五条路由都能到这个地址，电脑为什么偏要走最细的那一条？

"""IPv4 longest-prefix teaching lookup; never reads or writes OS routes."""
import itertools
import json
from ipaddress import IPv4Address, IPv4Network


def build_table(entries):
    table = []
    networks = set()
    for cidr, next_hop in entries:
        network = IPv4Network(cidr, strict=True)
        if network in networks:
            raise ValueError("duplicate prefix: equal-prefix route policy is outside this model")
        networks.add(network)
        table.append((network, next_hop))
    return table


def lookup(table, destination):
    address = IPv4Address(destination)
    matches = [(network, hop) for network, hop in table if address in network]
    if not matches:
        return None
    network, hop = max(matches, key=lambda route: route[0].prefixlen)
    return {"prefix": str(network), "next_hop": hop}


def main():
    entries = [("0.0.0.0/0", "default"), ("10.0.0.0/8", "campus"),
               ("10.20.0.0/16", "building"), ("10.20.30.0/24", "lab"),
               ("10.20.30.7/32", "single-host")]
    expected = {"10.20.30.7": "10.20.30.7/32", "10.20.30.8": "10.20.30.0/24",
                "10.20.9.8": "10.20.0.0/16", "10.9.8.7": "10.0.0.0/8",
                "192.0.2.1": "0.0.0.0/0"}
    table = build_table(entries)
    checks = 0
    for permutation in itertools.permutations(entries):
        reordered = build_table(permutation)
        for address, prefix in expected.items():
            assert lookup(reordered, address)["prefix"] == prefix
            checks += 1
    assert lookup(build_table(entries[1:]), "192.0.2.1") is None
    checks += 1
    for invalid in [[("10.20.30.7/24", "bad")],
                    [("10.0.0.0/8", "a"), ("10.0.0.0/8", "b")]]:
        try:
            build_table(invalid)
            raise AssertionError("invalid table accepted")
        except ValueError:
            checks += 1
    smaller = build_table([row for row in entries if row[0] != "10.20.30.7/32"])
    fallback = lookup(smaller, "10.20.30.7")
    assert fallback["prefix"] == "10.20.30.0/24"
    checks += 1
    assert lookup([], "10.1.2.3") is None
    checks += 1
    report = {"checks_passed": checks,
              "results": {address: lookup(table, address) for address in expected},
              "after_removing_host_route": fallback,
              "wrong_first_match": str(next(network for network, _ in table
                                            if IPv4Address("10.20.30.7") in network)),
              "boundary": "static IPv4 teaching model; no ECMP, policy routing, metrics or packets"}
    print(json.dumps(report, indent=2, ensure_ascii=False))


if __name__ == "__main__":
    main()