Monthly Archives: January 2023

Golang 中网络请求使用指定网卡

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当用户发起一个网络请求时，流量会通过默认的网卡接口流出与流入，但有时需要将流量通过指定的网卡进行流出流入，这时我们可能需要进行一些额外的开发工作，对其实现主要用到了 Dialer.Control 配置项。

type Dialer struct {
​
    // If Control is not nil, it is called after creating the network
    // connection but before actually dialing.
    //
    // Network and address parameters passed to Control method are not
    // necessarily the ones passed to Dial. For example, passing "tcp" to Dial
    // will cause the Control function to be called with "tcp4" or "tcp6".
    Control func(network, address string, c syscall.RawConn) error
}

可以看到这是一个函数类型的参数。

环境

当前系统一共两个网卡 ens33和 ens160 ，ip地址分别为 192.168.3.80 和 192.168.3.48

➜  ~ ifconfig
ens33: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.3.80  netmask 255.255.255.0  broadcast 192.168.3.255
        inet6 fe80::8091:2406:c51e:ecb9  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:4f:05:90  txqueuelen 1000  (Ethernet)
        RX packets 4805008  bytes 826619853 (826.6 MB)
        RX errors 0  dropped 104152  overruns 0  frame 0
        TX packets 732513  bytes 284605386 (284.6 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
​
ens160: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.3.48  netmask 255.255.255.0  broadcast 192.168.3.255
        inet6 fe80::259a:d8d4:80a9:7fa4  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:4f:05:9a  txqueuelen 1000  (Ethernet)
        RX packets 4158530  bytes 746167179 (746.1 MB)
        RX errors 1  dropped 106875  overruns 0  frame 0
        TX packets 351616  bytes 149235606 (149.2 MB)
        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 426742  bytes 80978543 (80.9 MB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 426742  bytes 80978543 (80.9 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
​

路由表记录

➜  ~ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.3.1     0.0.0.0         UG    100    0        0 ens33
0.0.0.0         192.168.3.1     0.0.0.0         UG    101    0        0 ens160
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 ens33
192.168.3.0     0.0.0.0         255.255.255.0   U     100    0        0 ens33
192.168.3.0     0.0.0.0         255.255.255.0   U     101    0        0 ens160
​

从最后两条路由记录可以看到对于 192.168.3.0/24 这个段的流量会匹配的两个物理网卡，但由于配置的 Metric 的优先级比较的高，因此最终流量只会走网卡 ens33。

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