How to Use OSPF with RRAS Demand-Dial and VPN Connections

ID: Q200834

The information in this article applies to:

Microsoft Routing & Remote Access Service Update for Windows NT Server version 4.0

SUMMARY

This article describes how to implement Open Shortest Path First (OSPF) over Routing and Remote Access Services (RRAS) Dial-on-Demand (DOD) connections. The implementation of this protocol is the same for both direct-dial modem connections and virtual private network (VPN) connections over the Internet.

MORE INFORMATION

OSPF over a direct-dial connection used for LAN-to-LAN routing:


   Lclient           L-RRAS === Modem() === R-RRAS           Rclient
       |      IP      |                        |      IP      |
        --------------                          --------------

OSPF over a VPN connection used for LAN-to-LAN routing:


   Lclient           L-RRAS ===== VPN ===== R-RRAS           Rclient
       |      IP      |  |      Internet     |  |      IP      |
        --------------    -------------------    --------------

For the purposes of this article, a DOD connection refers to either a Dial-on-Demand connection between two RRAS servers using modems or a VPN tunnel.

When you are configuring OSPF for LAN-to-LAN routing, as in the two scenarios above, verify the following items:

Make sure that the DOD connections dial and connect successfully. This is true for both modem connections and VPN connections. You can put temporary static routes on the RRAS servers to test the routing capabilities. OSPF does not work if the DOD connections cannot connect.

In the RRAS Administration tool, under IP Routing, right-click Summary, and then click Add Routing Protocol. Click OSPF by Bay Networks, and then click OK.

Configuring the OSPF Protocol

During the installation of the OSPF protocol, you are prompted to select options for event logging on the General tab and for security options on the Security tab. Leave these options at their default settings for now.

After OSPF is installed, a new OSPF by Bay Networks icon appears under IP Routing. Add the adapters that OSPF will use in this section. Add both the DOD adapters and the LAN-side adapters. For VPN, it is not necessary to add the network adapter that connects to the Internet, unless there are other compelling reasons to do so.

After determining the necessary adapters, right-click OSPF by Bay Networks, and then click Add Adapter. Click the DOD adapter being used between your two RRAS servers. Do this on both RRAS servers.

After you add an adapter, there are configuration options on the General, Neighbors, and Advanced tabs. Note that the Enable OSPF on this adapter check box is not selected by default. Click to select this check this box to enable OSPF on the adapter being added.

Note that OSPF is a complex protocol and requires knowledge of how to use and configure it. This article points out a few caveats to using OSPF over DOD connections, but does not attempt to explain the OSPF protocol itself.

In the Configuration dialog box, you may need to change the Area ID, Cost, and Password settings. There is also a Type section at the bottom of the General tab that has three choices.

LAN network adapters (such as an Ethernet adapter) use the Broadcast type. This is a slight misnomer because OSPF primarily uses multicast traffic to communicate.

If you are configuring a frame relay network that does not support broadcasts, click NBMA (which stands for Non-Broadcast-Multiple-Access network). If you are configuring NBMA, you must configure specific IP addresses for OSPF neighbors on the Neighbors tab.

The Point-to-Point type is used for DOD connections because these connections are point-to-point by nature.

You do not need to change anything on the Neighbors tab unless you are using OSPF on an NBMA network.

Broadcast types are configured with a default cost of 2, whereas Point-to-Point types are configured with a default cost of 4.

The Advanced tab contains options for configuring various OSPF parameters for the autonomous system of which these RRAS servers and LANs are a part.
For more information about OSPF configuration, please see the RRAS Administration Guide in the C:\Program Files\Routing\Docs folder that is installed with RRAS.
You can make changes or alterations to the behavior of OSPF after the initial configuration of the adapters.

At this point, even though OSPF is installed and the adapters are configured to bind to OSPF, the DOD connections do not dial and are not forced to dial by OSPF. For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

Q235492 RIP and OSPF Do Not Start Dial-on-Demand Connections

To force a DOD connection to dial, add a default gateway static route pointing to the DOD connection, or specify a network route pointing to the DOD connection. Do this on both RRAS servers for routing purposes. In this scenario, the administrator must add the static routes manually; OSPF learned routes are placed in the routing table after the DOD connection is connected. If you add static routes in this configuration, the following configuration option is available:

OSPF learned routes can be configured to have a lower or preferred metric over static routes. You can configure this in the RRAS Administration tool on the IP Routing tab. Right-click Summary, and then click Configure IP parameters. Click the Preference Levels tab. You can set preference levels for routes based on their type. You can modify OSPF by Bay Networks to have a preference level of 1 rather then the default level of 3. This causes OSPF learned routes to have preference over static routes.

Additional query words:

Keywords : kbenv kbnetwork
Version : winnt:4.0
Platform : winnt
Issue type : kbinfo