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Wireless Networks Thread, 3Com Switches Re-setting at random around the school in Technical; I have about 25 switches around the high school. Mainley 48 port 3com. At random around the school they are ...
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    3Com Switches Re-setting at random around the school

    I have about 25 switches around the high school. Mainley 48 port 3com. At random around the school they are re-setting. They come back up alright but the end users get the message that the network has gone! Does anybody have any ideas?

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    Re: 3Com Switches Re-setting at random around the school

    Removed.

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    Re: 3Com Switches Re-setting at random around the school

    Would they not need to know the ip address of the switch to do this?

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    Re: 3Com Switches Re-setting at random around the school

    Sounds like you're talking about SMBDie or one of the similar apps which unpatched XP is vulnerable to. Either way it's not really something a switch would be affected by.

    Re-configured the switches at all recently (I assume they're at least L2 managed)? A quick google comes up with this - not sure if that could be related.

    Is there a newer firmware available for the switch? Did it only start happening recently?

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    Re: 3Com Switches Re-setting at random around the school

    It has been doing it randomley since they were put in 14 months ago. I have been on the web and there is no firmware upgrade for this model??

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    Re: 3Com Switches Re-setting at random around the school

    Might be a power problem. Try putting your most troublesome switch on UPS. Make sure you monitor the switch and the UPS for network/power issues.

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    Re: 3Com Switches Re-setting at random around the school

    Thanks geoff, i thought this. We have a ups on a few of the switches and this has not made any difference. We have also had an electrical contractor out to access the electrics.

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    Re: 3Com Switches Re-setting at random around the school

    Realy stupid question. are they all password protected?

    If im not mistaken im sure you can do a restart via web

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    Re: 3Com Switches Re-setting at random around the school

    Quote Originally Posted by bishopsgarthstockton
    Realy stupid question. are they all password protected?

    If im not mistaken im sure you can do a restart via web
    Yes they are password protected -

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    Re: 3Com Switches Re-setting at random around the school

    Re-address a couple to something not on your usual network range temporarily, or disable network management totally for a while (as long as you keep a console cable + laptop handy of course).

    You'd at least know whether it was an exploit / someone with the password etc etc, or just faulty hardware / power / whatever then.

    Are you sure the switch is actually rebooting and it's not just some issue with auto negotiation? Some switches do have issues with some NICs and will be forever trying to re-negotiate a link speed / duplex.

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    Re: 3Com Switches Re-setting at random around the school

    If they were clever enough a port scan would bring up the right reults for the characteristics of a switch eg telnet port and a web port so I wouldnt have said just changing the IP address would work. You can even get those nice handy apps from the manufacturer that scan by mac address for that particular manufacturer.
    Are you definately sure they are resetting and that you arent suffering some kind of broadcast storm (is spanning tree protocol enabled to help protect you from this?)

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    Re: 3Com Switches Re-setting at random around the school

    Quote Originally Posted by GeeDee
    Re-address a couple to something not on your usual network range temporarily, or disable network management totally for a while (as long as you keep a console cable + laptop handy of course).

    You'd at least know whether it was an exploit / someone with the password etc etc, or just faulty hardware / power / whatever then.

    Are you sure the switch is actually rebooting and it's not just some issue with auto negotiation? Some switches do have issues with some NICs and will be forever trying to re-negotiate a link speed / duplex.
    In the maagement it says the up time. for example 4 switches in 1 cabinet 3 of them would have been up for 100 days and yet this 1 would have only been up for 20 mins. i only look when someone calls to say the network has gone for a few seconds. i cannot really disable the management as there are vlans on all the switches. when the school is closed the swtiches never reset. i have tried to tell the network manager that is must be 1 unit that is attached somewhere but he disagrees. if i was to try and find a source for the problem does anyone know of a peice of software that would help me??

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    Re: 3Com Switches Re-setting at random around the school

    Quote Originally Posted by ChrisH
    If they were clever enough a port scan would bring up the right reults for the characteristics of a switch eg telnet port and a web port so I wouldnt have said just changing the IP address would work. You can even get those nice handy apps from the manufacturer that scan by mac address for that particular manufacturer.
    Are you definately sure they are resetting and that you arent suffering some kind of broadcast storm (is spanning tree protocol enabled to help protect you from this?)
    I am not sure if spanning tree is disabled as i got told by 3com to disable spanning tree?? I will check. Do you think this would help?

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    Re: 3Com Switches Re-setting at random around the school

    If you disable STP you have no protection from network loops and thus ARP storms. This will lock up switches to varying degrees depending on the backplane bandwidth of the switches.

    If you want some switch monitoring software consider Nagios or Cacti.

    http://nagios.org/
    http://cacti.net/

    Nagios will give a real time over view of your network where as Cacti will tell you about the historic performance of devices over time. They both require snmp capable devices to work. You'll also need a Linux web server to run them on as they are LAMP apps.

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    Re: 3Com Switches Re-setting at random around the school

    Quote Originally Posted by western
    In the maagement it says the up time. for example 4 switches in 1 cabinet 3 of them would have been up for 100 days and yet this 1 would have only been up for 20 mins.
    Ok, so clearly a switch issue then. Could be hardware or software however.

    Quote Originally Posted by western
    i cannot really disable the management as there are vlans on all the switches. when the school is closed the swtiches never reset.
    No, you can't disable management but you can re-address a couple of units to an off net address of your choice (10.10.10.1/24 or whatever). Vlans are only L2, so the IP assigned to the switch is purely for management. I assume you're not doing L3 routing on 25 switches.

    You can then either temporarily switch (or alias) a random machine to the 10.10.10.0 network or console the switch directly when (if) you need to manage it. If the switch never falls over, then it's most likely either some vulnerability in the 3com magement software, or someone with the password resetting via the webmin, or some other happening on the LAN. You can then investigate the problem before re-config'ing the switch management back to your usual network.

    The only other likely cause would be faulty hardware. What's the warranty? It seems unlikely that broadcast storms or network loops would cause a switch to crash and reboot itself, especially while the rest of the LAN continues to run happily.



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