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Harun Baris Bulut
Asked: 2014-03-24 03:36:27 +0800 CST

Centos randomly stops communication with public internet

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When I try to install cPanel on fresh CentOS 6.5, it starts perfectly fine. It downloads packages and installs etc, and then it stops the install at a point. CentOS also cannot ping public internet, however it can ping local servers through public and private interfaces.

Edit; Server is behind NAT.

Symptoms are;

  • I cannot ping public network (anything in the internet)
  • I cannot ping gateway
  • I can ping local servers through local interface
  • I can ping public IPs of local servers through public interface
  • I can still connect to SSH from its public and private interfaces
  • I have remove iptables rules but it didnt helped.
  • I have changed keep alive options from sysctl.conf but it didnt help
  • I can only ping again the internet when I restart the machine

Edit; Restarting network worked this time.

Edit 2; I have made changes on tcp_keep_alive options and changed like this;

net.ipv4.tcp_keepalive_time = 86400
net.ipv4.tcp_keepalive_intvl = 75
net.ipv4.tcp_keepalive_probes = 20

These changes made the connection a bit better, what is happening right now is server still losts its connection but reconnects to network in a very short time.

Do you have any ideas about what is happening ?

I am a bit desperate right now :(

Thanks in advance

linux

1 Answers

  1. I would do the following

    1) check default gateway

    2) check DNS (resolve)

    3) turn of server, and try to ping the ip of this host, to make sure no duplicate ip

    4) print out dmsg and syslog after network goes from working to not working, look for cronjob set to do something at boot.

    5) you seem to have several network cards on many servers, make sure your network does not have a loop. does other servers have any problems? are both network cards accidentally on same vlan or on same dumb switch?

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