Accoding to RFC standard, the HEAD method is identical to GET except that the server MUST NOT return a message-body in the response. So, ADC treats the 302 response as an invalid http response and the reset the TCP connection.
ADC nstrace details:
After receiving the 302 response to the http request “HEAD /cgi/authenticate” from Citrix Gateway, LB Vserver does not transmit it to the client. Instead, sends “RST” with reset code 9206 to the client.
9206 | HTTP tracking failed due to invalid HTTP request/response header. |
The 302 response contains a message-body: