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PC上测试
Ubuntu 16.04 本身已经支持双网卡同时工作，使用route命令查看时可以看到，目前无线网卡和有线网卡已经同时在工作，其中wlp2s0是无线网卡，enxa44cc8f621d9是有线网卡。
tony@pc:~$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default localhost 0.0.0.0 UG 100 0 0 enxa44cc8f621d9
default localhost 0.0.0.0 UG 600 0 0 wlp2s0
link-local * 255.255.0.0 U 1000 0 0 wlp2s0
172.16.1.0 * 255.255.255.0 U 0 0 0 vmnet1
192.168.1.0 * 255.255.255.0 U 100 0 0 enxa44cc8f621d9
192.168.43.0 * 255.255.255.0 U 600 0 0 wlp2s0
192.168.212.0 * 255.255.255.0 U 0 0 0 vmnet8
tony@pc:~$ 前两个default是默认网关，实际连接的话，有线网卡网卡能上外网，无线网卡只是一个局域内网。由于有这一行，系统在能正常通过有线网卡访问外网的同时，也可以通过无线网卡访问192.168.43.0号段的局域内网。
192.168.43.0 * 255.255.255.0 U 600 0 0 wlp2s0做一个测试，其中baidu.com是外网，可以如下正常ping通。
tony@pc:~$ ping baidu.com
PING baidu.com (111.13.101.208) 56(84) bytes of data.
64 bytes from 111.13.101.208: icmp_seq=1 ttl=52 time=4.23 ms
64 bytes from 111.13.101.208: icmp_seq=2 ttl=52 time=3.75 ms
64 bytes from 111.13.101.208: icmp_seq=3 ttl=52 time=3.80 ms
64 bytes from 111.13.101.208: icmp_seq=4 ttl=52 time=4.38 ms
^C
--- baidu.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3005ms
rtt min/avg/max/mdev = 3.750/4.044/4.382/0.281 ms其中192.168.43.37是局域内网下的一个设备，同样可以ping通，如下。
tony@pc:~$ ping 192.168.43.37
PING 192.168.43.37 (192.168.43.37) 56(84) bytes of data.
64 bytes from 192.168.43.37: icmp_seq=1 ttl=64 time=468 ms
64 bytes from 192.168.43.37: icmp_seq=2 ttl=64 time=80.8 ms
64 bytes from 192.168.43.37: icmp_seq=3 ttl=64 time=204 ms
64 bytes from 192.168.43.37: icmp_seq=4 ttl=64 time=25.3 ms
64 bytes from 192.168.43.37: icmp_seq=5 ttl=64 time=45.0 ms
64 bytes from 192.168.43.37: icmp_seq=6 ttl=64 time=67.8 ms
^C
--- 192.168.43.37 ping statistics ---
6 packets transmitted, 6 received, 0% packet loss, time 5007ms
rtt min/avg/max/mdev = 25.310/148.657/468.156/153.996 ms
tony@pc:~$ NanoPC-T2 Linux 上测试
连接上WiFi和以太网后，route就自动配置好了，如下所示，且ping外网和内网时可同时使用。
pi@FriendlyELEC:~$ ifconfig
eth0 Link encap:Ethernet HWaddr ca:ef:1f:c4:4e:ce
inet addr:192.168.1.124 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::8e3b:4240:cd32:eea6/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2281 errors:0 dropped:0 overruns:0 frame:0
TX packets:781 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:462086 (462.0 KB) TX bytes:70968 (70.9 KB)
Interrupt:64 Base address:0x4000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:1297 errors:0 dropped:0 overruns:0 frame:0
TX packets:1297 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1
RX bytes:109194 (109.1 KB) TX bytes:109194 (109.1 KB)
wlan0 Link encap:Ethernet HWaddr b0:f1:ec:29:06:18
inet addr:192.168.43.53 Bcast:192.168.43.255 Mask:255.255.255.0
inet6 addr: fe80::20ff:6245:96eb:1993/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:112 errors:0 dropped:1264 overruns:0 frame:0
TX packets:522 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:18279 (18.2 KB) TX bytes:90094 (90.0 KB)
pi@FriendlyELEC:~$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default localhost 0.0.0.0 UG 100 0 0 eth0
default localhost 0.0.0.0 UG 600 0 0 wlan0
192.168.1.0 * 255.255.255.0 U 100 0 0 eth0
192.168.43.0 * 255.255.255.0 U 600 0 0 wlan0
pi@FriendlyELEC:~$ ping 192.168.43.85
PING 192.168.43.85 (192.168.43.85) 56(84) bytes of data.
64 bytes from 192.168.43.85: icmp_seq=1 ttl=64 time=87.4 ms
64 bytes from 192.168.43.85: icmp_seq=2 ttl=64 time=105 ms
64 bytes from 192.168.43.85: icmp_seq=3 ttl=64 time=27.0 ms
64 bytes from 192.168.43.85: icmp_seq=4 ttl=64 time=49.7 ms
64 bytes from 192.168.43.85: icmp_seq=5 ttl=64 time=95.5 ms
64 bytes from 192.168.43.85: icmp_seq=6 ttl=64 time=96.0 ms
64 bytes from 192.168.43.85: icmp_seq=7 ttl=64 time=17.3 ms
^C
--- 192.168.43.85 ping statistics ---
7 packets transmitted, 7 received, 0% packet loss, time 6003ms
rtt min/avg/max/mdev = 17.389/68.420/105.762/33.631 ms
pi@FriendlyELEC:~$ ^C
pi@FriendlyELEC:~$
pi@FriendlyELEC:~$
pi@FriendlyELEC:~$ ping 202.108.22.5
PING 202.108.22.5 (202.108.22.5) 56(84) bytes of data.
64 bytes from 202.108.22.5: icmp_seq=1 ttl=57 time=2.22 ms
64 bytes from 202.108.22.5: icmp_seq=2 ttl=57 time=1.97 ms
64 bytes from 202.108.22.5: icmp_seq=3 ttl=57 time=1.85 ms
64 bytes from 202.108.22.5: icmp_seq=4 ttl=57 time=2.29 ms
^C
--- 202.108.22.5 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3004ms
rtt min/avg/max/mdev = 1.856/2.086/2.296/0.182 ms
pi@FriendlyELEC:~$ localhost是什么意思？
使用busybox route查看，不再是localhost了，这个应该更准确一点，更清晰了，这样设置就对了。
pi@FriendlyELEC:~$ busybox route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default 192.168.1.1 0.0.0.0 UG 100 0 0 eth0
default 192.168.43.1 0.0.0.0 UG 600 0 0 wlan0
192.168.1.0 * 255.255.255.0 U 100 0 0 eth0
192.168.43.0 * 255.255.255.0 U 600 0 0 wlan0
pi@FriendlyELEC:~$