Domain Controllers Unable to Communicate Over IPX Token-Ring WAN

• Microsoft Windows NT Server version 3.51
• Microsoft Windows NT Server version 4.0

SUMMARY

This article helps you configure routed IPX running over Token Ring to properly support communication between Windows NT Server 3.51 domain controllers. This article is specific to ACC Nile Routers with no filtering, running IPX over Token Ring in a non-NetWare environment, although it is likely to be applicable to other routers. It is assumed that the Windows NT 3.51 servers are running only the NWLINK protocol.

The problem symptoms are that a Windows NT 3.51 Primary Domain Controller (PDC) cannot communicate over the WAN with one of its Backup Domain Controllers (BDCs) - drives cannot be mapped, browse lists are not correct and the domain cannot be synchronized.

MORE INFORMATION

• Make sure the routers are NOT filtering any type 20 (Hex 14) WAN broadcast IPX packets on the WAN link.
• Make sure NETBIOS is enabled on the routers.
• - Make sure that the SAP Agent service is running on both the PDC and

• The two DCs may be trying to communicate at a bigger frame size (4096 bytes). The size of these packets going over a WAN link may be slow enough for their connection to time-out. Use regedt32 and add a REG_DWORD value of 576 to RouterMTU. It should be added to:

  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NwlnkNb\Parameter

  This limits the size of the NETBIOS over NWLink IPX packets to 576 bytes. You can fine tune this setting to achieve optimal throughput. The ACC Nile routers have a default value for their maximum transmission unit of 576 bytes. This can be modified using the "Set IPX network MTU" command and can range from 576 bytes to 4491 bytes on Token-Ring networks.

• Make sure the IPX net numbers and frame types for the DCs match the network segments on which they are located, especially if you have initially configured and tested them on the same segment before moving the BDC across the WAN link.