Situation
The client reported that their access to the Internet very slow while the LAN speed seemed OK.
Troubleshooting
1. When testing by ping each other in the LAN, the time<1ms.
2. Ping chicagotech.net from the inside, the time>3000ms.
3. Ping the router from outside, the time>3000ms.
4. Unplugged the inside cable connecting the router, ping from outside receive time<10ms.
It seemed to us there is a networking device sent a lot packets to the Internet. Running anti-virus on all computer and found one Windows 2000 server as web and imail server had trojan virus. The internet access went back to normal after clean the trojan virus.