I've a strange problem on Cisco 857 act as ADSL router. Some clients couldn't open http://www.microsoft.com website and also couldn't online with MSN. The problem was gone when I replaced the Cisco with another router such as D-Link or Huawei. I didn't configure any firewall and IPS on the router. I already upgraded IOS to the latest version but the problem still occurred. How can I troubleshoot this issue?