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Hardware Thread, School Networking Issue - Random disconnecting machines - Plea for help :) in Technical; Originally Posted by User3204 Aww man, the date is wrong on those switches, this used to wind me up on ...
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    Quote Originally Posted by User3204 View Post
    Aww man, the date is wrong on those switches, this used to wind me up on my old HP, Cisco ones, now that I have a standard switch make across the site, it was so much easier to make them all sync from my NTP server.



    What brand switch(es) do you have ?
    How old is the oldest ?
    They are 3com switches. Been here longer than i have and when i asked the council they couldn't give me an answer :|

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    Is there anything specific to look out for in wireshark?

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    Quote Originally Posted by tj2419 View Post
    They are 3com switches. Been here longer than i have and when i asked the council they couldn't give me an answer :|
    Not sure about the older menu driven comware versions, but newer comware is quite straightforward.
    what model?

    Quote Originally Posted by tj2419 View Post
    We do have a mitel IP phone system that maybe on a VLAN. We have never managed the phones so i will check on that tomorrow. If it is how could a VLAN be causing the issues?
    There could be a loop between the different vlans caused by a misconfiguration. Check with wireshark to see if you see any VoIP broadcasts on the other network.

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    Have you checked that you have not got a loop through on the network. this will broadcast packets and sometimes lose connectivity we had this problems as we didn't have spamming tree turned on

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    Quote Originally Posted by nathan3388 View Post
    Have you checked that you have not got a loop through on the network. this will broadcast packets and sometimes lose connectivity we had this problems as we didn't have spamming tree turned on
    How would we check for a loop through on the network? Spanning tree, is this turned on, on the core switch? Any draw backs from enabling it? Cheers

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    Quote Originally Posted by tj2419 View Post
    How would we check for a loop through on the network? Spanning tree, is this turned on, on the core switch? Any draw backs from enabling it? Cheers
    no - should be enabled on all - As you ignored me previous post I guess you don't use securus?

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    go around and check cabling we had a kid plug one network cable in one port then pluged it into another slowed the network right down

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    Quote Originally Posted by glennda View Post
    no - should be enabled on all - As you ignored me previous post I guess you don't use securus?
    Hi I replied to your post :s the third post on here :s but we don't use securus. I'll have a look at the switches this morning.

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    If it were a loop that hadn't been disabled by STP, wouldn't you expect slightly different symptoms such as performance degradation across the entire LAN as opposed to the sporadic loss of DHCP lease info?

    Have any clients with static IPs ever been affected?

    I've seen similar issues when a dulicate DHCP server was introduced to the network in the form of an AIO TFTP/DHCP/DNS utility. If you haven't yet done so, it's worth having a look at event log on your DHCP server and perhaps sniffing for evidence of a duplicate DHCP server.
    Last edited by meastaugh1; 13th June 2012 at 07:22 AM.

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    Microsoft Network Monitor - slightly easier to use than wireshark and not the same amount of overhead installing it - I've shifted to using it rather than wireshark.

    I've seen similar behaviour from a router / core switch / managed wireless controller having the same IP as another device on the network.

    If you have a CCTV / IPTV system I would strongly suggest that this is put on its own VLAN - your IP phones should be on their own VLAN too.

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    I think the fact these problems have been on-going and the council have chosen to supply and manage switches for the school, it is their responsibility to make sure everything works.

    Credit to Service Birmingham for example, but the few network people I have spoken to there and been very helpful and have resolved networking issues over the phone, but also coming to visit the school in person.

  12. Thanks to Michael from:

    eduabncs (13th June 2012)

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    If you enable spanning tree then you should make sure portfast or similar is turned on or you could see odd problems with boot up times or builds. Saying that your symptoms dont suggest a loopback more a routing / ip conflict / or broadcast issue.

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    Quote Originally Posted by User3204 View Post
    If there are no VLANs on the switches, then is there any other configuration on them ?
    You coult try wiping the config on them, it's usually something simple, I know with the HPs you just boot it up with port 1 connected to port 2.
    That's only the correct procedure on the 1800 series noddy switches. On proper procurves you hold in the clear button, press reset and then release clear when the light sequence stop changing. If you are reseting 1800 series switches you need to disconnect them from the rest of the network. I however would not reset them if there's a maintenance agreement in place.

    Are you able to connect to the switches via either a serial cable of telnet?

    EDIT: Have you got any BAD ADDRESS errors on your DHCP server. Do you definably have exclusions setup for everything with a static I.P. address.
    Last edited by K.C.Leblanc; 13th June 2012 at 10:28 AM.

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