import socket


def is_valid_ipv6_address(address: str) -> bool:
    """
    >>> is_valid_ipv6_address('::1')
    True
    >>> is_valid_ipv6_address('127.0.0.1')
    False
    >>> is_valid_ipv6_address('unknown')
    False

    """
    try:
        socket.inet_pton(socket.AF_INET6, address)
    except socket.error:  # not a valid address
        return False
    return True