How they fit together
Stack them from smallest to largest: an IP address sits inside a CIDR block, and a CIDR block is announced by an ASN. When you look up an IP, the lookup walks up that stack to tell you the CIDR block and the ASN behind it. You can try it on any IP with the ASN Lookup tool.
Why the distinction matters
For fraud and routing, the ASN is the level that tells you who operates an address. Two IPs in different CIDR blocks can belong to the same ASN, so checking the ASN groups traffic by operator. How an IP resolves to its ASN is covered in IP-to-ASN mapping, and the risk angle in Abstract's IP Intelligence API.
Frequently Asked Questions
What is the difference between an ASN and an IP address?
An IP address identifies a single endpoint. An ASN identifies the whole network that owns and routes the range of IP addresses that endpoint belongs to.
What is the difference between a CIDR block and an ASN?
A CIDR block is a range of IP addresses, like 8.8.8.0/24. An ASN is the network operator that announces one or more of those blocks to the internet.
How are IP, CIDR, and ASN related?
An IP address sits inside a CIDR block, and a CIDR block is announced by an ASN. They are three levels: a single address, a range, and the operator.
Can one ASN have multiple CIDR blocks?
Yes. A single ASN usually announces many CIDR blocks, and each block contains many individual IP addresses.
Why does the ASN matter more than the IP for fraud?
The ASN groups addresses by operator, so it tells you whether traffic comes from a residential ISP or a data center, which a single IP alone does not.
