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Q128647: Troubleshooting TCP/IP LAN and RAS Routing Issues

Article: Q128647
Product(s): Microsoft Windows NT
Version(s): winnt:3.5,3.51,4.0
Operating System(s): 
Keyword(s): kbnetwork
Last Modified: 08-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Workstation versions 3.5, 3.51, 4.0 
- Microsoft Windows NT Server versions 3.5, 3.51, 4.0 
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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

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Keywords          : kbnetwork 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351search kbWinNT350search kbWinNT400search kbWinNTW350 kbWinNTW350search kbWinNTW351search kbWinNTW351 kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS350 kbWinNTS351search kbWinNTS350search
Version           : winnt:3.5,3.51,4.0

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