actual master zone.)

Your nameserver is configured to IXFR the zone from A or B

By the same reasoning of how multiple changes can be condensed into one transfer via IXFR, B may not have every single intermediate version available.

If you then IXFR from B, but your current version was received from A, you may currently be at a version that B never saw and B would fall back to full AXFR.

mangohost

Post an answer

Most people don’t grasp that asking a lot of questions unlocks learning and improves interpersonal bonding. In Alison’s studies, for example, though people could accurately recall how many questions had been asked in their conversations, they didn’t intuit the link between questions and liking. Across four studies, in which participants were engaged in conversations themselves or read transcripts of others’ conversations, people tended not to realize that question asking would influence—or had influenced—the level of amity between the conversationalists.