Re: [exim] DNS problems with sending via multiple smarthosts

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Author: Jeremy Harris
To: exim-users
Subject: Re: [exim] DNS problems with sending via multiple smarthosts
On 18/07/2019 23:08, Evgeniy Berdnikov via Exim-users wrote:
> Quite puzzling... The only difference I see here is the presence of one
> authority record in dns query from Exim, marked as [1au].
> Tcpdump man page states:
>        A few anomalies are checked and may result in extra fields enclosed  in
>        square  brackets:   If a query contains an answer, authority records or
>        additional records section, ancount, nscount, or arcount are printed as
>        `[na]', `[nn]' or  `[nau]' where n is the appropriate count.

> Running tcpdump with -vvv shows that there is an authority record for root.
> I don't know is this behaviour legal or not, and why this record is present
> in exim queries. But I propose to try two other methods to resolve name:
> 1: exim4 -be '${lookup dnsdb{}{$value}fail}'
> 2: perl -e '($n,$a,$t,$l,@ip)=gethostbyname(""); print "n=$n\na=$a\n"; for (@ip) {($w,$x,$y,$z)=unpack('W4',$_); print "$w.$x.$y.$z\n"}'
> In my experiments 1st variant results in additional authority record, the
> 2nd does not (as manual run of telnet). Does 1st variant fail when exim
> fails to run transport?

Might there be a dnssec-related difference? Would that show in the
text tcpdump output, or would you need to look carefully with wireshark?