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Dev.to
7/20/2026
Whose ASN Goes on Your Leased IPv4 Prefix?

Whose ASN Goes on Your Leased IPv4 Prefix?

Short summary

A detailed technical guide on choosing the correct origin ASN for leased IPv4 prefixes, covering four deployment paths and their RPKI/ROA requirements. It explains why mismatched ASNs cause partial route drops that look like application bugs, and provides concrete commands for validation. Includes specific configuration details for AWS BYOIP, Azure Custom IP Prefix, and RIPE ASN assignment requirements.

  • •Four options for originating leased IPv4 prefixes: own ASN, upstream, cloud BYOIP, or third-party AS—each with different ROA requirements
  • •ROA.asID must match the origin AS and maxLength must cover the actual announcement or peers drop your prefix
  • •Covers AWS, Azure, and RIPE-specific constraints including BYOASN and multihoming requirements

Generated with AI, which can make mistakes.

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