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This article explains how Cloudflare implemented Dynamic Path MTU Discovery (PMTUD) in the Cloudflare One Client to eliminate silent packet drops caused by MTU mismatches on network paths.
•The "PMTUD Black Hole" occurs when oversized packets hit a network hop with a lower MTU limit, but firewalls silently drop ICMP feedback messages, causing connections to hang indefinitely
•Cloudflare implemented RFC 8899 PMTUD using the MASQUE protocol built on their open-source QUIC library to actively probe network paths instead of relying on legacy ICMP feedback
•The client proactively sends encrypted probe packets of varying sizes to the Cloudflare edge to binary-search the exact optimal MTU for each network segment
•The virtual interface MTU is dynamically resized on the fly and periodically revalidated as network conditions change (e.g., switching from Wi-Fi to cellular)
•Use cases include first responders on vehicle-mounted routers with complex NAT layers and hybrid workers encountering
This summary was automatically generated by AI based on the original article and may not be fully accurate.
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