Microsoft KB Archive/128647

= Troubleshooting TCP/IP LAN and RAS Routing Issues =

Article ID: 128647

Article Last Modified on 11/1/2006

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APPLIES TO


 * Microsoft Windows NT Workstation 3.5
 * Microsoft Windows NT Workstation 3.51
 * Microsoft Windows NT Workstation 4.0 Developer Edition
 * Microsoft Windows NT Server 3.5
 * Microsoft Windows NT Server 3.51
 * Microsoft Windows NT Server 4.0 Standard Edition

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This article was previously published under Q128647



SUMMARY
You may not be able to ping or otherwise connect to computers across a router using the TCP/IP protocol while you are connected as a RAS client to a remote Windows NT 3.5 or 4.0 Remote Access Service (RAS) server.



CAUSE
This problem occurs if you have "Use default gateway on remote network" selected under TCP/IP settings in the RAS Phonebook. This feature adds a route to the route table. The new route allows IP addresses that are not resolved by other entries in the route table to be routed to the gateway on the RAS link. To use Internet utilities, such as a WEB browser or FTP, this feature must be enabled.



MORE INFORMATION
You can observe the change to the default route in the route tables by using the Route Print command at the Windows NT Command Prompt. For example, if you make a connection with RAS and issue the Route Print command, the first line of the IP routing table will look like the following (actual Gateway and Interface values will vary):

  Network Address   Netmask   Gateway Address  Interface         Metric 0.0.0.0          0.0.0.0   199.199.41.1     199.199.41.254      1

This first line is the natural default path to the local LAN gateway. If you connect with RAS to the remote Windows NT 3.5 RAS server, the first two lines of the Route Print command will appear as follows:

  Network Address   Netmask   Gateway Address  Interface         Metric 0.0.0.0          0.0.0.0   199.199.41.1     199.199.41.254      2   0.0.0.0           0.0.0.0   199.199.32.15    199.199.32.15       1

The metric value represents the number of hops a packet must take to its destination. Because the new route to the default Gateway is shorter (metric value 1), it becomes the preferred path. If you try to use the Route Delete command to erase the RAS default gateway, the second line is removed. RAS replaces the first line with the RAS default gateway path. As a result, it looks like the first line of the table is deleted instead of the second line. For example, when you try to delete the second line of the above table, the result is:

  Network Address   Netmask   Gateway Address  Interface         Metric 0.0.0.0          0.0.0.0   199.199.32.15    199.199.32.15       1



RESOLUTION
To use TCP/IP utilities, leave the "Use default gateway on remote network" selection turned on.

Use the Route Add command to add the route of the subnet you are attempting to use and tie that route to the local gateway. For example, if the computer you are connecting to has an IP address of 11.1.0.3, add following command to the route table:

  Route Add 11.0.0.0 Mask 255.0.0.0 199.199.41.1

This addition causes all frames bound for the 11.x.x.x subnet to be processed through the local LAN gateway on the local network.

The result is as follows:

  Network Address   Netmask   Gateway Address  Interface         Metric 0.0.0.0          0.0.0.0   199.199.41.1     199.199.41.254      2   0.0.0.0           0.0.0.0   199.199.32.15    199.199.32.15       1   11.0.0.0          255.0.0.0 199.199.41.1     199.199.41.254      1

Additional query words: tcpip dun

Keywords: kbnetwork KB128647

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