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How to check for Network interface collision using Nagios

Posted on 2009-07-02
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Last Modified: 2012-06-27
Hey

I was hoping someone knows how to do this :)

We have a few production servers that is currently monitored by Nagios. But we ran into an situation where some clients had issues, after allot of searching and trouble shooting we found that the one connecting servers (Ubuntu 6 server) had collisions on its main Network Interfaces (ifconfig lists collisions at:12925212) , all the other servers collisions were sitting at 0. We believe the connection issue is due to the collisions on the network interface (My Manager is investigating how to fix it :P ).

But now I have the task to find away to monitor the network interfaces for collisions and if there is, an alert or notification needs to be sent.

Thus is there away to use Nagios to monitor a Linux Based machines Network Interface for Collisions specifically.

Thx
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Question by:Rigged
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I would have to check which one it is, but I am 99.9999% sure that there is a SNMP MIB that show collisions.

However, collisions can be normal. If you are connected to a hub (not a switch, but a old fashion hub) or you are connected to a switch and for some reason must operate in half duplex, then collisions are normal.  

However, if you are connected to a switch and can operate in full duplex, you should not see any collisions.  So, if you are connected to a switch, I would verify that the NIC and the switch port are both configured as either full duplex (preferred) or as duplex auto.  They both must be configured the same.

Auto duplex sometimes does not work, that is why I prefer to hard code for full duplex.  Some newer gigabit NIC's and switches do not  allow hard coding of full duplex.
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by:Rigged
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Cool thanks, I will check if I can find a SNMP check that can do that.

But in answer to your question about the duplexing. We did have an issue on the switch about 3 weeks ago that it put all the Servers connected to it onto Half-Duplex. We then ran ethtool on the servers for the affected NIC's and switched of the NIC's auto and forced it onto Full. The switch is a cisco switch and we didn't change the duplexing or the auto settings on it, mainly because we don't know how to. I will google quickly to see how to cahnge the Cisco switch interface duplexing settings.

Do you maybe know what the results could be for forcing the servers NIC's to a forced full duplex state while the switch is still on Auto, could it also cause connectivity issues or other network issues?
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Which Cisc switch is it?

All the ones I have used from the cli you can:

     enable
     config t
     int xx#/#
     duplex full

Where xx is the type of interface fa for fast ethernet and gi for gigabit Ethernet.  Yes, if one side is forced to a specific duplex and the other side is auto you could end up with a mis-match in duplex.  This is because the side that is forced will not do the duplex negotiation and so the auto side will default, and typically the default is half.
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