将有效负载数据添加到 pcap.net 中的 ICMP Echo Reply

Question

使用适用于 Windows 的 PCAP.NET 库，我可以根据文档构建 ICMP 回复数据包：

'''

   private static Packet BuildIcmpPacket(string sourcemac, string destmac, string sourceip, string targetip,int id, int seq,byte[] payload)
    {
        EthernetLayer ethernetLayer =
            new EthernetLayer
            {
                Source = new MacAddress(destmac),
                Destination = new MacAddress(sourcemac),
                EtherType = EthernetType.None, // Will be filled automatically.
            };

        IpV4Layer ipV4Layer =
            new IpV4Layer
            {
                Source = new IpV4Address(targetip),
                CurrentDestination = new IpV4Address(sourceip),
                Fragmentation = IpV4Fragmentation.None,
                HeaderChecksum = null, // Will be filled automatically.
                Identification = 123,
                Options = IpV4Options.None,
                Protocol = null, // Will be filled automatically.
                Ttl = 100,
                TypeOfService = 0,
            };

        IcmpEchoReplyLayer icmpLayer =
            new IcmpEchoReplyLayer
            {
                Checksum = null, // Will be filled automatically.
                Identifier = (ushort)id,
                SequenceNumber = (ushort)seq,
                //Payload =  payload,
            };
        
        PacketBuilder builder = new PacketBuilder(ethernetLayer, ipV4Layer, icmpLayer);

        return builder.Build(DateTime.Now);
    }
    

'''

我为以太网和 IPV4 层提供了 MAC 地址和 IP 地址，而不是示例默认值。

数据包生成器工作，我可以将其发送到线路，但请求主机无法识别答复（wireshark 看到它们，但请求被标记为“未找到答复”）。

我猜测 ID 和序列字段需要在回复中重复（我已提供），但我无法添加 ping 请求中的有效负载。我可以使用以下代码片段来阅读它：

'''

communicator.ReceivePacket(out wpacket);
if (wpacket == null)continue;
EthernetDatagram edg = wpacket.Ethernet;
IpV4Datagram ipv4 = edg.IpV4;
IcmpEchoDatagram icmpdg = (IcmpEchoDatagram)ipv4.Icmp;
int ID = icmpdg.Identifier;
int SEQ = icmpdg.SequenceNumber;
byte[] payload = icmpdg.Payload.ToArray();

'''，

但我没有找到将有效负载数据添加到回复中的方法。注意：此数据包生成器确实有效；一旦我将 ID 和序列号添加到回复中，发送主机就会看到它，但它抱怨没有收到数据。这实际上足以满足我的需求，但我想添加 paylaod 数据以发送“合法”的 ping 回复。

Answer 1

我通过进一步挖掘 github 上的示例代码找到了答案：

上面显示的 BuildIcmpPacket() 的原始代码使用这些层构建了数据包：

PacketBuilder builder = new PacketBuilder(ethernetLayer, ipV4Layer, icmpLayer);
return builder.Build(DateTime.Now);

只需添加 PayloadLayer 即可将有效负载添加到最终数据包中。为该有效负载提供的缓冲区（“payloadBuffer”）是从 ping 请求（上面）中读取的缓冲区。

...
IcmpEchoReplyLayer icmpLayer =
    new IcmpEchoReplyLayer
    {
        Checksum = null, // Will be filled automatically.
        Identifier = (ushort)id,
        SequenceNumber = (ushort)seq,
    };
PayloadLayer payloadLayer = 
new PayloadLayer
{
    Data = new Datagram(payloadBuffer, 0, payloadBuffer.Length),
};

PacketBuilder builder = new PacketBuilder(ethernetLayer, ipV4Layer, icmpLayer,payloadLayer);
return builder.Build(DateTime.Now);

ping 回复现在按预期工作，发件人对回复感到满意。