Check Packet Filtering
Any mistakes in packet filtering at the stack, router, proxy server, Routing and Remote Access service, or IPSec level can make address resolution or connectivity fail. To determine if packet filtering is the source of a network problem, you must disable the TCP/IP packet filtering.
To disable TCP/IP packet filtering
Click Control Panel, and then double-click the Network and Dial-up Connections icon.
Right-click the Local Area Connection , and then click Properties .
Select Internet Protocol (TCP/IP) , and then click the Properties tab.
Click Advanced , and then click Options .
Click TCP/IP Filtering in the Optional Settings window, and then click the Properties tab.
Clear the Enable TCP/IP Filtering (All Adapters) check box, and then click OK .
Try pinging an address using its DNS name, its NetBIOS name, or its IP address. If the attempt succeeds, the packet filtering options might be misconfigured or might be too restrictive. For instance, the filtering might permit the computer to act as a web server, but might in the process disable tools like Ping or remote administration. Restore a wider range of permissible filtering options by changing the permitted TCP, UDP, and IP port values.
If the attempt still fails, another form of packet filtering might still be interfering with your networking. For more information about Routing and Remote Access filtering functions, see "Unicast IP Routing" in the Microsoft ® Windows ® 2000 Server Resource Kit Internetworking Guide . For more information about IPSec packet filtering, see "Internet Protocol Security" in this book.