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IPv4 security. Part 2. IPv4 Monitoring. Tools to monitor IPv4 subnets and ASNs

IPv4 security. Part 2. IPv4 Monitoring. Tools to monitor IPv4 subnets and ASNs

In this part of our 3-parts tutorial we share the most important tools to monitor your internet number resources and autonomous system numbers on block lists.

  • Let’s monitor ASN

We recommend you to do an AS spam check of your future customer before the assignment.


This tool shows how many IPv4 addresses are announced with the exact ASN and which part of these IPv4 addresses were used for spamming. It also shows spam a monthly spam activity from ASN.

The main page shows ASNs with top spamming rates.

MX Toolbox

This tool displays all the IPv4 subnets which are announced by specified ASN

When you know the full list of subnets your customer announces, you can check them with IPv4-block lists on fraud, phishing and spamming issues and make a final decision.

  • Now, when we checked Autonomous System, let’s monitor IPv4 addresses

For IPv4 spam check we prefer to use the following tools:


This tool monitors around 50 well-known spam and other blacklistings. If it displays that IPv4 address is blacklisted, just follow the offered link to the spamlist to check the further details.


Spamhaus has two main types of listings: PBL and SBL.

When a subnet is listed in PBL, it doesn’t mean that it was used for illegal activities. You can easily delist a subnet with one click in your spamhaus account.

When a subnet is listed in SBL, this means that the user did illegal activity or sent spam. Don’t trust customers who have subnets listed in SBL.

Hidden Listings

There are other hidden spam listings, such as Hotmail and Yahoo. Unfortunately, we didn’t find any lookup where we can check it online without announcing a subnet – if you know any, please let us know and we will update this article. Moreover, Hotmail and Yahoo don’t reach you through abuse contacts in RIR databases. The best solution to monitor IP subnets on these listings is to register an account on behalf of IP-resources owner and add all subnets you have to created mailing monitoring account. When someone sends spam, you will receive a notification to your email.

  • Now, when we checked ASN and IP-addresses, we can check domains the customer would like to use for rDNS records

MX Toolbox Blacklists

Open the link above and specify a domain of your customer. As example, he provided:; – you can check and on block lists to ensure you won’t have any problems to create this domain object.

Now, we checked ASN on spamlistings and detected other subnets it announces, monitored IPv4 subnets and domain records on block lists. Hope this short tutorial will help you to detect dangerous customers.

In the third part we will share the cleaning process tips for those who found his subnets blacklisted and describe IP-delististing procedures of 3 well-know spamlistings (Spamhaus, Hotmail, Yahoo).

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