Comment 18 for bug 1003842
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| Simon Kelley (simon-thekelleys) wrote Re: Precise NM with "dns=dnsmasq" breaks systems with non-equivalent upstream nameservers | #18 |
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f33e652
(Get the code!)
Thomas in #17
A heuristic for this is difficult, because you have to prove a negative. If we can assume the first nameserver has local addresses, we can never return a reply from any other nameserver until we have the reply from the first one, in case the first one has different data. Once we see different data from different nameservers, we can go to --strict-order mode, but the opposite is not true: the same answer for a particular query doesn't guarantee that the answers to future queries will always agree. There's no way to be sure that the nameservers are equivalent based on the history of returned queries. Unless we can assume that, we always need to wait for the first nameserver to reply (or a timeout) and have to stay in --strict-order mode forever.
There is one possibility, which is to assume that nameservers are equivalent, but switch to --strict-order mode if conflicting replies are seen. When a query is forwarded to all available servers, and the first reply sent back to the original requestor, keep the record of the reply (at least, a bit indicating NODATA/NXDOMAIN or a valid reply. If another reply comes in later from another nameserver which conflicts, then switch to --strict-order mode. This will not get the first queries right, but it will be triggered eventually (and it might be triggered, swicthing mode forever, by random server glitches)
For a single-host cache, --strict-order might be the simplest fix......
Simon.