FORMERR - automatically retried?

[John Horne]

On Tue, 2023-08-15 at 14:28 +0200, George (Yorgos) Thessalonikefs via Unbound-
users wrote:
>
> For upstream traffic, on FORMERR responses, Unbound will retry without
> EDNS if an EDNS query was previously sent.
>
Okay, thanks for clarifying that.

> But from your log output these queries and replies seem to be for the
> downstream (client facing) traffic.
>
...
>
> Then what you see is Unbound receiving a query from 10.121.16.73 for
> collector.newrelic.com. A IN and sending back a FORMERR reply. This
> FORMERR reply came from Unbound itself indicating that there is
> something wrong with the query.
> There is nothing to retry in this case, the client needs to send a
> correct DNS query.
>
Thanks for the reply. You are, of course, correct :-) It just took me a while
to realise the same thing - the client query was causing the problem! :-)

The client is on a server in Azure. For some reason the server was created with
'Accelerated Networking' (?) enabled. This has the effect of creating two
interfaces on the server. We have no other servers with this enabled, and they
have no DNS problems (even with the newrelic site).

Running a simple tcpdump on the client server shows that occasionally a corrupt
packet gets sent to the Unbound resolver. I have no idea why.

I have asked that the Accelerated Networking is disabled on the server in order
to see if that resolves the problem.


Thanks,

John.

>
> On 12/08/2023 20:09, John Horne via Unbound-users wrote:
> > Hello,
> >
> > We are running Unbound 1.16 on a Rocky 9 Linux server, and I'm trying to
> > see
> > why some DNS lookups are intermittently failing. It seems to be that the
> > FORMERR code is being returned, probably due to EDNS being specified.
> >
> > My question is does Unbound disable EDNS and retry requests which return a
> > FORMERR error? I gather that this is done by some DNS software, but am
> > unsure
> > if Unbound does this.
> >
> > Looking at the Unbound logs shows (for example):
> >
> > Aug 11 22:31:35 unbound[944:0] query: 10.121.16.73 collector.newrelic.com.
> > A IN
> > Aug 11 22:31:35 unbound[944:0] reply: 10.121.16.73 - - - FORMERR - - -
> >
> > There is no logged retry for the request, so I am assuming that Unbound
> > does
> > not retry requests after a FORMERR error.
> >
> >
> >
> > Thanks,
> >
> > John.
> >
> > --
> > John Horne | Senior Operations Analyst | Technology and Information
> > Services
> > University of Plymouth | Drake Circus | Plymouth | Devon | PL4 8AA | UK
> > ________________________________
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--
John Horne | Senior Operations Analyst | Technology and Information Services
University of Plymouth | Drake Circus | Plymouth | Devon | PL4 8AA | UK
________________________________
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This email and any files with it are confidential and intended solely for the use of the recipient to whom it is addressed. If you are not the intended recipient then copying, distribution or other use of the information contained is strictly prohibited and you should not rely on it. If you have received this email in error please let the sender know immediately and delete it from your system(s). Internet emails are not necessarily secure. While we take every care, University of Plymouth accepts no responsibility for viruses and it is your responsibility to scan emails and their attachments. University of Plymouth does not accept responsibility for any changes made after it was sent. Nothing in this email or its attachments constitutes an order for goods or services unless accompanied by an official order form.