32 Bit Real Estate

Summary

Fly.io’s globally distributed network needs routable IPv4 addresses because it assigns distinct public addresses to applications, including non-HTTP services such as UDP DNS servers and TCP game servers. The post explains how address control depends on Regional Internet Registry transfers, a BGP4 ASN, upstream peering, and advertising the same address from multiple locations for Anycast routing. IPv6 and TLS SNI can reduce address demand, but IPv6 connectivity remains unreliable for many users and SNI does not cover non-TLS applications; keeping separate provisioning paths is also considered undesirable. IPv4 blocks are therefore bundled with apps, while outright acquisition is preferred to leasing because addresses can remain assigned indefinitely, despite future IPv6 obsolescence and the risk that their value could eventually fall to zero.

Takeaways

1. 1

   Controlling an IPv4 block involves demonstrating authority over its prefixes, completing an RIR transfer, obtaining an ASN, and getting upstream providers to accept route announcements.

2. 2

   TLS SNI can share IPv4 addresses for TLS applications, but it does not support apps without TLS, including some DNS, game-server, and media-relay use cases.

3. 3

   Leasing IPv4 addresses would reduce inventory risk and potentially provide more capacity, but fixed terms and renewal dependence make it unsuitable for addresses intended to remain assigned indefinitely.