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Wired Networks Thread, Why would an entire building have 169 IPs but rest of the site is fine? in Technical; The Netgear switches are fine. The switches in the offending building are Planet FGSW 2402-rs. The lights are going crazy ...
  1. #16

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    The Netgear switches are fine. The switches in the offending building are Planet FGSW 2402-rs. The lights are going crazy and loading windows takes an age.... Broadcast storm?

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    jamesreedersmith's Avatar
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    Sounds like a broadcast storm - unplug all cables, reboot switches and gradually repatch until issue reappears, then resolve issue.

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    north-ict's Avatar
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    Quote Originally Posted by TomHD View Post
    Ok, so some machines now have a 10.xxx.xxx.xxx IP but have no internet access although windows is saying there is! I've plugged a Mac Book directly into the switches in the offending building and its gets a 10.xxx.xxx.xxx IP but no Internet again.

    I have tried assigning static IP to a machine in the building and pinged the DHCP but host was unreachable.

    Thanks for the replies so far
    Is that due to proxy settings not set up, [if you are using a proxy on site ???] (Ignore me if I am way off)

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    Just to clarify, on the Planet switches in the offending building I have solid amber lights and frantically flashing, in unison green lights. Broadcast storm?

    I will be coming in this weekend to carry out jamesreedersmith solution

  5. #20

    localzuk's Avatar
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    That sounds just like a broadcast storm, yeah.

  6. #21

    tmcd35's Avatar
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    Quote Originally Posted by TomHD View Post
    The Netgear switches are fine. The switches in the offending building are Planet FGSW 2402-rs. The lights are going crazy and loading windows takes an age.... Broadcast storm?
    99.99999999999995% certain of a broadcast storm. Most likely culprit is a student plugging a network cable between two network points - grrrr. Next most likely is a faulty NIC sending out bad packets. Easiest way to find out were (assuming points are labelled and correctly) is to unplug cables until the lights calm down. The last one unplugged before the lights stopped going crazy is your culprit!

    Also, thank the Edu Gods that you have spanning tree enabled otherwise your entire network would have been down!

  7. #22

    Dos_Box's Avatar
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    Planet FGSW 2402-rs? Seriously? Someone put in budget 10/100 switches?
    It may even be a capacity issue. I'd definately look at swapping out one of those to test whether it may be a bandwidth problem or simply rubbish hardware.

    Last edited by Dos_Box; 5th September 2014 at 04:20 PM.

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    Yeah, the rest of the hardware throughout is good stuff. Thanks for letting me know Planet are budget crap, I'll get and replace them next budget

    There is no labelling so that will be my first job in the morning. I will then unplug, power down, power up and plug 1 by 1.

    Funnily the caretaker knew exactly what I was talking about as he has heard of it happening in other schools!

    Thanks for all your help guys, I will be back with good or bad news tomorrow

  9. #24

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    So some further investigation has revealed that the offending building is served by a 48F SFP Link in the server room (on a Netgear GS748T) to another GS748T. This other GS748T then serves the Planet switches upstairs. If I remove the link between the Planet switches and the GS748T downstairs the storm stops on the Planet switches, it continues on the GS748T downstairs. If I then remove the link to the GS748T downstairs from the GS748T in the server room the storm stops on the one downstairs.

    Does this mean that the offender is connected to the GS748T switch in the server room?

    Many Thanks, Tom.

  10. #25

    Dos_Box's Avatar
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    I would try disconnecting all ethernet cables from the remaining switch in the server room one by one to see if the storm orginates from there (I take it the switch in the other building it links to is fine?). If you are still getting a storm in that switch, but not the one at the other end then try doing a hrd reset i.e. disconnect from mains and repower. If the storm still remains try swapping over the GBIC modules to check that you don't have a faulty one.
    If you have access to teh switch WEBMIN you can check which port is generating the most traffic.
    Also try adjusting the GBIC duplex options if they are available (if the problem is there of course).
    Just to suggest a few options of course.
    At least you are narrowing this down and I hope you get to the bottom of the problem today

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    Right, thanks for the responses guys. I have isolated some non working Ethernet ports and got the building back up and running as it should. I still worry there is an issue and the problem might crop up again. As its working and its Saturday I'm going home Fingers crossed all is well on Monday!

    Thanks again to all those involved

    Best and hoping all have a good weekend. Tom.

  12. #27

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    I have posted this elsewhere but it may be relevant.
    Apart from the "possibility" of the infamous malicious loop cable which is my own experience rare, there are dozens of other possibilities to cause this.

    Firstly do a packet capture using an analyser, wireshark will do to identify the source of the broadcast or multicast.

    The Multicasting issue has been around for sometime but in recent weeks probably related to many new roll outs or system image deployments PC's with Intel LAN cards can begin to multicast when in standby.
    This is intermittent and cause by a bug in the hardware and certain drivers.
    If your switches are not set to handle Multicast Packets you can loose complete sections of your LAN.
    Make sure you have IGMP Snooping configured correctly. Update any machine using Intel Lan cards to the latest drivers do not use the OEM or Windows own drivers.
    We arrived at a site with a similar condition during the break, they couldn't login or get an IP address.
    They were the only machine actually on at the time but the switches in this building section were going ape!
    A quick check on the Netgear switch web management identified 3 ports generating millions of multicast packets.
    The offending machines were brand new HP's that had been deployed using the same WDS image and they were all in standby!

    As soon as they were woken up or the switch reset the multicasting stopped.
    Updated the driver including the one in the image being deployed and the issue stopped.

    Other causes include, bad cabling, poor punch downs, twisted/damaged patch leads.
    These can easily cause excessive broadcast and switch issues if a single pair becomes open/short/intermittent.
    All 8 wires are needed for gigabit if one is broken or short the machines can suddenly drop out to 10/100 or loose the RX link completely effectively becoming deaf temporarily.
    They begin to broadcast frantically and as they are deaf don't know when to shut up!
    Once again better quality switches with broadcast storm controls can minimise these types of issues.

    Just because a switch is cheap is not enough to condemn the entire brand, especially as we don't know if the rest of your LAN is in good health!
    (Although I too would tend to avoid using Planet Switches on a Campus LAN).

    I was in a brand new building in Docklands yesterday, there was an argument going on between a BT engineer and a cabling contractor because an emergency phone wasn't working in a lift.
    Mr BT came into the Comms room and plugged in his handset, got dial tone. Went to lift no dialtone!
    Cable guy said it can't be his cabling as they were all tested and certified!
    But the Building Inspector guy said - No emergency phone no building opening - that was it.

    With nobody else equipped I offered the cable guy a terminator from my Fluke Test kit and asked him to plug it in the lift shaft RJ45 port.
    I immediately got a Pin 1 Or/Wh open circuit at his end.
    There you go I said, you will need to re-punch that outlet...
    Sod that he said, just move the patch cord to the next port in the patch panel.. hey presto it all worked!

    When he came to return my terminator I said what about the one wire that needs re-terminating? Not my problem he said...
    I counted well over 1000 RJ45 outlets there, how many more will there be in that brand new building incomplete?

    You will never be able to trust your cabling until you have verified each outlet yourself, do not write off the switchgear until you are certain your cabling is good.



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