Both Adapters Can be Reached in Multihomed Windows NT Computer

ID: Q139334

The information in this article applies to:

SUMMARY

On your network with a server running Windows NT with two network interface cards (NICs) installed (also referred to as a multihomed computer), you are able to ping both adapters on the multihomed server from each subnet even though routing is not enabled on the server.


MORE INFORMATION

A Windows NT server only maintains one routing table for both NICs. When a network client from either subnet attempts to access the first or second NIC, Windows NT checks in the routing table for the NIC IP address the client is trying to access. Because the IP address exists in the Windows NT server routing table as a local address, Windows NT responds to the network client. The default gateway address of the client must be the address of the adapter in the non-routing, multihomed server that is on the same subnet.

However, Windows NT does not route packets between clients of the subnets on the two NICs unless routing is enabled.

Steps to Reproduce Problem

  1. Setup a multihomed Windows NT computer with TCP/IP installed.


  2. Verify that both NICs are addressed to exist on different subnets, Subnet_A and Subnet_B.


  3. Verify that the Enable IP Routing option is clear (unchecked) on the Windows NT server. To find this option:


    1. Run Control Panel and choose Networks.


    2. From the list of Installed Network Software, select TCP/IP Protocol.


    3. Choose Configure and then Advanced.


  4. Setup a client on Subnet_A connected to the Windows NT server and configure the client with a Subnet_A IP address.


  5. Set the client Default Gateway address to the IP address of the Subnet_A NIC in the Windows NT server.


  6. From the client ping the Windows NT server Subnet_A and Subnet_B NIC addresses.



NOTE: You can ping the Windows NT server Subnet_A NIC IP address as expected, however, you can also ping the Subnet_B NIC IP address even though IP routing is not enabled on the Windows NT server.

Additional query words: prodnt mpr 


Keywords          : kbnetwork nttcp NTSrvWkst 
Version           : 3.5 3.51 4.0
Platform          : winnt 
Issue type        :

Last Reviewed: January 26, 1999