[Pdns-users] PowerDNS authoritative server UDP port?

[Brian Candler]

On 30/10/2019 02:33, Aaron D. Gifford wrote:
> On a FreeBSD system running PowerDNS authoritative server 4.2.0, I 
> noticed this:
>
> # sockstat -4
> USER     COMMAND    PID   FD PROTO  LOCAL ADDRESS FOREIGN ADDRESS
> root     pdns_serve 40055 4  udp4 192.168.50.12:53 
> <http://192.168.50.12:53>     *:*
> root     pdns_serve 40055 6  tcp4 192.168.50.12:53 
> <http://192.168.50.12:53>     *:*
> root     pdns_serve 40055 8  tcp4 192.168.50.12:55401 
> <http://192.168.50.12:55401> 127.0.0.1:3306 <http://127.0.0.1:3306>
> root     pdns_serve 40055 9  tcp4 192.168.50.12:54277 
> <http://192.168.50.12:54277> 127.0.0.1:3306 <http://127.0.0.1:3306>
> root     pdns_serve 40055 16 udp4 192.168.50.12:19413 
> <http://192.168.50.12:19413>  *:*
> ...
>
> Why is it listening on UDP port 19413?  I thought I'd disabled various 
> subsystems that might want to listen on a TCP or UDP port.

If you restart pdns I think you'll find it binds to a different random 
port, which almost certainly means it's a socket which has been created 
for the purpose of sending *outbound* UDP packets.  I see the same here:

$ sudo netstat -naup | grep pdns
udp        0      0 0.0.0.0:53 0.0.0.0:*                           
17497/pdns_server
udp        0      0 0.0.0.0:12579 0.0.0.0:*                           
17497/pdns_server
udp6       0      0 :::53 :::*                                
17497/pdns_server
udp6       0      0 :::11846 :::*                                
17497/pdns_server

$ sudo systemctl restart pdns

$ sudo netstat -naup | grep pdns
udp        0      0 0.0.0.0:53 0.0.0.0:*                           
12560/pdns_server
udp        0      0 0.0.0.0:17662 0.0.0.0:*                           
12560/pdns_server
udp6       0      0 :::53 :::*                                
12560/pdns_server
udp6       0      0 :::16544 :::*                                
12560/pdns_server

Although pdns auth no longer has a recursor option, and I have 
expand-alias turned off, I suspect it is for sending NOTIFY packets.

Anyway, it's not a listening port, so you don't need to worry about it.

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