code: def _check_rf_and_normalize(prefix):
          
          addr, masklen = prefix.split('/')
          if ip.valid_ipv6(addr):
              # normalize IPv6 address
              ipv6_prefix = str(netaddr.IPAddress(addr)) + '/' + masklen
              return vrfs.VRF_RF_IPV6, ipv6_prefix
          else:
              return vrfs.VRF_RF_IPV4, prefix
docs: check prefix's route_family and if the address is
          IPv6 address, return IPv6 route_family and normalized IPv6 address.
          If the address is IPv4 address, return IPv4 route_family
          and the prefix itself.