Test with the IP address first. If that works, the problem is only the name lookup.
What the message means
mDNS lets devices find each other by a name ending in .local. Support differs between systems, and some networks block it.
Fix it in this order
- Call MDNS.begin(“name”) after Wi-Fi connects and check that it returns true.
- Open http://name.local/ and, if that fails, open the IP address to confirm the server works.
- Check that your computer supports mDNS. Install the service software on older Windows if needed.
- Some routers and guest networks block multicast traffic.
- Use a fixed IP address or a router reservation as a simple alternative.
If you see this, do this
| You see | Do this |
|---|---|
| IP works, name does not | mDNS support or blocked multicast. |
| Neither works | See the web server page. |
Related
web server not reachable, Wi-Fi will not connect.
Last reviewed: November 2026. These are the usual causes and the order that finds them fastest. Test on your own board; clones and cables differ.