filter-map rib-in-pre(
    output: Log,
    route: Route,
) {
    define {
        my_prefix = 100.40.0.0/17;
    }

    apply {
        if route.prefix_matches(my_prefix) {
            output.log_custom(10, 100);
            reject
        } else {
            output.log_prefix(my_prefix);
            accept
        }
    }
}