主机网络ping: unknown host baidu.com问题解决

时间：2021-05-16 05:22:26

本机环境：

系统：Centos 网络：NAT

虚拟机之前一直都可以连外网，但最近不能连了，现状如下：

[root@vhost03 ~]# ping baidu.com
ping: unknown host baidu.com

查看了下本机的网卡配置：

[root@vhost03 ~]# more /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE="eth0"

BOOTPROTO="static"

HWADDR="00:0C:29:D7:D2:49"

IPV6INIT="yes"

NM_CONTROLLED="yes"

ONBOOT="yes"

TYPE="Ethernet"

UUID="f08dcf57-d670-46b3-8298-240cd0b76bc2"

IPADDR=192.168.196.129

BROADCAST=192.168.196.255

NETMASK=255.255.255.0

GATEWAY=192.168.1.1

新装的虚拟机默认都是dhcp方式获取IP。为了保证IP固定，自己更新了网卡信息，使用了static模式。其中最后四行是按照dhcp模式时，使用ifconfig命令获取的信息。

查看DNS信息：

[root@vhost03 ~]# more /etc/resolv.conf

# Generated by NetworkManager

# No nameservers found; try putting DNS servers into your

# ifcfg files in /etc/sysconfig/network-scripts like so:

#

# DNS1=xxx.xxx.xxx.xxx

# DNS2=xxx.xxx.xxx.xxx

# DOMAIN=lab.foo.com bar.foo.com

上述结果表示并没有配置DNS。

正确的解决方式：

[root@vhost03 ~]# cd /etc/sysconfig/network-scripts/

[root@vhost03 network-scripts]# cp ifcfg-eth0 ifcfg-eth0.bak

[root@vhost03 network-scripts]# vi ifcfg-eth0

DEVICE="eth0"

BOOTPROTO="dhcp"

HWADDR="00:0C:29:D7:D2:49"

IPV6INIT="yes"

NM_CONTROLLED="yes"

ONBOOT="yes"

TYPE="Ethernet"

[root@vhost03 Desktop]# service network restart

[root@vhost03 Desktop]# ifconfig

eth0      Link encap:Ethernet  HWaddr :0C::D7:D2:

          inet addr:192.168.196.135  Bcast:192.168.196.255  Mask:255.255.255.0

          inet6 addr: fe80::20c:29ff:fed7:d249/ Scope:Link

          UP BROADCAST RUNNING MULTICAST  MTU:  Metric:

          RX packets: errors: dropped: overruns: frame:

          TX packets: errors: dropped: overruns: carrier:

          collisions: txqueuelen:

          RX bytes: (140.3 MiB)  TX bytes: (3.4 MiB)

lo        Link encap:Local Loopback

          inet addr:127.0.0.1  Mask:255.0.0.0

          inet6 addr: ::/ Scope:Host

          UP LOOPBACK RUNNING  MTU:  Metric:

          RX packets: errors: dropped: overruns: frame:

          TX packets: errors: dropped: overruns: carrier:

          collisions: txqueuelen:

          RX bytes: (1.0 KiB)  TX bytes: (1.0 KiB)

[root@vhost02 ~]#  netstat -rn

Kernel IP routing table

Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface

192.168.196.0   0.0.0.0         255.255.255.0   U                     eth0

169.254.0.0     0.0.0.0         255.255.0.0     U                     eth0

0.0.0.0         192.168.196.2   0.0.0.0         UG                    eth0

[root@vhost03 Desktop]# more /etc/resolv.conf

# Generated by NetworkManager

domain localdomain

search localdomain

nameserver 192.168.196.2

根据上面的信息重新配置ifcfg-eth0文件

[root@vhost03 ~]# cd /etc/sysconfig/network-scripts/

[root@vhost03 network-scripts]# vi ifcfg-eth0

DEVICE="eth0"

BOOTPROTO="static"

HWADDR="00:0C:29:D7:D2:49"

IPV6INIT="yes"

NM_CONTROLLED="yes"

ONBOOT="yes"

TYPE="Ethernet"

UUID="f08dcf57-d670-46b3-8298-240cd0b76bc2"

IPADDR=192.168.196.129

BROADCAST=192.168.196.255

NETMASK=255.255.255.0

GATEWAY=192.168.196.2

[root@vhost03 ~]# cd /etc/sysconfig/network-scripts/

[root@vhost03 network-scripts]# service network restart

[root@vhost03 network-scripts]# vi /etc/resolv.conf 

# Generated by NetworkManager

domain localdomain

search localdomain

nameserver 192.168.196.2

[root@vhost03 ~]# ping www.baidu.com

PING www.a.shifen.com (115.239.210.27) () bytes of data.

 bytes from 115.239.210.27: icmp_seq= ttl= time=6.46 ms

 bytes from 115.239.210.27: icmp_seq= ttl= time=7.00 ms

ok,问题解决。分析下来，看来是之前获取的历史网卡信息变了，导致不能ping外网。

之前有在其它网络环境下重启过宿主机，应该和这个有关。解决问题的时候发现，只要重启网卡就会出现/etc/resolv.conf 被重置的现象。这是因为

[root@vhost02 ~]# chkconfig --list |grep -i network
NetworkManager  0:off   1:off   2:on    3:on    4:on    5:on    6:off
network         0:off   1:off   2:on    3:on    4:on    5:on    6:off

[root@vhost02 ~]# service NetworkManager stop

NetworkManager进程会实时修改/etc/resolv.conf 中的信息

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