Configuring Nonforwarding Instances
In nonforwarding instances implemented in Junos OS Release 5.3 and earlier, you could configure interinstance export through use of import routing table groups. A secondary routing instance would import routes from the primary routing instance. Then, IGPs would advertise the routes received from the second instance table as shown in the example in Figure 1.
Figure 1: Nonforwarding Instance Concept
In Junos OS Release 5.4 and later, you can use the instance-import and instance-export policy keywords to perform nonforwarding, interinstance route sharing. The keywords are assigned at the [edit routing-instances instance-name routing-options] hierarchy level. These statements are similar to VRF import and VRF export policies used for VRF instances.
The “rt-export” module examines the from instance statements present in an instance import policy to construct the list of import tables for a particular exporting instance. The following example illustrates the configuration hierarchy for this feature:
To advertise instance blue routes through an instance red IGP such as OSPF, you would add an export policy to OSPF to advertise routes from the local table.
When an instance import policy is configured, the policy is allowed to modify route attributes other than next-hop.
