def is_valid_ipv6_prefix(ipv6_prefix):
    """Returns True if given `ipv6_prefix` is a valid IPv6 prefix."""

    # Validate input type
    if not isinstance(ipv6_prefix, str):
        return False

    tokens = ipv6_prefix.split('/')
    if len(tokens) != 2:
        return False

    # Validate address/mask and return
    return is_valid_ipv6(tokens[0]) and is_valid_ip_prefix(tokens[1], 128)
Returns True if given `ipv6_prefix` is a valid IPv6 prefix.