title: Session ID in DTLS (OpenSSL)
body: <p>I am trying to implement a DTLS server using OpenSSL. I can get app data through, but when the client and server have negotiated, I have noticed that the session_id is null on the server.</p>
  
  <p>Checking the code, more specifically ssl_sess.c, session_id_length is explicitly set to zero, the comments refer to RFC4507.</p>
  
  <p>My question is when the connection is negotiated, what ID can I use to uniquely identify a client?</p>
  
  <p>I have noticed that on the client side, the session id seems to be calculated from the ticket, but this does not seem to happen on the server. </p>