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Block Domains Dynamic IP using CSF – Quick fix !

Are you trying to Block Domains Dynamic IP using CSF?

CSF is one of the best security tools that can protect the server from various attacks.

Sometimes there will be certain domains that have dynamic IPs. Thus, we cannot block a particular IP to block the domain on the server.

At Bobcares, we often receive requests to block dynamic IP using CSF as a part of our Server Management Services.

Today, let’s discuss how our Support Engineers block the dynamic IP in the CSF firewall.


What is CSF and its advantages?

ConfigServer Firewall, also known as CSF, is a firewall configuration script created to provide better security to the servers. Also, it helps to block and allow the IP address on the server.

The CSF firewall application suite for Linux servers. It also checks for login authentication failures on mail servers, OpenSSH servers, Ftp servers so on.

Moreover, the CSF firewall restricts access by port number. And it has extra security features. The other thing is that we can simply install the CSF on the servers.

Let’s discuss the main advantages of CSF firewall

  1. It prevents the server from DoS attacks.
  2. Also, detect intrusion and other malicious content, traffic, and programs.
  3. CSF block bad IP addresses from gaining access to the server.
  4. It provides full control and management of the traffic entering and exiting on websites.

Moreover, in addition to the above-mentioned benefits, CSF also features Login Failure Daemon (LFD).  LFD periodically checks the server activities in a timed manner.

Also, LFD looks for attacks like brute-force login attempts. And if found any attacks it blocks the IP address attempting to attack that server. So most of the server owners prefer this firewall to secure their servers.


How we Block Domains Dynamic IP using CSF?

Till now we discussed the CSF firewall and its benefits. Now let’s see how our Support Engineers block the dynamic IP using the CSF firewall.

To do this, we followed the below steps to block the dynamic IP.

1. Firstly, we changed to the CSF directory.

cd /etc/csf

2. Then we opened the CSF configuration file with an editor.

vi csf.conf

3. Next, we searched  for “DYNDNS” on the file and can see some lines like below:

DYNDNS = “0”

That means the function is disabled. So we changed it to “300”. This check for updates every 5 minutes. Further, we turned on the DYNDNS_IGNORE option too.

Block Domains Dynamic IP using CSF

4. Next, we set up the time interval between the checks here.

We added the value to this parameter ‘GLOBAL_DYNDNS_INTERVAL’ in the CSF configuration file.


5. Then, we specified the domain that we need to block in the CSF. For this, we edited the csf.dyndns file.

vi /etc/csf/csf.dyndns

6. Finally, we restarted the CSF service to activate this.

csf -r

In this way, we blocked the domains having dynamic IPs using CSF for our customers.


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In short, sometimes there will be certain domains that have dynamic IPs and we cannot block a particular IP to block the domain on the server. Today we saw how our Support Engineers blocked the domains dynamic IP using the CSF.


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