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GeoDNS vs Anycast: Geographic Traffic Steering

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Geographic routing: getting users to the nearest data center

Sending a user in Frankfurt to a data center in Virginia adds ~80ms of avoidable round-trip latency. For a global service, geographic routing is essential: users in Europe should reach European servers, users in Asia should reach Asian servers.

Two mechanisms solve this at different layers: GeoDNS at the application layer (returns different IPs per DNS query based on location), and Anycast at the network layer (multiple data centers announce the same IP prefix, BGP routes to nearest). Major CDNs use both.

Packets in motion — click to inspect:

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