code: def is_valid_vpnv4_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 IPv4 prefix and return
      return is_valid_ipv4_prefix(tokens[2])
docs: Returns True if given prefix is a string represent vpnv4 prefix.
  
      Vpnv4 prefix is made up of RD:Ipv4, where RD is represents route
      distinguisher and Ipv4 represents valid dot-decimal ipv4 notation string.