centos7 突然外网不通解决方案（持续更新）

今天centos服务器无故抽风，真的是无故！！突然就这样子了

yum -y update
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was
14: curl#7 - "Failed to connect to 2001:1b48:203::4:10: 网络不可达"

 One of the configured repositories failed (未知),
 and yum doesn't have enough cached data to continue. At this point the only
 safe thing yum can do is fail. There are a few ways to work "fix" this:

     1. Contact the upstream for the repository and get them to fix the problem.

     2. Reconfigure the baseurl/etc. for the repository, to point to a working
        upstream. This is most often useful if you are using a newer
        distribution release than is supported by the repository (and the
        packages for the previous distribution release still work).

     3. Run the command with the repository temporarily disabled
            yum --disablerepo= ...

     4. Disable the repository permanently, so yum won't use it by default. Yum
        will then just ignore the repository until you permanently enable it
        again or use --enablerepo for temporary usage:

            yum-config-manager --disable
        or
            subscription-manager repos --disable=

     5. Configure the failing repository to be skipped, if it is unavailable.
        Note that yum will try to contact the repo. when it runs most commands,
        so will have to try and fail each time (and thus. yum will be be much
        slower). If it is a very temporary problem though, this is often a nice
        compromise:

            yum-config-manager --save --setopt=.skip_if_unavailable=true

Cannot find a valid baseurl for repo: base/7/x86_64
 

初步判断是网络异常，ping一下，内部网络通，别的服务器ping这台也是通的；但是ping外部网络不通。

查询网络配置，一切都是OK的。

将网卡物理地址加入网卡配置信息，未解决。

[root@master ~]# vi  /etc/yum/pluginconf.d/fastestmirror.conf
[root@master ~]# vi /etc/yum.conf
[root@master ~]# vi /etc/resolv.conf

更改这些文件配置，未解决

百度！各站点没有一个靠谱的说法，仍继续解决中（有小伙伴有解决办法还请留言哦）