CentOS网络配置后无法访问外网的解决方法
<p style='margin: 0px; padding: 5px 0px; outline: none; font-size: 14px; line-height: 30px; font-family: tahoma, arial, "Microsoft YaHei";'>关于CentOS网络的具体配置项，可以参考Mitchell博客之前的那篇文章。</p>
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现象：</p>
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ping内网正常<br>
ping外网IP，域名均无法正常，返回错误：connect: Network is unreachable</p>
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后面在无意中看到Linux网络配置有添加网关的命令：</p>
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<span><u>复制代码</u></span>
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代码如下:</div>
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route add default gw 192.168.128.2 dev eth0 </div>
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按上面操作，添加了默认的网关之后。再次访问外网一切正常。</p>
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有这个现象来看，应该是配置文件中没有配置网关，但是经过确认/etc/sysconfig/network 中是配置了GATEWAY地址的，而且GATEWAY的地址也是正确的，在多次重启network之后，只要不手动添加网关，就不能访问外网。</p>
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多次仔细确认各个网络配置文件之后，发现在网卡配置文件中（ifcfg-eth0）有一个NETWORK配置项，对于这个配置项，本身作用不是很清楚，因此到官网查看了一下说明：</p>
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<span><u>复制代码</u></span>
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代码如下:</div>
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NETWORK=<address> <br>
where <address> is the network address. This directive is deprecated, as the value is calculated automatically with ifcalc.</div>
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这节奏是告诉我们这个参数不要设置嘛（deprecate），这个值将会由ifcalc自动计算。既然不用设置，自然去掉。</p>
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去掉之后，重启network服务之后，外网竟然神奇的能够访问了。使用route查看路由表，发现能够自动添加default这条信息了，原来可是一直没有的：</p>
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<span><u>复制代码</u></span>
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代码如下:</div>
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Kernel IP routing table <br>
Destination Gateway Genmask Flags Metric Ref Use Iface <br>
192.168.128.0 * 255.255.255.0 U 0 0 0 eth0 <br>
link-local * 255.255.0.0 U 1002 0 0 eth0 <br>
default 192.168.128.2 0.0.0.0 UG 0 0 0 eth0</div>
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看来问题正是这个NETWORK参数设置引起的。至于具体为什么会这样，这个设置会产生什么样的影响还不是很清楚。</p>
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TIPs：为了简单，你也可以将IPADDR，GATEWAY等设置到ifcfg-eth*的文件中，不用将GATEWAY单独设置在network中。</p>
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