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Q235492: RIP and OSPF Do Not Start Dial On Demand Connections

Article: Q235492
Product(s): Microsoft Windows NT
Version(s): 2000,4.0
Operating System(s): 
Keyword(s): kbenv kbnetwork kbtool
Last Modified: 05-FEB-2002

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The information in this article applies to:

- Microsoft Windows NT Server version 4.0 
- Microsoft Routing and Remote Access Service Update for Windows NT Server version 4.0 
- Microsoft Windows 2000 Advanced Server 
- Microsoft Windows 2000 Datacenter Server 
- Microsoft Windows 2000 Server 
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SUMMARY
=======

Routing Information Protocol (RIP) and Open Shortest Path First (OSPF) are
protocols designed to detect unsuccessful network connections and report these
network problems to neighboring routers through time-out mechanisms. This means
that these protocols are designed to believe that network connections are
permanent unless they are actually down.

When you are using Dial On Demand (DOD) interfaces within RRAS, it is understood
that these connections are up only when needed, and are disconnected when no
traffic is being routed.

MORE INFORMATION
================

It is necessary to add static routes in the route table to trigger a DOD
interface to make a connection. This is the opposite of how RIP and OSPF
operate, because RIP and OSPF do not require static routes to operate. In fact,
RIP and OSPF are designed to prevent an administrator from having to add static
routes to a route table. RIP and OSPF simply listen for dynamic route updates
and add new routes to the route table as appropriate.

Therefore, RRAS dynamic routing protocols such as RIP and OSPF do not dial a DOD
connection when a normal networking path does not succeed. Neither RIP nor OSPF
in Windows NT 4.0 RRAS has the capability to force the dialing of a DOD
connection if another route does not work. When a route or network path does not
succeed, you must still have static routes available to force the dialing of a
DOD connection. To keep the static routes from interfering with normal RIP and
OSPF operation, simply add static routes with higher associated costs than the
normal network connection.

You can identify the priority order for routes learned by the RRAS server. In the
RRAS Administration tool, under IP Routing, right-click Summary, and then click
Properties. On the Preference Level tab, make sure that static routes are listed
as less preferred than RIP or OSPF. The lower the number, the higher the
preference. This way, when a network route does not work and times out, the RRAS
server sees the higher-metric static route and forces a dial-up connection to
the other network. Once the connection is up and authenticated, both RIP and
OSPF operate as if the DOD connection was a permanent LAN connection.

A drawback to this strategy is that when the original network route becomes
available again, the DOD connection may stay up indefinitely. Traffic is routed
across the original network interface as it is supposed to be, but the DOD
connection does not drop because of the idle time-out properties. This occurs
because RIP and OSPF believe that the DOD connection is permanent and continue
to send packets along these paths to keep themselves updated. This can prevent
idle time-out events from occurring and can result in the connections staying up
indefinitely.

Unless they are carefully configured, RIP and OSPF packets do not allow an idle
time-out mechanism to occur on these DOD connections. This can result in
additional expense if you are dialing long distance or using ISDN lines.

Additional query words:

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Keywords          : kbenv kbnetwork kbtool 
Technology        : kbWinNTsearch kbWinNT400search kbwin2000AdvServ kbwin2000AdvServSearch kbwin2000DataServ kbwin2000DataServSearch kbwin2000Serv kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbwin2000ServSearch kbwin2000Search kbAudDeveloper kbWinAdvServSearch kbWinDataServSearch kbRRASNTSearch kbRRASNT400
Version           : :2000,4.0
Issue type        : kbinfo

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