Koko Uko

Author Archives: Koko Uko

Ending the “silent drop”: how Dynamic Path MTU Discovery makes the Cloudflare One Client more resilient

You’ve likely seen this support ticket countless times: a user’s Internet connection that worked just fine a moment ago for Slack and DNS lookups is suddenly hung the moment they attempt a large file upload, join a video call, or initiate an SSH session. The culprit isn't usually a bandwidth shortage or service outage issue, it is the "PMTUD Black Hole" — a frustration that occurs when packets are too large for a specific network path, but the network fails to communicate that limit back to the sender. This situation often happens when you’re locked into using networks you do not manage or vendors with maximum transmission unit (MTU) restrictions, and you have no means to address the problem.

Today, we are moving past these legacy networking constraints. By implementing Path MTU Discovery (PMTUD), the Cloudflare One Client has shifted from a passive observer to an active participant in path discovery.

Dynamic Path MTU Discovery allows the client to intelligently and dynamically adjust to the optimal packet size for most network paths using MTUs above 1281 bytes. This ensures that a user’s connection remains stable, whether they are on a high-speed corporate backbone or a restrictive cellular network.

The “modern Continue reading

A QUICker SASE client: re-building Proxy Mode

When you need to use a proxy to keep your zero trust environment secure, it often comes with a cost: poor performance for your users. Soon after deploying a client proxy, security teams are generally slammed with support tickets from users frustrated with sluggish browser speed, slow file transfers, and video calls glitching at just the wrong moment. After a while, you start to chalk it up to the proxy — potentially blinding yourself to other issues affecting performance. 

We knew it didn’t have to be this way. We knew users could go faster, without sacrificing security, if we completely re-built our approach to proxy mode. So we did.

In the early days of developing the device client for our SASE platform, Cloudflare One, we prioritized universal compatibility. When an admin enabled proxy mode, the Client acted as a local SOCKS5 or HTTP proxy. However, because our underlying tunnel architecture was built on WireGuard, a Layer 3 (L3) protocol, we faced a technical hurdle: how to get application-layer (L4) TCP traffic into an L3 tunnel. Moving from L4 to L3 was especially difficult because our desktop Client works across multiple platforms (Windows, macOS, Linux) so we couldn’t use Continue reading