Occurs when Cloudflare timed out while contacting the origin web server. Two different timeouts may cause the error depending on when they occur between Cloudflare and the origin web server:
- Before a connection is established, the origin web server does not return a SYN+ACK to Cloudflare within 15 seconds of Cloudflare sending a SYN.
- After a connection is established, the origin web server doesn’t acknowledge (ACK) Cloudflare’s resource request within 90 seconds.
Step 1: Contact NET Support
Contact NET to check the following common causes at your origin web server:
- Cloudflare IP addresses are rate limited or blocked in .htaccess, iptables, or firewalls. Ensure that the Cloudflare IP addresses are whitelisted.
- An overloaded or offline origin web server drops incoming requests.
- Keepalives are disabled at the origin web server.
- The origin IP address in your Cloudflare DNS app does not match the IP address currently provisioned to your origin web server by NET.
- Packets were dropped at your origin web server.
Step 2: Request Information
If none of the above solves the issue, request the following information from NET or site administrator before contacting Cloudflare support:
- An MTR or traceroute from your origin web server to a Cloudflare IP address that most commonly connected to your origin web server before the issue occurred. Identify a connecting Cloudflare IP recorded in the origin web server logs.
- Details from NET’s investigation such as pertinent logs or conversations with the hosting provider.