Enabling Split Horizon with Poison Reverse Causes Incorrect RIP Updates (195640)
The information in this article applies to:
- Microsoft Windows NT Server 4.0
- Microsoft Routing and Remote Access Service Update for Windows NT Server 4.0
This article was previously published under Q195640 SYMPTOMS
When RIP is set with all the default settings, including the Advanced
settings of Split Horizon with Poison Reverse, the RIP update will occur
for both bound IP addresses but with an incorrect hop count (or metric) of
16. Because it advertises the metrics as 16, no other routers will know
that this computer is the router between those two subnets and, thus, the
two subnets will be unable to communicate with each other.
This problem occurs on a computer that is configured to use RIP and that
has a single network adapter configured for multiple IP addresses on
different subnets.
CAUSE
RRAS assigns an incorrect metric in outbound RIP requests when two IP
addresses are bound to the same network card.
RESOLUTION
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:
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:
STATUS
Microsoft has confirmed this to be a problem in Windows NT version 4.0. This problem was first corrected in Windows NT version 4.0 Service Pack 5.MORE INFORMATION
Split Horizon with Poison Reverse:
Split horizon with poison reverse improves RIP convergence over simple
split horizon by advertising all network IDs, but those network IDs learned
in a given directions are advertised with a metric of 16, indicating that
the network is unavailable. Poison reverse has no benefit beyond split
horizon in a single path internetwork. However, in a multipath
internetwork, split horizon with poison reverse greatly reduces count to
infinity and routing loops.
This behavior is described in RFC 1058, "Routing Information Protocol".
| Modification Type: | Minor | Last Reviewed: | 9/23/2005 |
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| Keywords: | kbHotfixServer kbQFE kbbug kbfix kbQFE KB195640 |
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