linux 命令route add default dev eth0和route add default gw eth0的区别？[通俗易懂]

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本机以太网卡eth0的IP地址为手动配置：

网关IP地址为192.168.1.1/24

#ifconfig eth0 192.168.1.100 netmask 255.255.255.0

#route add default dev eth0

//默认路由，将去往未知网络的数据包全部从接口eth0发出去

测试结果为ping外网失败；

[root@localhost ~]# netstat -rn

Kernel IP routing table

Destination     Gateway         Genmask         Flags   MSS Window irtt Iface

192.168.1.0     0.0.0.0         255.255.255.0   U         0 0          0 eth0

0.0.0.0         0.0.0.0         0.0.0.0         U         0 0          0 eth0

[root@localhost ~]# ping
www.baidu.com
-c 5

PING
www.a.shifen.com
(61.135.169.105) 56(84) bytes of data.

From localhost (192.168.1.110) icmp_seq=2 Destination Host Unreachable

From localhost (192.168.1.110) icmp_seq=3 Destination Host Unreachable

From localhost (192.168.1.110) icmp_seq=4 Destination Host Unreachable

From localhost (192.168.1.110) icmp_seq=5 Destination Host Unreachable

—
www.a.shifen.com
ping statistics —

5 packets transmitted, 0 received, +4 errors, 100% packet loss, time 4001ms

pipe 3

但是，如果我不写默认路由出接口，而是直接下一跳，却可以ping通外网！

如下：

#route del default dev eth0

//删掉刚才配的静态路由

#route add default gw 192.168.1.1       //写默认路由的下一跳地址

现在ping外网却通了！

[root@localhost ~]# netstat -rn

Kernel IP routing table

Destination     Gateway         Genmask         Flags   MSS Window irtt Iface

192.168.1.0     0.0.0.0         255.255.255.0   U         0 0          0 eth0

0.0.0.0         192.168.1.1     0.0.0.0         UG        0 0          0 eth0

[root@localhost ~]# ping
www.baidu.com
-c 5

PING
www.a.shifen.com
(61.135.169.125) 56(84) bytes of data.

64 bytes from 61.135.169.125: icmp_req=1 ttl=51 time=305 ms

64 bytes from 61.135.169.125: icmp_req=2 ttl=51 time=145 ms

64 bytes from 61.135.169.125: icmp_req=3 ttl=51 time=98.3 ms

64 bytes from 61.135.169.125: icmp_req=4 ttl=51 time=75.5 ms

64 bytes from 61.135.169.125: icmp_req=5 ttl=51 time=342 ms

—
www.a.shifen.com
ping statistics —

5 packets transmitted, 5 received, 0% packet loss, time 4005ms

rtt min/avg/max/mdev = 75.570/193.664/342.982/109.636 ms

========================================================

那么为什么 route …dev eth0不行？而route …gw eth0却可以呢？

原理上这两条命令应该是等价的阿！