KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q240059: Split Horizon with Poison Reverse Causes Incorrect RIP Updates

Article: Q240059
Product(s): Microsoft Windows NT
Version(s): winnt:4.0 SP5
Operating System(s): 
Keyword(s): kbWinNT4sp6fix
Last Modified: 20-MAY-2002

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Windows NT Server version 4.0, Terminal Server Edition 
- Microsoft Windows NT Server version 4.0 SP5 
-------------------------------------------------------------------------------

SYMPTOMS
========

When you configure Routing Information Protocol (RIP) with multiple adapters and
with all the default settings (including the Split Horizon with Poison Reverse
advanced settings), the RIP updates that are sent out have the correct metrics
for both of the RIP routes. However, RIP also advertises the routes that it
learns on the same subnet with a metric of 16 (poison reverse). On the Routing
and Remote Access Services (RRAS) computer that receives the RIP updates (with
the poison reverse update), the route should not be processed because RIP
already has a better route for that subnet (subnet A). It should also
distinguish the fact that this update is from a computer that is not the
destination router for that route to subnet A. However, RRAS processes that
route and therefore discards out a good route in favor of an unreachable route
(metric = 16). Any computer on its own remote subnet cannot reach this subnet
(subnet A), which now has a metric of 16.

RESOLUTION
==========

Windows NT Server or Workstation 4.0
------------------------------------

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or the
individual software update. For information on obtaining the latest service
pack, please go to:

- http://www.microsoft.com/Windows/ServicePacks/

-or-

- Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack

For information on obtaining the individual software update, contact Microsoft
Product Support Services. For a complete list of Microsoft Product Support
Services phone numbers and information on support costs, please go to the
following address on the World Wide Web:

  http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS


Windows NT Server 4.0, Terminal Server Edition
----------------------------------------------

To resolve this problem, obtain the latest service pack for Windows NT Server
4.0, Terminal Server Edition. For additional information, please see the
following article in the Microsoft Knowledge Base:

  Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack


STATUS
======

Microsoft has confirmed this to be a problem in Windows NT 4.0 and Windows NT
Server 4.0, Terminal Server Edition.

This problem was first corrected in Windows NT Server 4.0 Service Pack 6 and
Windows NT Server 4.0, Terminal Server Edition Service Pack 6.

MORE INFORMATION
================

The Split Horizon with Poison Reverse setting improves RIP convergence over a
simple split horizon by advertising all network IDs, but those network IDs
learned in a given direction are advertised with a metric of 16, indicating that
the network is unavailable. The Poison Reverse setting has no benefit beyond the
split horizon setting in a single-path internetwork. However, in a multiple-path
internetwork, the Split Horizon with Poison Reverse setting greatly reduces
counts to infinity and routing loops.

This behavior is described in Request for Comments (RFC) 1058, "Routing
Information Protocol."


Additional query words: 4.00

======================================================================
Keywords          : kbWinNT4sp6fix 
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTS400sp5 kbWinNTS400search kbNTTermServ400 kbNTTermServSearch
Version           : winnt:4.0 SP5
Hardware          : ALPHA x86
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.