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HTTP/1.1 400 Bad Request when using CICS as an HTTP server

Troubleshooting


Problem

You are using CICS Transaction Server for z/OS (CICS TS) as an HTTP server. You are noticing on certain requests, CICS is sending out an HTTP/1.1 400 Bad Request as the response. Other requests from the same application work fine.

Symptom

You notice that when the size of the request the application sends out is greater than 32K in size, CICS responds with the HTTP 1.1 400 Bad Request. If the size of the request is smaller than 32K, then it works fine.

Cause

The size of the request is larger than the MAXDATALEN parameter set on the CICS TCPIPService Definition.

Resolving The Problem

Change the MAXDATALEN parameter in the CICS TCPIPService definition so that the size of the request will fit within the MAXDATALEN. The Default value is 32 KB.

[{"Product":{"code":"SSGMGV","label":"CICS Transaction Server"},"Business Unit":{"code":"BU048","label":"IBM Software"},"Component":"Not Applicable","Platform":[{"code":"PF035","label":"z\/OS"}],"Version":"5.1;4.2;4.1;3.2;3.1","Edition":"","Line of Business":{"code":"LOB70","label":"Z TPS"}}]

Document Information

Modified date:
05 January 2026

UID

swg21461834

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