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3280423 - *** ERROR => forbidden protocol upgrade to h2c


When accessing a custom URL provided by a reverse proxy to the backend system, a "403 Access Denied" error is thrown at the browser.

Upon checking a dev_icm trace file (at least level 2) from the affected backend instance, there is an entry like below

[Thr 140425534674688] *** ERROR => forbidden protocol upgrade to h2c {00231e05} [http_plg.c 6627]
[Thr 140425534674688]              role: Server, protocol: HTTP, local: <backend instance IP>:<backend instance port>, peer: <reverse proxy IP>:<reverse proxy port>
[Thr 140425534674688] *** ERROR => HttpPlugInHandleNetData: HttpParseRequestHeader failed (rc=701) [http_plg.c   2513]



ABAP Platform all versions

SAP NetWeaver 7.4 or higher

SAP Kernel 749 or higher


ABAP platform all versions ; SAP NetWeaver all versions


HttpParseRequestHeader failed, forbidden protocol upgrade to h2c, HTTP/2, reverse proxy, ICM , KBA , BC-CST-IC , Internet Communication Manager , BC-CST-WDP , Web Dispatcher , Problem

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