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One of our Linux (CentOS 7.5) servers got unreachable sometimes.

The only solution what i have is systemctl restart network.
And I found the fact that I could not ping any outside hosts and vice versa.

So I replaced the server with new server to solve this problem but i got the same problem on new server. (But another interface for our private network always reachable.)

network detail:

$ ifconfig
docker0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        inet 172.17.0.1  netmask 255.255.0.0  broadcast 172.17.255.255
        inet6                          prefixlen 64  scopeid 0x20<link>
        ether                    txqueuelen 0  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 8  bytes 656 (656.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

em1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet xxx.xxx.178.235  netmask 255.255.255.192  broadcast xxx.xxx.178.255
        inet6                            prefixlen 64  scopeid 0x20<link>
        ether                    txqueuelen 1000  (Ethernet)
        RX packets 36757565  bytes 32443194055 (30.2 GiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 38804620  bytes 32581348506 (30.3 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 53  

em2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.11  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6                            prefixlen 64  scopeid 0x20<link>
        ether                    txqueuelen 1000  (Ethernet)
        RX packets 4123332  bytes 1311703055 (1.2 GiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 3546248  bytes 510328190 (486.6 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 54 

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 69896787  bytes 31178480745 (29.0 GiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 69896787  bytes 31178480745 (29.0 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

System logs are surprisingly clear.

Any log files seem to indicate no error except for errors due to network stopped.
Please let me know the best steps to find out problem. I have no clue anymore.

  • Maybe it's not the server but your infrastructure? If the same thing happens to two different servers, I'd get massively suspicious about anything connected, i.e. switches, routers, cables, etc. – Lenniey Jan 10 at 8:07
  • I thought the same thing first time, but it's weird that network came back with just a single command. My opinion could be wrong because i am a developer so I might not know the whole picture of our infrastructure. So i told our infra engineer the thing you said. Thanks for your comment. :) @Lenniey – 원치호 Jan 10 at 9:31

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