Comment 19 for bug 1003842
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| Sergio Callegari (callegar) wrote Re: [Bug 1003842] Re: Precise NM with "dns=dnsmasq" breaks systems with non-equivalent upstream nameservers | #19 |
My idea for a heuristic was indeed extremely simple. In case the first name server has a non public ip address, auto switch to strict order.
Il giorno 27/mag/2012, alle ore 23:04, Simon Kelley <email address hidden> ha scritto:
> 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.
>
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> Title:
> Precise NM with "dns=dnsmasq" breaks systems with non-equivalent
> upstream nameservers
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