IPTables rules for DNS

Suppose the default INPUT DROP and a DNS server is installed, now I will give an example of IPTables rules so that clients can access the DNS server.

To open the DNS port in IPTables, let’s execute the rule:

sudo iptables -A INPUT -i eth0 -p udp --dport 53 -m state --state ESTABLISHED -j ACCEPT
sudo iptables -A INPUT -i eth0 -p tcp --dport 53 -m state --state ESTABLISHED -j ACCEPT

Continue reading “IPTables rules for DNS”

Dnstop – monitoring of requests to the DNS server

The utility is installed in Ubuntu/Debian by the command:

sudo apt-get install dnstop

Start-up example:

dnstop -n google.com eth0

I’ll describe the list of possible startup keys:
-4 (number of IPv4 packets)
-6 (number of IPv6 packets)
-Q (number of requests)
-R (number of answers)
-a (anonymous IP addresses)
-i ADDRESS (ignoring the specified IP address)
-n NAME (number of requests for the specified address only)
-l NUMBER (monitoring up to the specified number of requests)
-f (filter name)

How to convert a list of IP addresses to DNS names

In Linux, you can convert a list of IP addresses into DNS names, for example, by a simple script.

To do this, create an empty file with the extension .sh, make it executable and add the content to it:

while read ip traf ; do
    name=`host $ip|awk '{print $NF}'`
    echo -e "$name\t$ip\t$traf"
done >name_ip_traf.lst <ip_traf.lst

Where ip_traf.lst is a file with a list of IP addresses that need to be converted to DNS names.

You can make it executable by the command:

chmod +rwx file.sh

Run the script in the directory where it is located by the command:


Or run by specifying the full path:


After the startup, you must wait for a while or interrupt the execution by pressing CTRL+C.

Configuring Cloud in Mikrotik

Starting from the version of RouterOS v6.14, the Cloud function is added which allows using the Dynamic DNS name for a device that is automatically assigned and can be accessed by it even if the IP address is changed.

Example of switching through the console:

ip cloud set enabled=yes

Example of viewing parameters:

ip cloud print

Enable device time update with DDNS server time (if SNTP or NTP service is not configured):

ip cloud update-time yes/no

Immediate update of DDNS:

ip cloud force-update

View the DDNS name:

ip cloud dns-name

View the public IP address to which DDNS is bound:

ip cloud public-address

Binding DDNS to a local IP address instead of a public one, for example to, etc.)

ip cloud advanced use-local-address yes/no

View the current status of the Cloud (updated, updated, error, etc.):

ip cloud status

Through the graphical interface of the Cloud settings can be found in the menu “IP” – “Cloud”.