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

[Bernardo]

Hi all,

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 192.168.10.100;
notify-source 192.168.10.100 port 53;
transfer-source 192.168.10.100 port 53;

This problem causes other major problems with BIND (notify messages get
lost, zone changes propagation takes longer, dynamic updates get lost,
etc...)

Other related posts at bind-users at lists.isc.org:
- See my post ( BIND ignores "packets received correctly" ) from January
2020
- Look also the post ( No response from localhost with "allow-query { any;
};"  ) from September 2020

Notes for BIND 9.16.1
Known Issues
UDP network ports used for listening can no longer simultaneously be used
for sending traffic. An example configuration which triggers this issue
would be one which uses the same address:port pair for listen-on(-v6)
statements as for notify-source(-v6) or transfer-source(-v6). While this
issue affects all operating systems, it only triggers log messages (e.g.
“unable to create dispatch for reserved port”) on some of them. There are
currently no plans to make such a combination of settings work again.

Hope this helps someone else to avoid loosing a lot of time.

Regards,

-- 
Bernardo

El sáb, 23 ene 2021 a las 11:35, Bernardo (<bernardo.pons at gmail.com>)
escribió:

> Hi all,
>
> Is it normal to see bind listening on UDP port 53 using 2 fd?
>
> udp     UNCONN   0        0          192.168.10.100:53            0.0.0.0:*
>      users:(("named",pid=4205,fd=512))
> udp     UNCONN   0        0          192.168.10.100:53            0.0.0.0:*
>      users:(("named",pid=4205,fd=15))
> tcp     LISTEN   0        10         192.168.10.100:53            0.0.0.0:*
>      users:(("named",pid=4205,fd=17))
> tcp     LISTEN   0        128             127.0.0.1:953           0.0.0.0:*
>      users:(("named",pid=4205,fd=21))
>
> Does this make any sense?
>
> According to "rndc status" command "UDP listeners per interface: 1"
>
> # rndc status
> version: BIND 9.16.6 (Stable Release) <id:25846cf>
> running on ns2: Linux x86_64 5.3.18-lp152.60-default #1 SMP Tue Jan 12
> 23:10:31 UTC 2021 (9898712)
> boot time: Sat, 23 Jan 2021 10:14:09 GMT
> last configured: Sat, 23 Jan 2021 10:14:09 GMT
> configuration file: /etc/named.conf (/var/lib/named/etc/named.conf)
> CPUs found: 1
> worker threads: 1
> UDP listeners per interface: 1
> number of zones: 156 (0 automatic)
> debug level: 0
> xfers running: 0
> xfers deferred: 0
> soa queries in progress: 0
> query logging is ON
> recursive clients: 0/900/1000
> tcp clients: 0/150
> TCP high-water: 1
> server is up and running
>
>
>
> --
> Bernardo
>
>
>
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-- 
Bernardo
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