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Network access gone slow!

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  • 11-12-2008 2:00pm
    #1
    pablo21
    Registered Users Posts: 728 ✭✭✭


    Guys I have a network with predominatley XP pro machines on a domain. In the last couple of days access times for files and particularly email access through Outlook 2003 is rediculously slow. The PST files for the emails are located on the server. I've split the pst files by archiving as some of them were getting quiet large. I've also disabled Symantec Corporate on a couple of machines to see if that was causing things to slow down but it doesnt appear to be making any difference. Any idea's anyone? All help greatly appreciated. Things were fine up until monday or tuesday this week. I've also made sure AV is up to date and all windows are up to date. Help!!


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    #2
    _CreeD_
    Registered Users Posts: 4,148 ✭✭✭_CreeD_


    If you're not seeing any resource issues on the server run netstat on it to get some info on things like fragmented/dropped packets. Also on your own machine load up Wireshark and just run a quick scan, if you are experience a broadcast/multicast storm you will see a lot of those packets show up even on your normal 'unicast' setup. If that yields nothing see if any of your switches allow you to monitor traffic (Cisco calls it "SPAN" but most smart switches have similar features), mirror your trunk (switch-switch or if you only have one switch then the port that links to your server(s)) and setup a machine with wireshark attached to the monitoring port, look for any odd traffic patterns.
    If you have the resources you could also load up a Linux box with NTOP and plug it into the monitoring port, this will give you traffic information. It's included with a larger free security package I like called OSSIM (www.ossim.net) and since OSSIM comes in a very easy to use bootable install CD it might be a better option if you don't want to manually setup NTOP. OSSIM also includes a number of other security tools that might help pinpoint the issue, especially if it's malware related.


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    #3
    Snaga
    Registered Users Posts: 1,562 ✭✭✭Snaga


    Have you had a switch or server reboot recently?

    A primary cause of this kind of thing is an ethernet duplex mismatch, in this case possibly between your server switch and the rest of the access switches. Or else between your server and the switch port itself.

    If they are managed switches you should be able to get interface stats on your suspect ports to check for errors and should be easy to fix once found by matching settings on both switch ports (Or server and switch ports).

    If they are unmanaged switches then make sure that your servers are configured with auto-neg enabled on their NIC's as an unmanaged switch will have auto-neg enabled on every port, causing them to fall back to 100Mb half duplex when a NIC with Auto-neg disabled is connected.

    This kind of thing would not really be noticeable at traffic volumes below 5Mbps, but once you start going beyond that speed the duplex mismatch will cause severe throughput problems. (So if the traffic levels are increasing naturally and have been fairly low until recently its possible that the mismatch has been there for a while, just not noticed).


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