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582 Views 8 Replies Latest reply: Apr 18, 2012 7:51 AM by Nilesh W RSS

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Network issue

Apr 9, 2012 6:55 AM

Nilesh W 254 posts since
Feb 20, 2009

Hi all,

 

I was facing network issues last week due to One PC.Network went down just because of  one PC.

 

After disconnecting PC, network got stable.I dont know why this PC hamper the network.

 

Can anybody please let me know what precaution or configuration need to be done on switches so that this type of issue will not come again.

 

Thanks in advance.

 

Nilesh

  • CiscoLoco - CCNP 956 posts since
    Feb 11, 2009
    Currently Being Moderated
    1. Apr 9, 2012 11:48 AM (in response to Nilesh W)
    Re: Network issue

    You could look into broadcast storm control to limit the broadcast packets the host can send into your network.

     

    ex. storm-control broadcast level 10.00

  • macd 21 posts since
    Feb 2, 2011
    Currently Being Moderated
    2. Apr 9, 2012 10:49 AM (in response to Nilesh W)
    Re: Network issue

    sounds like that PC was/is infected by a root kit which might be generating a lot of traffic. Storm control and making sure the port never forms a trunk might be helpfull options

  • Alex Kieser 79 posts since
    Jan 29, 2011
    Currently Being Moderated
    4. Apr 13, 2012 12:49 PM (in response to Nilesh W)
    Re: Network issue

    You'd want to look at errdisable and recovery states if someone calls you saying port is disabled you can check the recovery to see if it disabled the port because of the violation.

  • Jared 5,498 posts since
    Jul 27, 2008
    Currently Being Moderated
    5. Apr 13, 2012 1:05 PM (in response to Nilesh W)
    Re: Network issue

    Actually, what I would do is I would stick the PC on a stand alone hub that is completely isolated and not plugged into anything and then sniff the traffic as to what it is doing.  As macd stated, it could be an infected PC or it could be that it was running an app that would have similar affects on network traffic.  I have seen PC's intentionally running various Hacking tools that also would bring the network to a crawl.  You'd have to check out the PC or sniff the traffic or even both to find out the why behind the behavior.

  • Jimmy Sands 644 posts since
    May 7, 2009
    Currently Being Moderated
    7. Apr 18, 2012 7:28 AM (in response to Nilesh W)
    Re: Network issue

    Alot of things could cause this, once I found a malfunctioning NIC broadcasting frames out at too high a rate

     

    I was called out to a site, intermittent internet, 2 hours later, packet sniffer showed me one IP that was sending out 800 SSDP ackets per second, traced MAC down, disconnected PC, network stabilized.    Sniffer showed nothing out of ordinary, plugged PC back in, network went crazy again, returned NIC.  It was hooked up to an unmangaged switch and that uplinked to an extreme switch.

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