code: def is_valid_vpnv6_prefix(prefix):
      
      if not isinstance(prefix, str):
          return False
  
      # Split the prefix into route distinguisher and IP
      tokens = prefix.split(':', 2)
      if len(tokens) != 3:
          return False
  
      # Validate route distinguisher
      if not is_valid_route_dist(':'.join([tokens[0], tokens[1]])):
          return False
  
      # Validate IPv6 prefix and return
      return is_valid_ipv6_prefix(tokens[2])
docs: Returns True if given prefix is a string represent vpnv6 prefix.
  
      Vpnv6 prefix is made up of RD:Ipv6, where RD is represents route
      distinguisher and Ipv6 represents valid colon hexadecimal notation string.