ASN

Autonomous System Number

A unique global identifier assigned to Autonomous Systems (AS) – the distinct networks that make up the Internet. Think of an ASN as a social security number for networks: just as each person has a unique SSN, each independently operated network needs its own ASN to be recognized and communicate on the Internet.

ASNs are managed and distributed by the Internet Assigned Numbers Authority (IANA) and the five Regional Internet Registries (RIRs). Originally, ASNs were 16-bit numbers ranging from 0 to 65535, but as the Internet grew, a new 32-bit format was introduced, expanding the available numbers into the millions.

In practical terms, when you see an ASN like AS7018 (AT&T) or AS8075 (Microsoft), you’re looking at the official identity of that organization’s network infrastructure. Network operators use these numbers to establish connections, manage routing policies, and troubleshoot connectivity issues between different parts of the Internet.

An ASN becomes necessary for businesses when they need to operate their own independent network with multiple connections to different Internet service providers or when they require direct control over their routing policies. However, most organizations connect through their ISP’s ASN rather than maintaining their own.

• Abbreviation: ASN