ASN (Autonomous System Number)
An ASN identifies an autonomous system in BGP routing.
Updated: 2026-03-05
Definition
An Autonomous System Number (ASN) uniquely identifies a routing domain that runs a consistent routing policy.
BGP uses ASNs to track paths and prevent routing loops between autonomous systems.
Key points
- Identity for a routing domain
- Used in BGP path decisions and loop prevention
- Common in ISP and multi-homing designs
Common mistakes
- Confusing ASN with IP addressing.
- Forgetting that AS path is used for loop prevention.
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