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What is IP blocklisting?

  • Last Updated : 22 Oct, 2021

An IP blocklist, formerly known as a blocklist, is one of the simplest and most effective kinds of access denial in the world of computers. Blocklists are lists that comprise IP address ranges or single addresses that you want to prohibit. These lists can be used in conjunction with firewalls, intrusion prevention systems (IPS), and other traffic-filtering software for securing systems.

Why does an IP address get blocklisted?
In any case, adding an IP address to an IP blocklist is mostly due to one of the following reasons:

  1. Spam is sent on purpose, or daily sending limits are exceeded,
  2. Email receivers marked received communications as spam.
  3. A mailing server is hacked and used to mass send spam or harmful emails.
  4. Cybercriminals took control of a domain and used it for illicit purposes.
  5. Someone on the network is infected with malware.
  6. The gadget is infected with dubious software.
  7. The IP address is linked to a potentially dangerous website.
  8. A prior user had utilized the IP address in an unfavorable manner.


Types of IP Blocklists :
There are four types of IP Blocklists –  

  1. Email-based blocklists –
    An email blocklist functions as a spam filter, ensuring that emails that are potentially dangerous or spam do not reach the intended recipient.
  2. Domain Name System/DNS-based blocklists –
    A DNS-based blocklist operates by matching domain names to IP addresses that may be involved with spam or possibly dangerous emails.
  3. Phishing-based blocklists –
    Blocklists like those provided by Google Safe Browsing, PhishTank, and OpenPhish were created to detect phishing and malware-related activities on websites
  4. Malware-based blocklists –
    When a website is blocklisted as a result of harmful behavior, databases alert webmasters of the flagged sites to the impending IP blocklisting.
IP Blocklisting

IP Blocklisting

DNS blocklist and email blocklist are linked. Similarly, phishing blocklist and malware blocklist are linked. 


Challenges :
Although blocklisting is an effective strategy to restrict specific IP addresses from accessing your network, it is not without flaws. This is due to the fact that attackers have devised a variety of methods to circumvent blocklisting. A few instances of these strategies are as follows:

  1. Changing IP addresses –
    In order to avoid being blocklisted, many attackers keep changing their IP addresses. Criminals may have a variety of addresses to choose from, allowing them to shift addresses if one is blocklisted.
  2. IP spoofing –
    Attackers can employ IP spoofing to make it look as if they are connected via a different IP address in network layer attacks (e.g. DDoS attacks). This allows them to avoid being blocklisted while concealing their identities.
  3. Botnets –
    Thousands to millions of end-user devices or Internet of Things (IoT) devices are used by many attackers in enormous botnets. Attackers hack these devices and gain control of them, or rent a botnet as a service on the dark web in many circumstances.
  4. False positives –
    False positives are another issue you may encounter while using blocklists. Despite the fact that these issues are unrelated to attackers or security, they can nonetheless disrupt productivity.
  5. Inaccurate IP detection –
    Another problem arises when numerous people share the same IP address. When IP addresses are assigned dynamically, there is no means of knowing who is currently utilizing the address. This means that blocking one user for abusive behavior may prohibit a genuine user from accessing your network in the future.

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