I have been searching the internet for a few days now for a solution to this problem and I have found no solution yet.

I just installed Ubuntu 14.04.3 on a server and my server sporadically and selectively stops responding to pings, drops all connected sessions and stop accepting web server requests. I say selectively because I send pings from different machines and server responds to some and does not respond to the others at the same time. I believe it must be a security setting or firewall setting but I have not been able to find any solution to this issue. Please someone help me. Thanks

  • What does “disconnects ssh” and “stop accepting web server requests” mean exactly? How SSh sessions break down and what are symptoms of non-functioning HTTP? – Incnis Mrsi Aug 15 '15 at 11:59
  • What I mean is that I keep open ping sessions from 2-3 different machines on 2-3 different networks to the Ubuntu server and at some point, the server stops responding to one or two while still responding to the last one so I cannot ssh into the server from the "no-response" network since the server is "blocking" requests from that network. I believe it has something to do with some kind of security setting in Ubuntu but since I am new to Ubuntu, I have no clue.. – NogieUbuntu Aug 15 '15 at 13:38
  • Please, do not miss important details: are existing SSh sessions really disconnecting? Or the glitch only precludes new sessions from establishing? – Incnis Mrsi Aug 15 '15 at 13:42
  • I do not think that SSH sessions are really disconnecting just that the network disconnects hence no ssh access. – NogieUbuntu Aug 15 '15 at 13:44
  • Now edit the question, reword the confusing dis connecting  stuff, and provide more IP-level information. We don’t even know whether is it a local area network problem or a purely Internet one. – Incnis Mrsi Aug 15 '15 at 13:53

Since the original poster didn’t provide any network topology and addressing data, we can’t make even an educated guess whether is it

  • a firewall problem or
  • a network connectivity/routing problem (including erroneous routing table in the box in question).

In the former case the default Ubuntu firewall is UFW. Check its status with

sudo ufw status

and if it’s enabled, then turning logging on (see the wiki link above) might be helpful to continue with diagnostics. Even if UFW is inactive, some other firewall software may be present, so examining iptables would be a good idea.

In the latter case traceroute in both directions can find where the routing is broken.

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