599 Network Connect Timeout Error
Non-standard proxy code indicating the proxy could not establish a connection to the upstream in time.
Status
HTTP/1.1 599 Network Connect Timeout Error
Details
- Category: 5xx
- Status: Unofficial (Legacy HTTP proxies). 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
599 is the connect-phase counterpart to 598: the proxy could not open a connection to the upstream before its timeout expired. Some HTTP client libraries also use 599 internally as a synthetic status for connection failures that never produced a real response.
The standard equivalents are 504 for a gateway timeout and 502 when the connection fails outright.
Common causes
- The upstream host was unreachable or dropped connection attempts.
- DNS resolution failure inside the proxy.
- A synthetic status generated by a client library for a transport-level failure.
How to fix it
As the client
- Retry with backoff. Confirm the destination resolves and is reachable from your network.
- Check whether the code came from your HTTP library rather than from a server, since several libraries synthesize it.
As the server
- Return 502 or 504 so the failure mode is expressed in a registered code.
Examples
HTTP/1.1 599 Network connect timeout error
Notes for proxy users
A 599 from a client library is usually a transport failure rather than a response from any server. Check DNS, the proxy endpoint and port, and whether the destination accepts connections at all before treating it as a target-side error.