Keep large responses from stalling on VPC networks - #452
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Encapsulated traffic between locations adds a 40-byte outer IPv6 header. Measured on a staging cell, inner packets larger than 1440 bytes are silently dropped by the provider underlay with no Packet Too Big, so connections carrying large responses hang. Networks created from now on default to 1440; existing Networks keep their persisted value. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
privateip
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Sep 13, 2026
scotwells
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Large responses from Instances on a VPC network can stall: the headers arrive, but the body never does, and nothing reports an error. The provider underlay silently drops packets sized for today's default MTU of 1460. New Networks now default to 1440, the largest size proven to deliver in staging.
Existing Networks keep the MTU they already have, and a running Instance picks up a new value only when it is recreated.
For general-purpose Instances, this takes effect together with datum-cloud/galactic#533. Related: datum-cloud/galactic#532.
1440 was measured on one provider's network. A path with more overhead may need a lower value.
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