ICMP Redirect Routes Override OSPF Routes

ID: Q243427

The information in this article applies to:

Microsoft Windows NT Server versions 4.0 SP4, 4.0 SP5
Microsoft Windows 2000 Advanced Server
Microsoft Windows 2000 Server

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.

SYMPTOMS

When Routing and Remote Access Services (RRAS) is configured as an autonomous system boundary router (ASBR), it does not correctly import connected interface subnet routes. Instead, it injects host routes into the Open Shortest Path First (OSPF) routes. Because the OSPF router cannot be used as an ASBR router, importing connected interface subnet routes into OSPF results in confusing routing tables with strange routing paths.

CAUSE

Internet Control Message Protocol (ICMP) redirects cause the stack to plumb host routes. These routes override the OSPF-generated routes. This, by itself, is the expected behavior. The problem, however, is that for a period of time (the period of the ICMP redirect-plumbed routes' timeout, which is ten minutes) there is a black hole for the network concerned.

RESOLUTION

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys and Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it. If you are running Windows NT, you should also update your Emergency Repair Disk (ERD).

To resolve this issue, turn off the routes being plumbed by ICMP redirects. In Windows 2000, you can do this by adjusting a registry value as follows:

Start Registry Editor (Regedt32.exe).

Locate the following key in the registry:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

Change the data value of the EnableICMPRedirect value to 0 (by default, it is 1).

Quit Registry Editor.

STATUS

Microsoft has confirmed this to be a problem in Windows 2000.

Additional query words:

Keywords : kbenv kbnetwork
Version : WINDOWS:2000; winnt:4.0 SP4,4.0 SP5
Platform : WINDOWS winnt
Issue type : kbprb