The Internet may look like a single space, but it actually consists of thousands of independent networks. To manage this global maze, every network gets a special identifier—an ASN.
If you’ve ever heard about bots, DDoS, proxies, or digital attacks, you’ve encountered ASN. But why is this parameter so important for cybersecurity, and how does it help detect suspicious traffic? Let’s break it down.
ASN (Autonomous System Number) is a unique identifier assigned to each autonomous system (AS) on the Internet. An autonomous system is a large network or group of networks managed by one organization with a single routing policy.
Examples:
Each autonomous system has its own ASN—think of it as a “passport” for networks on the Internet.
All internet routing is built on BGP (Border Gateway Protocol), which uses ASN to share information about the availability of networks. Every time someone visits your website, their IP address is linked to a specific ASN.
By checking ASN, you can see where traffic is coming from:
Automated and malicious traffic almost always originates from the same types of networks:
BotBlocker uses ASN to:
There are public databases (RIPE, ARIN, APNIC) and whois/IP lookup tools. Any IP address can be “looked up” to find its ASN and identify the organization controlling that IP range.
What is an autonomous system (AS)?
A network operated by one entity with a unique ASN in the global routing system.
Can a provider have multiple ASNs?
Yes, large companies or ISPs often use several ASNs for different networks or regions.
Why filter traffic by ASN?
It helps block mass bots, data center attacks, and anonymizers while allowing real users through.
Can you block an entire malicious network by ASN?
Absolutely. Blocking by ASN quickly filters out all IPs from a specific provider or hosting.
