title: How to generate random IPv6 address using Python(or in Scapy)?
body: <p>In my test case, I need to send out NA with random IPv6 source address and fixed prefix.
  For example:</p>
  
  <p>fixed prefix 2001::cafe:/64. The remainder of the address should be random.</p>
  
  <p>How to achieve in Python or in Scapy?</p>