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I have a Ubuntu box in my network which crashed, all the system connected to the switch in which the Ubuntu system was connected started giving problem. I removed that system from the network, since that was the last change I made in my network and everything was fine. So, to confirm this I again connected the system back to the network and the same network outage happened.

When I checked the links it was fine. When I rebooted the problematic system and again connected back to the network switch everything started working.

I think possibly the crash of the Ubuntu system could have caused this outage.

Is there any possibility that a kernel crash can cause network issues?

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Can you give us some details about the functions of your Unbutu box? DHCP? Dns? Samba? Nfs? Router? Basically some kernels crashes let your NIC up, even answering to pings, but the services just hang.. Also can you be more specific about "all the system connected to the same switch [..] started giving problem" ? –  Olivier S Nov 25 '11 at 6:04
    
The Ubuntu box is running 10.4 LTS, it is a newly setup clean system with SSH and a Dovecot service installed. I was running 1K processes which were copying files within the system. The server load was very high "load average: 1001.47 1001.43 995.18". I understand that the crash could be due to this, but how it can cause network issue? –  Supratik Nov 25 '11 at 6:34
    
I have few simple switches which in turn connect to a router. All systems are connected to these switches. The Ubuntu system was connected to one of the switch and all the system connected in that switch was not able to connect to the network. I believe its due to malformed packets from the Ubuntu system but not sure if it is possible. –  Supratik Nov 25 '11 at 6:34

2 Answers 2

There are a lot of ways. If the machine started spewing broadcast packets and the switch doesn't have broadcast rate-limiting, that would do it. If the machine started responding to DHCP requests, that would do it. If the machine assigned itself the same IP address as your router, that would do it.

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No, a system crash should not cause network problems in the traditional sense.

However, it's possible that you somehow got the switch involved. If you're using dumb cheap switches, it's very well possible to crash it with an misbehaving system: Back in the days, I could crash various switches by just creating a huge amount of TCP sessions. Cheap switches often don't handle an full address table very well.

Just shell out a few bucks more, and buy an established brand.

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