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在命令行输入ifconfig,查看本机网络接口。
$ ifconfig
enp4s0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether c8:5b:76:f6:44:d2 txqueuelen 1000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1000 (Local Loopback)
RX packets 391 bytes 61933 (60.4 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 391 bytes 61933 (60.4 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
virbr0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.122.1 netmask 255.255.255.0 broadcast 192.168.122.255
ether 52:54:00:a7:e6:9c txqueuelen 1000 (Ethernet)
RX packets 31 bytes 3291 (3.2 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 18 bytes 2571 (2.5 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
vnet0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet6 fe80::fc54:ff:fe15:2983 prefixlen 64 scopeid 0x20<link>
ether fe:54:00:15:29:83 txqueuelen 1000 (Ethernet)
RX packets 31 bytes 3725 (3.6 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 39 bytes 4941 (4.8 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
wlp5s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.1.1.64 netmask 255.255.255.0 broadcast 10.1.1.255
inet6 fe80::40df:807c:eb38:8b78 prefixlen 64 scopeid 0x20<link>
ether a8:6b:ad:54:d5:3d txqueuelen 1000 (Ethernet)
RX packets 10965 bytes 11639278 (11.1 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 3369 bytes 513997 (501.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
运行一段Java代码,往内网ip192.168.122.217发送UDP数据
package UDPtest;
import java.io.IOException;
import java.net.*;
public class UDPTestClient {
private static final int PORT = 8800;
private static final String HOSTNAME = "192.168.122.217";
public static void main(String[] args){
try (DatagramSocket ds = new DatagramSocket(8801)){
/**
* 这里是发送数据到服务端
*/
//这里定义地址信息
InetAddress id = InetAddress.getByName(HOSTNAME);
//要发送的数据
byte[] buffer = "这里是客户端发送的数据".getBytes();
//将数据打包成udp数据包
DatagramPacket dp = new DatagramPacket(buffer, buffer.length,id,PORT);
//发送数据包
ds.send(dp);
/**
* 这里是从服务端接收数据
*/
byte[] data2 = new byte[1024];
DatagramPacket packet2 = new DatagramPacket(data2,data2.length);
ds.receive(packet2);
String info = new String(data2,0,packet2.getLength());
System.out.println("我是客户端 从服务端收到的数据 info = " + info);
} catch (IOException e) {
e.printStackTrace();
}
}
}
在所有列出的网卡中找到正在运行的网卡,即flags=4163<UP,BROADCAST,RUNNING,MULTICAST>
有RUNNING字段的网卡。这里有lo,wlp5s0,vnet0,显然lo是本地回环接口,vnet0才是我们要找到的网卡。
回到wireshark,双击vnet0,开始监听。执行UDPTestClient
类,找到发送的数据包。
其中Source 10.1.1.64->Destination 192.168.122.217就是我们发送的数据包。双击查看数据包详细信息。
第一个目录下的Interface看到是无线网卡接口
Interface id: 0 (vnet0) Interface name: vnet0
第二个目录,以太网口
Ethernet II, Src: HonHaiPr_54:d5:3d (a8:6b:ad:54:d5:3d), Dst: Tp-LinkT_06:67:7d (74:05:a5:06:67:7d) Destination: Tp-LinkT_06:67:7d (74:05:a5:06:67:7d) Address: Tp-LinkT_06:67:7d (74:05:a5:06:67:7d) .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default) .... ...0 .... .... .... .... = IG bit: Individual address (unicast) Source: HonHaiPr_54:d5:3d (a8:6b:ad:54:d5:3d) Address: HonHaiPr_54:d5:3d (a8:6b:ad:54:d5:3d) .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default) .... ...0 .... .... .... .... = IG bit: Individual address (unicast) Type: IPv4 (0x0800)
Src代表源设备,Dst指目的设备,这里是从 HonHaiPr_54:d5:3d的MAC地址发送到Tp-LinkT_06:67:7d 路由器的MAC地址。
第三个目录Internet Protocol Version 4, Src: 10.1.1.64, Dst: 192.168.122.217
下的目录Destination GeoIP: CN
[Destination GeoIP: CN] [Destination GeoIP Country: China] [Source or Destination GeoIP Country: China] [Destination GeoIP ISO Two Letter Country Code: CN] [Source or Destination GeoIP ISO Two Letter Country Code: CN] [Destination GeoIP Latitude: 34.7725] [Source or Destination GeoIP Latitude: 34.7725] [Destination GeoIP Longitude: 113.7266] [Source or Destination GeoIP Longitude: 113.7266]
GeoIP是基于IP查询地理位置。
找到UDP首部目录User Datagram Protocol, Src Port: 8801, Dst Port: 8800
User Datagram Protocol, Src Port: 8801, Dst Port: 8800 Source Port: 8801 Destination Port: 8800 Length: 41 Checksum: 0x16bc incorrect, should be 0x7c26 (maybe caused by "UDP checksum offload"?) [Expert Info (Error/Checksum): Bad checksum [should be 0x7c26]] [Bad checksum [should be 0x7c26]] [Severity level: Error] [Group: Checksum] [Calculated Checksum: 0x7c26] [Checksum Status: Bad] [Stream index: 0]
依次看到RFC 768定义的UDP首部,Source Port、Destination Port、Length、Checksum的信息。可以看到checksum错误,获取的包的checksum与计算出来的checksum不一致。这是因为有些路由器会参与checksum的计算,但上层协议栈并不知情,所以二者算出的checksum值不一样。
检验和计算可能由网络网络驱动,协议驱动,甚至是硬件完成。高层校验通常是由协议执行,并将完成后的包转交给硬件。比较新的网络硬件可以执行一些高级功能,如IP检验和计算,这被称为checksum offloading。网络驱动不会计算校验和,只是简单将校验和字段留空或填入无效信息,交给硬件计算。
注:本文为小yip原创,未经许可不得在任何平台转载。如需转载,与作者联系~
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