No Network Connectivity on TCP/IP-Based Network

Article translations Article translations
Article ID: 185753 - View products that this article applies to.
This article was previously published under Q185753
If this article does not describe your hardware-related issue, please see the following Microsoft Web site to view more articles about hardware:
Expand all | Collapse all


You may not be able to view or connect to any shared resources on a network that uses the Transport Control Protocol/Internet Protocol (TCP/IP), even though your network adapter and network server settings have been verified to work correctly.


This problem can occur if you change the Internet Protocol (IP) address for your computer to any of the following invalid IP addresses in the TCP/IP Properties dialog box:
  • 127.<x>.<y>.<z>
To specify any of these addresses, you must click Specify An IP Address on the IP Address tab in the TCP/IP Properties dialog box, type the invalid TCP/IP address, click OK, click OK when you receive the following message, and then click Cancel:
The specified IP address is not valid. Please check that the value you typed is correct. If you believe the value is correct but you still receive this message, check with your network administrator.


To work around this problem, change the IP address to a valid IP address. To do so, follow these steps:
  1. Click Start, point to Settings, click Control Panel, and then double- click Network.
  2. On the Configuration tab, double-click either TCP/IP or "TCP/IP-><network adapter>," where <network adapter> is the name of your network adapter.
  3. On the IP Address tab, type a valid IP address in the IP Address box, and then click OK. If you do not know a valid IP address for your computer, contact your network administrator.
  4. Click OK, and then click OK.


Microsoft has confirmed this to be a problem in Microsoft Windows 95, Windows 98 and Windows Me.


Networks that use TCP/IP set a unique IP address for each computer to determine its identity. The IP address is reserved for testing the TCP/IP stack with the PING command. The following table lists IP addresses that are not valid for a computer, where <x.y.z> is a range of numbers from 0 to 254.

   Invalid IP address   Valid (reserved) usage
   -----------------------------------------------------            Loopback/LocalHost address            Class A subnet mask          Class B subnet mask        Class C subnet mask
   225.<x.y.z> -        Class D address (multicast only)
240.<x.y.z> - Class E address (reserved)
254.<x.y.z> Broadcast address

If you use any of the addresses listed above as the IP address for a computer, no other computer can successfully communicate with it.

A subnet mask is an address for a subnetwork used to expand the range of possible IP addresses on the network. A subnet mask acts to identify an IP address on different subnetworks. TCP/IP uses the binary format to resolve an IP address and subnet mask.

Both the IP address and the subnet mask use binary format for each octet. An IP address consists of four octets. The portion of the octet in binary format that is not used by the subnet mask becomes the portion of the IP address that differentiates it from other IP addresses on the same subnetwork. The assigned IP address and the subnet mask are combined in binary format to create the resolved IP address in a TCP/IP network. If the resolved IP address in binary format is all zeros or ones (for example, 11111111, or decimal 255), it is an invalid IP address.

The following table lists sample IP addresses and subnet masks for an IP address on a Class C subnetwork. These addresses assume that the first three octets of each IP address and subnet mask are valid.
   IP address     Subnet mask      Resolved IP address   Result
   00000001 (1)   11111100 (252)   11111101 (253)        valid
   00000011 (3)   11111100 (252)   11111111 (255)        invalid

For information about troubleshooting TCP/IP, please see the following article in the Microsoft Knowledge Base:
ARTICLE-ID: 172218
TITLE : Microsoft TCP/IP Host Name Resolution Order


Article ID: 185753 - Last Review: January 23, 2007 - Revision: 2.1
  • Microsoft Windows Millennium Edition
  • Microsoft Windows 95
  • Microsoft Windows 98 Standard Edition
kbenv kbnetwork kbprb KB185753

Give Feedback


Contact us for more help

Contact us for more help
Connect with Answer Desk for expert help.
Get more support from