如何使用pcap4j库实现类似ping的功能

Question

我想实现基本的网络检查功能，以测试所提供的网址是否响应(例如。ping www.google.com).It必须提供操作信息，例如，指示请求的服务不可用或无法到达主机。我能够使用icmp4j库实现它。但是我想使用pcap4j库来实现同样的目标。我想把网址放在文本框中，然后点击连接按钮，这将调用pcap4j api来检查主机是否响应。

Answer 1

您可以使用IcmpV4EchoPacket、IcmpV4CommonPacket、IpV4Packet和EthernetPacket的构建器在以太网数据包上创建Echo (ping)，并通过PcapHandle.sendPacket()发送它们。请参阅pcap4j样例项目中的org.pcap4j.sample.SendFragmentedEcho。

您需要实现ARP来将IP地址解析为pcap4j示例项目中的org.pcap4j.sample.SendArpRequest等MAC地址。

您还需要实现一个功能，以便从给定的IP地址找到下一个跳(默认网关)。Pcap4J不提供支持此实现的API。(Java不提供API来获取路由表.)

你最好用java.net.InetAddress#isReachable()代替。

Answer 2

我花了一年多的时间才弄明白这一点，因为我想用pcap4j制作一个traceroute，下面是我所做的：

1. 获取您的IPv4地址和Mac地址，这可以通过查询PcapNetworkInterface轻松实现。
2. 获取目标IP地址，如果您有一个DNS名称，您需要事先解决它。
3. 获取目标Mac地址。
   1. 目标位于同一个子网中:发送一个ARP请求来解析mac (或者，mac广播也可能运行得很好)。
   2. 目标位于不同的子网中:您需要获得网关服务器的mac，这并不容易。假设您有其他网络流量，您可以侦听传入的数据包并获取源mac，其中源IP地址来自不同的子网，这很可能是网关服务器的mac地址。

4. 创建IcmpV4EchoPacket并发送
5. 侦听传入的ICMP通信量，您将得到以下三种中的一种：
   1. IcmpV4EchoReplyPacket，它可能是对您的请求的回答(请检查标识符和序列号以确保)
   2. 如果无法用指定的时间到达目标，则为IcmpV4TimeExceededPacket。
   3. 没有，路由器和被点击的目标可以自由地忽略和不响应你的要求。

需要填写的变量：

short IDENTIFIER; // identifer may be any 16 bit interger
short SEQUENCE; // sequence may be any 16 bit integer
byte TTL; // time to live (1-255)
Inet4Address IP_TARGET; // ip address of your ping target
Inet4Address IP_ORIGIN; // your own ip address
MacAddress MAC_TARGET; // target or gateway mac address
MacAddress MAC_SOURCE; // your own mac address
PcapNetworkInterface PCAP4J_NETWORK_INTERFACE; // network interface used to execute the ping

如何制作ICMP回波请求包(作为IcmpV4CommonPacket of IpV4Packet of EthernetPacket的有效负载)：

    public Packet buildPacket() {
        IcmpV4EchoPacket.Builder icmpV4Echo = new IcmpV4EchoPacket.Builder()
                .identifier(IDENTIFIER) // optional, default zero
                .sequenceNumber(SEQUENCE); // optional, default zero
        IcmpV4CommonPacket.Builder icmpV4Common = new IcmpV4CommonPacket.Builder()
                .type(IcmpV4Type.ECHO) // type is echo
                .code(IcmpV4Code.NO_CODE) // echo request doesn't need this
                .payloadBuilder(icmpV4Echo)
                .correctChecksumAtBuild(true);
        IpV4Packet.Builder ipv4Builder = new IpV4Packet.Builder()
                .correctChecksumAtBuild(true)
                .correctLengthAtBuild(true)
                .dstAddr(IP_TARGET) // IPv4 Address where tp send the request
                .payloadBuilder(icmpV4Common)
                .protocol(IpNumber.ICMPV4) // payload is ICMPV4
                .srcAddr(IP_ORIGIN) // Your own IPv4 Address
                .tos(IpV4Rfc1349Tos.newInstance((byte) 0))
                .ttl(TTL) // time to live (1-255)
                .version(IpVersion.IPV4); // IP Version is IPv4
        EthernetPacket.Builder etherBuilder = new EthernetPacket.Builder()
                .dstAddr(MAC_TARGET) // the targets mac address
                .srcAddr(MAC_SOURCE) // your own mac address
                .type(EtherType.IPV4) // payload protocl is IPv4
                .payloadBuilder(ipv4Builder)
                .paddingAtBuild(true);
        return etherBuilder.build(); // build your packet
    }

ICMP回声应答或超时的侦听器：

    public PacketListener buildListener() {
        return new PacketListener() {
            @Override
            public void gotPacket(Packet packet) {
                if (!(packet instanceof EthernetPacket))
                    return;
                EthernetPacket ethernetPacket = (EthernetPacket) packet;
                packet = ethernetPacket.getPayload();
                if (!(packet instanceof IpV4Packet))
                    return;
                IpV4Packet ipV4Packet = (IpV4Packet) packet;
                IpV4Header ipV4Header = ipV4Packet.getHeader();
                packet = ipV4Packet.getPayload();
                if (!(packet instanceof IcmpV4CommonPacket))
                    return;
                IcmpV4CommonPacket icmpPacket = (IcmpV4CommonPacket) packet;
                packet = icmpPacket.getPayload();
                // successful reply just measure time and done
                if (packet instanceof IcmpV4EchoReplyPacket) {
                    IcmpV4EchoReplyPacket icmpV4EchoReplyPacket = (IcmpV4EchoReplyPacket) packet;
                    IcmpV4EchoReplyHeader icmpV4EchoReplyHeader = icmpV4EchoReplyPacket.getHeader();
                    if (icmpV4EchoReplyHeader.getIdentifier() != identifier)
                        return;
                    if (icmpV4EchoReplyHeader.getSequenceNumber() != sequence)
                        return;
                    // here you got an echo reply
                    System.out.println(packet);
                    return;
                }
                // try handle time to live exceeded messages
                if (packet instanceof IcmpV4TimeExceededPacket) {
                    packet = packet.getPayload(); // original IPv4
                    if (!(packet instanceof IpV4Packet))
                        return;
                    packet = packet.getPayload(); // original ICMP common
                    if (!(packet instanceof IcmpV4CommonPacket))
                        return;
                    packet = packet.getPayload(); // original ICMP echo
                    if (!(packet instanceof IcmpV4EchoPacket))
                        return;
                    IcmpV4EchoHeader icmpV4EchoHeader = ((IcmpV4EchoPacket)packet).getHeader();
                    if (icmpV4EchoHeader.getIdentifier() != IDENTIFIER)
                        return;
                    if(icmpV4EchoHeader.getSequenceNumber() != SEQUENCE)
                        return;
                    // HERE you got an answer, that the time to live has been used up
                    System.out.println(packet);
                    return;
                }
            };
        }

把它结合起来：

    public static void main(String[] args) throws IOException, PcapNativeException, NotOpenException, InterruptedException {
        try (PcapHandle handle = PCAP4J_NETWORK_INTERFACE.openLive(1024, PromiscuousMode.PROMISCUOUS, 1000)) {
            // set filter to only get incoming ICMP traffic
            handle.setFilter("icmp and dst host " + Pcaps.toBpfString(IP_ORIGIN), BpfCompileMode.OPTIMIZE);
            // send ARP request
            Packet p = buildPacket();
            handle.sendPacket(p);
            // wait (forever) for ARP answer
            PacketListener listener = buildListener();
            handle.loop(-1, listener);
        }
    }