http://bj.ok2u.com.my/blog2/gallery/...p?g2_itemId=60


SCENARIO:

Above is the problem network diagram from my friend CC. They are running this network for 1 year plus without problem, the problem only appear recently. As you can see from the image attach above, they have 3 dynamic IP ADSL and 1 SDSL, and they are connected to a VPN using the SDSL to form a large LAN game network. The main switch "D-Link 24 port" is brand new because when they first discover this problem they tot is main switch problem and replace it from Linksys 16port to the current one.


PROBLEM:
The whole network cannot access the all 4 router by time to time.. when the problem come, all four router have no reply by PING..

To diagnose the problem I've tried to unplug the cable from switch 1 to switch 4 on the D-link switch, the problem goes when I unplug the switch 3 cable ...so i tot the problem come from switch 3.. so i replace switch3 to another switch (tempswitch3) and monitor the network using PING again. After a while, the problem come back, but removing the cable to tempswitch3 this time DOESN"T WORK! ... so I tried to remove cables to others switch and when I remove cable to switch2, the problem have GONE!! and the problem repeat and repeat later on different switch.

So i thought it is virus problem because I experience something similar before (the Arp spoofing which i can detect using winarpattacker.exe). But this time is different, the winarpattacker doesn't detect any IP spoofing/flooding.. So do anyone here experience the similar situation before? Can someone point out the possibilities?

Help please.

Thanks.