Enabling Split Horizon with Poison Reverse Causes Incorrect RIP Updates

ID: Q195640

The information in this article applies to:

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 fix. For information on obtaining the latest service pack, please go to:

For information on obtaining the individual fix, 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/support/supportnet/default.asp

NOTE: If this product was already installed on your computer when you purchased it from the Original Equipment Manufacturer (OEM) and you need this fix, please call the Pay Per Incident number listed on the above Web site. If you contact Microsoft to obtain this fix, and if it is determined that you only require the fix you requested, no fee will be charged. However, if you request additional technical support, and if your no-charge technical support period has expired, or if you are not eligible for standard no-charge technical support, you may be charged a non-refundable fee.

For more information about eligibility for no-charge technical support, see the following article in the Microsoft Knowledge Base:
Q154871 Determining If You Are Eligible for No-Charge Technical Support


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".

Additional query words: 4.00 rras multinet 


Keywords          : kbbug4.00 kbfix4.00 nt4sp5fix 
Version           : WinNT:4.0
Platform          : winnt 
Issue type        : kbbug

Last Reviewed: May 5, 1999