Routing IP Packets to Network Adapter Rather than RAS

Last reviewed: September 18, 1997
Article ID: Q143168

The information in this article applies to:

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

SUMMARY

Pages 419 to 421 of the Windows NT Networking Guide in the Windows NT 3.5 Resource Kit and the following article in the Microsoft Knowledge Base explain how you can configure the Windows NT Remote Access Service (RAS) using the TCP/IP protocol to perform as a simple router:

   ARTICLE-ID: Q121877
   TITLE     : Using RAS for Routing of IP Packets

The routing is between the RAS connection and the network adapter in your local area network (LAN). However, if the following conditions are met, all network packets are sent over the RAS connection:

   - Your RAS connection and network adapter are using two different
     subnetwork addresses in the same network.

   - You select Use Default Gateway On Remote Network check box for
     Windows NT RAS.

This article explains how you can direct network packets to the network adapter.

MORE INFORMATION

To send packets to your network adapter, do the following in the registry:

WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

Start Registry Editor (REGEDT32.EXE) and locate the following Registry subkey in the HKEY_LOCAL_MACHINE subtree:
\SYSTEM\CurrentControlSet\Services\RasMan\PPP\IPCP
From the Edit menu, select Add Value.

Enter the following:

      Value Name: PriorityBasedOnSubNetwork
      Data Type:  REG_DWORD
      String:     1 (Enable)

Click OK and quit the Registry Editor.
At a command prompt type:
```
      net stop remoteaccess
```
At a command prompt type:
```
      net start remoteaccess
```

EXAMPLE

If your network adapter address is 10.1.1.1 and your RAS connection uses the address 10.2.1.1 and your subnet mask is 255.255.0.0, the network packets is forwarded to 10.2.1.1. The addresses 10.1.0.0 and 10.2.0.0 are two different subnetworks in the Class A 10.0.0.0 network. If you do not enable the PriorityBasedOnSubNetwork parameter, the following entries appear in your route table (assuming that you have selected the Use Default Gateway on Remote Network check box in RAS):

Network Address      Netmask     Gateway Address   Interface  Metric
---------------      -------     ---------------   ---------  ------
    0.0.0.0          0.0.0.0        10.2.1.1        10.2.1.1     1
   10.0.0.0        255.0.0.0        10.2.1.1        10.2.1.1     1
   10.1.0.0       255.255.0.0       10.1.1.1        10.1.1.1     2 *
   10.1.0.0       255.255.0.0       10.2.1.1        10.2.1.1     1 *
   10.1.1.1      255.255.255.255   127.0.0.1       127.0.0.1     1
   10.2.1.1      255.255.255.255   127.0.0.1       127.0.0.1     1
10.255.255.255   255.255.255.255    10.1.1.1        10.1.1.1     1
  127.0.0.0        255.0.0.0       127.0.0.1       127.0.0.1     1
  224.0.0.0        224.0.0.0        10.2.1.1        10.2.1.1     1
  224.0.0.0        224.0.0.0        10.1.1.1        10.1.1.1     1
255.255.255.255  255.255.255.255    10.1.1.1        10.1.1.1     1

Due to the two entries above (noted with *), all packets are sent over the RAS connection with the address 10.2.1.1. If you enable PriorityBasedOnSubNetwork, the following entry is removed from the route table:

Network Address      Netmask      Gateway Address  Interface  Metric
---------------    -----------    ---------------  ---------  ------
    10.1.0.0       255.255.0.0      10.2.1.1        10.2.1.1     1

If you have additional subnetworks in the 10.0.0.0 network and you want the packets to reach the correct subnetwork, add static routes to the route table. You can also use the Multi-Protocol Router (MPR) software available in the Windows NT 3.51 Service Pack 2. For more information on adding static routes to the route table in Windows NT, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q140859
   TITLE     : TCP/IP Routing Basics for Windows NT

Additional query words: prodnt TCPIP lose packets lose connectivity
Keywords : NTSrvWkst nttcp kbnetwork
Version : 3.5 3.51 4.0
Platform : winnt

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Last reviewed: September 18, 1997
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