Solution | Compare a small and large test file using the same application and destination. Verify commands on the installed release: Collect a browser HAR and record the failing URL, HTTP method, file size, time and status. Check application/server logs. A 413 suggests a size limit; a 417 relates to an expectation failure. Identify which device generated the response. Use GUI packet capture on both proxy connections. A quick CLI timeline is:
diagnose sniffer packet any 'host <client-IP> or host <server-IP>' 4 0 l
Start before a fresh upload; stop with Ctrl + C. Use PCAP to check retransmissions, zero windows and resets. HTTPS packet captures alone do not reveal request headers or bodies.
If HTTP processing remains unclear, collect a short filtered WAD HTTP trace. Coordinate before resetting diagnostics:
diagnose debug reset
diagnose wad debug clear
diagnose wad filter clear
diagnose wad filter src <client-IP>
diagnose wad debug enable category http
diagnose wad debug enable level verbose
diagnose debug enable
Reproduce once, then stop and clear:
diagnose debug disable
diagnose wad debug clear
diagnose wad filter clear
diagnose debug reset
Interpret and correct:
Headers sent but body not sent: check Expect: 100-continue and the interim/final response. Missing 100 alone is not proof of failure. Body reaches FortiProxy but forwarding stalls: check matched AV/DLP/ICAP settings, logs and resource pressure; some inspection buffering is expected. Body reaches the server: check its upload limit, processing time and response. Repeated packets or zero windows: investigate loss, MTU or receiver backpressure.
Example only: A server-generated 413 after upload headers points to an upstream size limit, not a transport fault. Correct the confirmed limit, framing issue, inspection setting or network fault. If isolating a profile, use a temporary test policy restricted to the test client and destination, then restore it.
Verify the same upload completes and intended inspection still applies. Do not globally disable inspection or increase all timeouts. Redact credentials and uploaded content before sharing captures.
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