This is the result of a known issue. The CLIENT_ACCEPTED iRule event prevents the BIG-IP LTM from inserting HTTP headers because the BIG-IP LTM has not parsed the HTTP headers when the iRule is triggered. As a result, TMM may crash.

F5 Product Development tracked the TMM crash associated with this behavior as CR44578 and CR50798 and it was fixed in BIG-IP LTM versions 9.1.1 and 9.2.0. For information about upgrading, refer to the BIG-IP LTM release notes.

The CLIENT_ACCEPTED iRule event is intended for use with Layer 4 traffic, but is not intended for use with HTTP. It is still not possible to perform the HTTP header insert because the BIG-IP LTM has not parsed the HTTP headers when the CLIENT_ACCEPTED iRule event is triggered. However, attempting to use the CLIENT ACCEPTED iRule event with HTTP will no longer cause TMM to crash.

Workaround

You can work around this issue by basing your iRule on the HTTP_REQUEST event. This event is intended to be used with HTTP, allowing the BIG-IP LTM to correctly parse the headers and successfully perform HTTP manipulations.