import ipaddress


def get_ipv6_interface_id(ipv6: str) -> str:
    """
    Retrieve the interface id out of the lower 64 bits
    """
    ipv6_block = ipaddress.ip_address(ipv6)
    interface = ipaddress.ip_address(int(ipv6_block) & 0xffffffffffffffff)

    return str(interface)