ASN (Autonomous System Number)
An ASN is a unique number assigned to an Autonomous System (AS)—a collection of IP networks and routers under the control of a single entity.
Key Role of ASNs: 1. Routing Policy: Allows networks to define whom they 'peer' with. 2. Traffic Engineering: Controlling how data enters and leaves a network. 3. DDoS Defense: Many CDNs filter traffic at the ASN level to block entire malicious networks. 4. Geolocation: Identifying the origin of IP traffic based on the registered owner of the ASN.
graph LR
Center["ASN (Autonomous System Number)"]:::main
Pre_proof_of_work["proof-of-work"]:::pre --> Center
click Pre_proof_of_work "/terms/proof-of-work"
Pre_hashing["hashing"]:::pre --> Center
click Pre_hashing "/terms/hashing"
Rel_gpu["gpu"]:::related -.-> Center
click Rel_gpu "/terms/gpu"
Rel_cpu["cpu"]:::related -.-> Center
click Rel_cpu "/terms/cpu"
Rel_antimatter_containment["antimatter-containment"]:::related -.-> Center
click Rel_antimatter_containment "/terms/antimatter-containment"
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classDef pre fill:#0f172a,stroke:#3b82f6,color:#94a3b8,rx:5,ry:5;
classDef child fill:#0f172a,stroke:#10b981,color:#94a3b8,rx:5,ry:5;
classDef related fill:#0f172a,stroke:#8b5cf6,stroke-dasharray: 5 5,color:#94a3b8,rx:5,ry:5;
linkStyle default stroke:#4b5563,stroke-width:2px;
🧒 Explique-moi comme si j'avais 5 ans
Think of the internet as a collection of different countries. Each country has its own internal roads (IP networks), but to travel between countries, you need to use the international highways. An [ASN](/fr/terms/asn) is like the official ID number for a country, letting the rest of the world know how to send mail or packages to its borders.
🤓 Expert Deep Dive
ASNs are categorized into Public and Private ranges. Public ASNs (0–64495 for 16-bit, and up to millions for 32-bit) are globally routable and assigned by RIRs like ARIN or RIPE. In BGP, the ASN is used in the AS_PATH attribute to prevent routing loops—if a router sees its own ASN in a path, it rejects the update. Modern network security heavily audits ASN advertisements to prevent 'BGP Hijacking', where a malicious AS falsely claims ownership of IP prefixes belonging to another ASN.