[SOLVED] Re: bind listening on UDP port 53 using 2 fd

Bernardo bernardo.pons at gmail.com
Mon Jan 25 13:05:52 UTC 2021

Hi Matus,

Yes. This causes serious problems.

The problem is that these perfectly valid configuration lines in
/etc/named.conf file (provided that is the IPv4 address of
your DNS server, it doesn't matter if it is a primary or secondary) will
cause you a lot of trouble.

query-source address;
notify-source port 53;
transfer-source port 53;

These configuration lines will cause you problems as described in my post (
BIND ignores "packets received correctly" ) from January 2020.

It seems that this is a know issue since BIND 9.16.1 version: UDP network
ports used for listening can no longer simultaneously be used for sending

Prior to this BIND version these very same configuration lines worked fine.

As I said, I hope this warning helps someone else to avoid loosing a lot of
time trying to find out what is happening to their DNS servers running BIND


de virus. www.avast.com

El lun, 25 ene 2021 a las 11:13, Matus UHLAR - fantomas (<uhlar at fantomas.sk>)

> On 23.01.21 12:44, Bernardo wrote:
> >Finally I've found the solution.
> >The problem seems to be caused by a known issue since BIND version 9.16.1
> >
> >Commenting out these lines in /etc/named.conf solves the issue:
> >
> >query-source address;
> >notify-source port 53;
> >transfer-source port 53;
> this should not cause a problem and may cause troubles when
> is not the primary address.
> the "port 53" is usually useless (unless you have stateless firewall) and
> may be what caused your problem.
> --
> Matus UHLAR - fantomas, uhlar at fantomas.sk ; http://www.fantomas.sk/
> Warning: I wish NOT to receive e-mail advertising to this address.
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