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523 Origin Is Unreachable

Cloudflare could not reach the origin at all, usually a DNS or routing failure.

Status

HTTP/1.1 523 Origin Is Unreachable

Details

  • Category: 5xx
  • Status: Unofficial (Cloudflare). Not registered with IANA. A server, framework, or CDN convention.
  • Specification: none, not defined by any RFC
  • Cacheable: Not cacheable
  • Response body: Allowed
  • Retry: Retry after a delay

523 means the origin address could not be reached: the DNS record points at an address with no route, the host is gone, or an intervening network is dropping traffic entirely.

It differs from 521 and 522 in that the problem is finding the origin rather than connecting to a known one.

Common causes

  • A DNS record pointing at a stale or wrong IP address after a migration.
  • The origin host terminated or moved without updating DNS.
  • Network or routing failure between Cloudflare and the origin network.

How to fix it

As the client

  • Retry later. The origin is unreachable from the edge and no client-side change affects that.

As the server

  • Verify the origin DNS records point at the current server address.
  • Confirm the origin is routable from outside its own network, not just from within it.

Examples

An origin Cloudflare cannot route to

HTTP request

GET / HTTP/1.1
Host: www.example.com

HTTP response

HTTP/1.1 523
Server: cloudflare

See also