Limits RegistryPUBLIC RECORD
Limits RegistryThe original Border Gateway Protocol used a 16-bit Autonomous System Number field, capping the internet's total routable AS numbers at 65,536 — a space that was projected to run out as the number of internet-connected organizations grew. RFC 6793, standardized in 2012, extended the ASN field to 32 bits, expanding the total addressable space to roughly 4.29 billion Autonomous System Numbers, since deployed across the global internet's routing infrastructure.
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The original Border Gateway Protocol used a 16-bit Autonomous System Number field, capping the internet's total routable AS numbers at 65,536 — a space that was projected to run out as the number of internet-connected organizations grew. RFC 6793, standardized in 2012, extended the ASN field to 32 bits, expanding the total addressable space to roughly 4.29 billion Autonomous System Numbers, since deployed across the global internet's routing infrastructure.
The total number of unique Autonomous System Numbers addressable under RFC 6793's 4-byte ASN extension to the Border Gateway Protocol, fixed by its 32-bit field width, up from the original 16-bit (65,536-number) space.
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The frontier as it changed over time.
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Permanent ID limitsregistry.com/limits/LR-4BYTE-BGP-ASN-SPACE
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Limits Registry. LR-4BYTE-BGP-ASN-SPACE. Expanded Border Gateway Protocol Autonomous System Number space. 2026.