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Enabling Split Horizon with Poison Reverse Causes Incorrect RIP Updates

This article was previously published under Q195640
This article has been archived. It is offered "as is" and will no longer be updated.
When RIP is set with all the default settings, including the Advancedsettings of Split Horizon with Poison Reverse, the RIP update will occurfor both bound IP addresses but with an incorrect hop count (or metric) of16. Because it advertises the metrics as 16, no other routers will knowthat this computer is the router between those two subnets and, thus, thetwo subnets will be unable to communicate with each other.

This problem occurs on a computer that is configured to use RIP and thathas a single network adapter configured for multiple IP addresses ondifferent subnets.
RRAS assigns an incorrect metric in outbound RIP requests when two IPaddresses are bound to the same network card.
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:
  • 152734 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:
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.
Split Horizon with Poison Reverse:

Split horizon with poison reverse improves RIP convergence over simplesplit horizon by advertising all network IDs, but those network IDs learnedin a given directions are advertised with a metric of 16, indicating thatthe network is unavailable. Poison reverse has no benefit beyond splithorizon in a single path internetwork. However, in a multipathinternetwork, split horizon with poison reverse greatly reduces count toinfinity and routing loops.

This behavior is described in RFC 1058, "Routing Information Protocol".
4.00 rras multinet

Article ID: 195640 - Last Review: 12/05/2015 09:40:00 - Revision: 3.0

Microsoft Windows NT Server 4.0 Standard Edition

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