Resolution

This is an expected behavior, below there are some outputs from netstat filtered by named service and their explanation.

# netstat -lnptu |grep "named\W*$" 

Incoming TCP requests

tcp 0 0 :::53         :::*      LISTEN 1234/named 

Incoming UDP requests to IPv4 192.168.1.20

udp 0 0 192.168.1.20:53    0.0.0.0:*        1234/named

Incoming UDP requests to IPv4 localhost

udp 0 0 127.0.0.1:53  0.0.0.0:*        1234/named

Dynamic chosen port for outgoing queries

udp 0 0 0.0.0.0:32868 0.0.0.0:*        1234/named

Incoming UDP request to any IPv6

udp 0 0 :::53         :::*             1234/named

6.2.16.6 Query Address

If the server doesn’t know the answer to a question, it will query other name servers. query-source specifies the address and port used for such queries. For queries sent over IPv6, there is a separate query-source-v6 option. If address is * (asterisk) or is omitted, a wildcard IP address (INADDR ANY) will be used.

If port is * or is omitted, a random port number from a pre-configured range is picked up and will be used for each query. The port range(s) is that specified in the use-v4-udp-ports (for IPv4) and use-v6-udp-ports (for IPv6) options, excluding the ranges specified in the avoid-v4-udp-ports and avoid-v6-udp-ports options, respectively.

The defaults of the query-source and query-source-v6 options are:

query-source address * port *;
query-source-v6 address * port *;

If use-v4-udp-ports or use-v6-udp-ports is unspecified, named will check if the operating system provides a programming interface to retrieve the system’s default range for ephemeral ports. If such an interface is available, named will use the corresponding system default range; otherwise, it will use its own defaults:

use-v4-udp-ports { range 1024 65535; };
use-v6-udp-ports { range 1024 65535; };

Source: Bind9 ARM (http://www.isc.org/software/bind/documentation/)