RRAS IPX VPNs Generate Event ID 20124

When your client computers try to access resources across a Routing and Remote Access (RRAS) Point-to-Point Tunneling Protocol (PPTP) tunnel routing IPX, your RRAS server will log the following error:

RRAS will also stop forwarding IPX and SAP.

The IPX stack sees that a packet from the clients LAN is trying to go over the WAN adapter and it then uses this network number of the client as the autonet value for the adapter. The network number is incorrect and will cause routing to stop.

If you receive event ID 20124, you will need to disable the ability of RRAS to use unnumbered WAN connections.

You can make this change by editing the following registry entry.

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it. If you are running Windows NT, you should also update your Emergency Repair Disk (ERD).

1. Run Registry Editor (Regedt32.exe).
2. Go to the following key in the registry:
   

         HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RemoteAccess
         \Parameters\Ipx
   						

   
   NOTE: The above registry key is one path; it has been wrapped for readability.
3. On the Edit menu, click Add Value and use the following entry (if the entry already exists, just double-click it to edit the value):
   

         Value Name:    EnableUnnumberedWanLinks
         Data Type:     REG_DWORD
         Value range:   0 - 0xFFFFFFFF
         Default value: 1
   						

   
   By default, this value is 1. Change this value to 0.

Consider the following environment:

Both RRAS servers (LRRAS and RRRAS) have two network cards.

On LRRAS, one network card is configured with IPX only (net ID dddd) and the other network card is configured with IPX (net ID cccc) and an IP address on the 10.0.0.0/8 network. The internal network ID is configured to be ddcc. The X in the diagram represents IPX outbound filters (drop all) and IP outbound filters (allow only PPTP).

On RRRAS, one network card is configured with IPX only (net ID bbbb) and the other network card is configured with IPX (net ID cccc) and an IP address on the 10.0.0.0/8 network. The internal network id is configured to be ccbb. The X in the diagram represents IPX outbound filters (drop all) and IP outbound filters (allow only PPTP).

The filters assure that IPX traffic will only flow over the PPTP tunnel created between the two RRAS servers.

Lclient and Rclient only have IPX bound to their NICs and have internal network IDs defined as eeee and aaaa respectively.

On the RRAS servers, both RIP and SAP have been configured on the LAN and WAN interfaces.

As soon as client eeee tries to view client aaaa, the VPN adapter on LRRAS changes the net ID of the WAN interface from all zeroes (the default) to eeee, which RRRAS cannot handle. It logs error 20124 and stops routing IPX packets.

After the above error is logged, IPX routing is stopped and both RIP and SAP timeout over the PPTP connection.