It is the idea of caching, but not beyond the record TTL surely? And why stop only when I reset another piece of software (whether I do that after 5 minutes or 4 hours).
I'm finding that the upstream server is inconsistent in how much information it returns - just occasionally not returning anything beyond the first CNAME - which means that this is probably passed on to my program as such, which means that something else is involved in triggering it... I don't expect this to be easy :( I think we may have found the application bug (it just doesn't know how to handle a non IP address return), but I'd still like to understand the behaviour from dnsmasq. On Wed, 20 Mar 2019 at 23:30, Geert Stappers <stapp...@stappers.nl> wrote: > On Wed, Mar 20, 2019 at 09:00:20PM +0000, John Robson wrote: > > Hi, > > > > I have a library which I think has a bug, but this bug is affecting DNS > > queries, and bringing out some odd behaviour in dnsmasq... > > > > Program is making a query to resolve an address (foo.bar.com) > > A normal query results in a CNAME (foo.bar.com.edgekey.net), which > results > > in another CNAME (e1234.a.akamaiedge.net) which has an A record. > > > > However every so often dnsmasq returns just the first CNAME. > > Note I haven't yet caught it in the act of that first truncated response. > > The only thing that makes sense to me is if the edgekey.net name servers > > didn't respond in good time... but.... > > > > However the bug in the library then means it asks again, instantly. and > > again... and again.... > > It manages over 100MB/ minute of DNS requests - dnsmasq answering them > all > > from the cache (I see *no* external requests for that address). > > Hey, that is the idea about DNS caching ... > > > > When I restart the program the very first query (identical query as > before) > > gets a complete answer from dnsmasq. > > > > What I can't understand is how that restart makes any difference to > dnsmasq. > > Does dnsmasq have some sort of 'Oh hell the query load is insane I'm just > > extending the cache a bit to help' mode which it then escapes from as the > > program restarts? > > There are no external queries for this name during the period of > insanity, > > but the first request after does get put to the external name servers. > > > > I'm running an 'external interface only' capture to try and capture the > > initial error condition (which I very much doubt is a problem in > dnsmasq), > > to see if that can shed some light on the issue. > > > > > > Thoughts? debug hints? laughter? > > > To me it seems that the first DNS request from the application has > "recursion". Upon encountering the bug is doing the app "non > recursion". With "recusion" do I mean 'When the reply is not an A-record > do a next query'. > > On debug hints: Currently is the suspected trigger of the bug > a DNS that doesn't respond within good time. So make a "chain" > of DNServers where you control the response time of one. > > Good luck with it. And feel welcome to report back. > > > > Cheers, > > John > > Groeten > Geert Stappers > -- > Leven en laten leven > > _______________________________________________ > Dnsmasq-discuss mailing list > Dnsmasqemail@example.com > http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss > -- *John Robson*
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