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Wireless Networks Thread, Complete loss of all network!!! in Technical; Just had a complete loss of all network due to what looked like a loopback at first. Looked at our ...
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    Complete loss of all network!!!

    Just had a complete loss of all network due to what looked like a loopback at first. Looked at our DES-6500 stack and we had 100% utilization so proceeded to unplug each fibre plug one by one until we found out what room was the problem.

    Reset our router and with that room unplugged everything else worked fine.
    After investigation in that room we couldn't find any loopbacks or any obvious problems.
    Connected it back up and reset all the computers and the switch in that room and now everything works fine.
    Could be a problem with that module in the DES-6500 because one of the link lights wasn't lighting up when plugged into a particular port but worked on another port.

    Any ideas anyone?

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    mac_shinobi's Avatar
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    Dead network card in one of the machines ?

    Long shot but could be a dead NIC in one of the machines ?

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    Its more likely to be a switch getting on its last legs. Check to see if a cooling fan on the switchs are ok. They overheat.

    richard

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    Quote Originally Posted by gecko View Post
    Long shot but could be a dead NIC in one of the machines ?
    Seen the above cause similar problems. Also seen a flakey fibre transciever do similar.

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    TechMonkey's Avatar
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    Yep same for a dodgy NIC. Had that on our network and it was fun finding. I have also seen a loop back created and the problems persist until the router was reset. Is is possible that some kids created a loopback and then removed it?

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    Quote Originally Posted by TechMonkey View Post
    Yep same for a dodgy NIC. Had that on our network and it was fun finding. I have also seen a loop back created and the problems persist until the router was reset. Is is possible that some kids created a loopback and then removed it?
    The possibility is there. There was a class of what looked like naughty kids in the room affected. Getting the teacher to shout at them didn't make any of them own up though lol. We have also had dodgey NIC's but I think this points more towards the switch/fibre module. We have a new module on order just in case anyway.

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    We've eliminated most loop-back problems with a config change on our switches. Whether or not you can do this depends on your switches, ours are HP Procurve.

    Instead of the default setting of autoconnect on the switch ports, that allows the switch to decide what type of device is being plugged in, we changed them to only allow slave devices to be connected, ie. PCs, Printers etc... but not other switches. Now if a cable is looped the switch doesn't make the connection to itself and there's no problem.

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    zag
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    Just out of interest is there a way to stop loopbacks at the router level? I only patch one port usually on the dual ones to stop loopbacks occurring but it would be better to have some intelligence in the switch to stop it bringing down the whole network.

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    Geoff's Avatar
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    Use Spanning Tree.

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    Spanning tree ?

    Quote Originally Posted by Geoff View Post
    Use Spanning Tree.
    Does that really work?

    Are there any requirements for getting it to work correctly or does it cause more headaches ?

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    DMcCoy's Avatar
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    Quote Originally Posted by gecko View Post
    Does that really work?

    Are there any requirements for getting it to work correctly or does it cause more headaches ?
    Yes, it works.

    There are different types of spanning tree, and often you need to configure ports to reduce the time delay introduced when plugging devices in. I think it's about 2 seconds delay when set correctly here, but I've seen 30 seconds when I chose the wrong option.

    I tend to use RSTP on all my edge switches, with MSTP running on the core. MSTP has other uses when dealing with redundancy but that get a little more complicated and a expensive.

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    localzuk's Avatar
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    We replaced our aging DES-6500 as it was doing similar random things. We now have a HP 5406zl instead.

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    Just had a look at a brand new switch (DES-3550) we have and there is an option for "Loopback Detection". Here is a screenshot:



    Any ideas on what settings should be used?

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    On The DES-6500 we stopped loop back by putting on Flow control on the ports, also doing the same on our switches in the IT suites (DGS 3024)

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    Quote Originally Posted by TronXP View Post
    On The DES-6500 we stopped loop back by putting on Flow control on the ports, also doing the same on our switches in the IT suites (DGS 3024)
    We had an issue with Flow Control knocking out our Internet Connection. Our router to the outside world is a Cisco 2950 managed by our provider. One of the switches had Flow Control switched on a number of ports and this was causing the Cisco Port to 'trip out'. Had me banging my head against the wall for a while, but when I switched flow control off all the problems went away.

    Pete

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