This article was previously published under Q223756
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IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:
256986 Description of the Microsoft Windows Registry
You require Internet Control Message Protocol (ICMP) Internet Router Discovery Protocol (IRDP) support on Microsoft Windows NT
IRDP (router discovery) support has been added to Windows NT 4.0. IRDP support has also added to Windows 95 and 98 (see the "More Information" section of this article).
The following text is an excerpt from Request for Comments (RFC) 1256:
The ICMP router discovery messages are called "Router Advertisements" and "Router Solicitations. " Each router periodically multicasts a Router Advertisement from each of its multicast interfaces, announcing the IP address(es) of that interface. Hosts discover the addresses of their neighboring routers simply by listening for advertisements.
This is one way of testing for dead gateways. This solution requires that routers be configured to send IRDP router advertisement packets.
Windows NT 4.0 now supports performing "router discovery" as specified in RFC 1256.
Router discovery provides an improved method of configuring and detecting default gateways. When using DHCP or manual default gateway configuration, there is no way to adjust to network changes. Using router discovery, clients dynamically discover routers and can switch to backup routers if a network failure or administrative change is needed. Router discovery is made up of two types of packets: Router Solicitations sent by hosts, and Router Advertisements sent by routers. Windows NT 4.0 supports router discovery as a host only.
This feature is disabled by default.
WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
Router discovery is configured from the following registry keys:
Value Name: PerformRouterDiscovery Value Type: REG_DWORD - Number Valid Range: 0,1 Default: 0 Description: This parameter controls whether Windows NT will attempt to perform router discovery per RFC 1256 on a per-interface basis. This parameter defaults to 0 or FALSE.
Value Name:SolicitationAddressBcast Value Type: REG_DWORD - Number Valid Range: 0,1 Default: 0 Description: This parameter can be used to configure Windows NT to send router discovery messages as limited broadcasts (255.255.255.255) instead of multicasts, as described in RFC 1256. By default, router discovery solicitations are sent to the all routers multicast group (126.96.36.199). By default, IRDP client listens to both multicast and broadcast router advertisements.
Quit Registry Editor.
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 that this is a problem in Windows NT 4.0. This problem was first corrected in Windows NT version 4.0 Service Pack 5.
When a host that supports router discovery initializes, it joins the "all-systems" IP multicast group (188.8.131.52), and then listens for the router advertisements sent to that group.
Hosts send ICMP Router Solicitation messages to the all routers IP multicast address (184.108.40.206). The router will respond by sending a router advertisement. This ensures the client receives a default gateway immediately without waiting for a periodic router advertisement. Windows NT sends a maximum of 3 solicitations at intervals of approximately 600 milliseconds.
NOTE: If multiple default gateways (0.0.0.0 routes) have a metric of 1, random routing behavior can occur. For additional information, see the following article or articles in theMicrosoft Knowledge Base:
159168 Multiple Default Gateways Can Cause Connectivity Problems
For IRDP support, Windows 95 requires Windows Socket update 2; Windows 98 natively supports IRDP.For additional information, see the following article or articles in theMicrosoft Knowledge Base:
183902 Dead Gateway Detection Is Not Triggered During Logon
For additional information about the IPRIP Listener Tool for Windows 98, click the article number below to view the article in the Microsoft Knowledge Base:
194464 Description of the Microsoft IPRIP Listener Tool for Windows 98