Chapter 15 Routing Protocols
ISG50 User’s Guide
307
Virtual Links
In some OSPF AS, it is not possible for an area to be directly connected to the backbone. In this
case, you can create a virtual link through an intermediate area to logically connect the area to the
backbone. This is illustrated in the following example.
Figure 203 OSPF: Virtual Link
In this example, area 100 does not have a direct connection to the backbone. As a result, you
should set up a virtual link on both ABR in area 10. The virtual link becomes the connection
between area 100 and the backbone.
You cannot create a virtual link to a router in a different area.
OSPF Configuration
Follow these steps when you configure OSPF on the ISG50.
1 Enable OSPF.
2 Set up the OSPF areas.
3 Configure the appropriate interfaces. See Section 12.3.1 on page 238.
4 Set up virtual links, as needed.
15.3.1 Configuring the OSPF Screen
Use the first OSPF screen to specify the OSPF router the ISG50 uses in the OSPF AS and maintain
the policies for redistribution. In addition, it provides a summary of OSPF areas, allows you to
remove them, and opens the OSPF Add/Edit screen to add or edit them.