What to do when UDP is blocked

If the test could not send a single packet, your network is probably blocking UDP, and that affects far more than this test.

Updated

What the result means

The test on this site sends its packets over UDP to a relay on Cloudflare's network, using the standard TURN port 3478 and a fallback on port 443. If it cannot open that connection within ten seconds, it reports that UDP appears to be blocked. At that point no packets have gone anywhere, so there is no loss percentage to measure: the connection for this kind of traffic simply does not exist.

That matters because UDP is what real-time traffic uses. Most online games, WhatsApp and Discord voice, and Zoom, Teams and Meet audio and video all prefer UDP. When it is blocked, games usually fail to connect at all, and call apps fall back to sending media over TCP or HTTPS. The fallback works, but it adds delay and handles loss badly, because TCP stops and waits for every missing packet.

Why a network blocks UDP

  • Workplace and school networks often allow only web traffic, by policy, to limit games, streaming and file sharing.
  • Public wifi in hotels, airports and cafés is frequently locked down the same way.
  • Some VPNs carry only TCP, or run over TCP themselves, so UDP inside the tunnel never gets through.
  • Security software on the computer, or a strict router firewall setting, can block outgoing UDP.
  • Some mobile carriers and captive portals block or throttle UDP until you have signed in.

What you can do

  • Try another network: switch from wifi to mobile data, or vice versa. If the test works on one and not the other, the block is on the network that failed.
  • Turn off any VPN and run the test again.
  • Check the firewall or security software on the device. Temporarily disabling it for one test tells you whether it is the cause.
  • On your own router, look for settings named "UDP flood protection", "SIP ALG" or a strict firewall level, and try the default setting.
  • On a work or school network, ask the IT team. They may allow specific services such as Teams even if general UDP is blocked.

If it is blocked on purpose

On a managed network the block is a policy, and working around it may break the rules you agreed to. The practical answer is to use the services that network allows, or to run games and calls from a network you control. If the test fails at home on your own router, that is not a policy, and it is worth fixing: without UDP, every call you make is running on its fallback path.

Once UDP works, run the packet loss test again to see the connection's real quality.

Frequently asked questions

How do I know if UDP is blocked?

A UDP-based test like the one on this site will fail to connect at all. Games failing to find a server and call apps showing poor quality on a fast connection are other signs.

Does Zoom work without UDP?

Yes, it falls back to TCP and HTTPS, but calls are more likely to lag and stutter because TCP handles packet loss by waiting.

Is it safe to allow UDP?

Yes. Home routers allow outgoing UDP by default and block unsolicited incoming traffic. Blocking outgoing UDP is a policy choice, not a security requirement for home users.