Cloudflare Introduces Dynamic Path MTU Discovery in Cloudflare One Client

Cloudflare has announced the implementation of Path MTU Discovery (PMTUD) in its Cloudflare One Client, a feature that enables the client to dynamically adjust to the optimal packet size for most network paths. This ensures that a user's connection remains stable, whether they are on a high-speed corporate backbone or a restrictive cellular network. The new feature uses active probing with PMTUD to remove the reliance on fragile, legacy feedback loops.

Key Technical Details:

• The Cloudflare One Client uses the MASQUE protocol, built on top of Cloudflare's open-source QUIC library, to perform active, end-to-end interrogation of the network path.
• The client sends encrypted packets of varying sizes to the Cloudflare edge to test MTUs from the upper bound of the supported MTU range to the midpoint.
• The client dynamically resizes its virtual interface MTU on the fly by periodically validating the capacity of the path established at connection onset.

Practical Implications for Developers:

• The new feature ensures that users can maintain a stable connection even when moving between different network paths with varying MTUs.
• Developers can rely on the Cloudflare One Client to handle PMTUD, reducing the complexity of implementing this feature in their own applications.
• The Cloudflare One Client's dynamic MTU adjustment ensures that applications can continue to function smoothly even when faced with network constraints.