title: What is HTTP "Host" header?
body: <p>Given that the TCP connection is already established when the HTTP request is sent, the IP address and port are implicitly known -- a TCP connection is an IP + Port.</p>
  <p>So, why do we need the <code>Host</code> header?  Is this only needed for the case where there are multiple hosts mapped to the IP address implied in the TCP connection?</p>