This issue is reproducible on RH-7.x, RH-8.x and RH-9.x

By default dnsmasq allow only a single instance to bind tcp/udp port 53 to single instance but with bind-dynamic it allows more and more.

Note: in RH-9 you have to disable bind-interface in dnsmasq.conf.

Reprocer steps:

*** Without bind-dynamic ***

[root@192 ~]# grep bind /etc/dnsmasq.d/a.conf 
#bind-dynamic
[root@192 ~]# 
[root@192 ~]# systemctl restart dnsmasq
[root@192 ~]# 
[root@192 ~]# ps -ef | grep dnsmasq
dnsmasq     2782       1  0 07:51 ?        00:00:00 /usr/sbin/dnsmasq
root        2784    2515  0 07:51 pts/1    00:00:00 grep --color=auto dnsmasq
[root@192 ~]# 

1. netstat -neopa | grep dnsmasq | grep -w udp
   udp        0      0 127.0.0.1:53            0.0.0.0:*                           0          29667      2834/dnsmasq         off (0.00/0/0)

[root@192 ~]# dnsmasq -help

dnsmasq: failed to create listening socket for port 53: Address already in use
[root@192 ~]# 

*** with bind-dynamic ***

You can have multiple different services binding the same ip and the same port.

This causes disruption for clients. Like in the case of openshift 3.x (rh-7) where some changes (related to openshift internal domain) are pushed via D-BUS.  SDN pushes changes via dbus to X service but when traffic comes to Y service, it doesn't understand that and forwards the traffic to the forwarder causing internal dns resolution failure.

[root@192 ~]# dnsmasq -help
[root@192 ~]# 
[root@192 ~]# ps -ef | grep dnsmasq
dnsmasq     2834       1  0 07:53 ?        00:00:00 /usr/sbin/dnsmasq
dnsmasq     2847       1  0 07:54 ?        00:00:00 dnsmasq -help
root        2849    2515  0 07:54 pts/1    00:00:00 grep --color=auto dnsmasq
[root@192 ~]# 
[root@192 ~]# netstat -neopa | grep dnsmasq | grep -w udp
udp        0      0 127.0.0.1:53            0.0.0.0:*                           0          29832      2847/dnsmasq         off (0.00/0/0)
udp        0      0 127.0.0.1:53            0.0.0.0:*                           0          29667      2834/dnsmasq         off (0.00/0/0)
[root@192 ~]# 
[root@192 ~]# dnsmasq -help
[root@192 ~]# 
[root@192 ~]# netstat -neopa | grep dnsmasq | grep -w udp
udp        0      0 127.0.0.1:53            0.0.0.0:*                           0          29925      2855/dnsmasq         off (0.00/0/0)
udp        0      0 127.0.0.1:53            0.0.0.0:*                           0          29832      2847/dnsmasq         off (0.00/0/0)
udp        0      0 127.0.0.1:53            0.0.0.0:*                           0          29667      2834/dnsmasq         off (0.00/0/0)
[root@192 ~]# 
[root@192 ~]# dnsmasq -help
[root@192 ~]# 
[root@192 ~]# netstat -neopa | grep dnsmasq | grep -w udp
udp        0      0 127.0.0.1:53            0.0.0.0:*                           0          30000      2861/dnsmasq         off (0.00/0/0)
udp        0      0 127.0.0.1:53            0.0.0.0:*                           0          29925      2855/dnsmasq         off (0.00/0/0)
udp        0      0 127.0.0.1:53            0.0.0.0:*                           0          29832      2847/dnsmasq         off (0.00/0/0)
udp        0      0 127.0.0.1:53            0.0.0.0:*                           0          29667      2834/dnsmasq         off (0.00/0/0)
[root@192 ~]#