Overview

In JUNOS Release 5.3 and earlier, interinstance route sharing often required configuration of routing table groups by means of the rib-group statement. Although these configurations performed well, the routing table group technique had several limitations:

• Lack of intuitiveness—A routing table group is an unfamiliar configuration construct for many users.
• Complex configuration requirements—Routing table groups specify a primary import routing table that must match the routing table of the VRF instance on which they are applied. Thus, a different routing table group is defined for each of the instances that participate in interinstance route export.
• Redundancy—The information imported and exported by the routing table groups is already present in the router or can be deduced from most configurations (for example, overlapping VPNs).
• Per-protocol configuration—Routing table groups must be applied to every protocol containing routes designated for export.

There are two typical situations in which interinstance export is used:

• Overlapping VPNs—VPN configurations where more than one VRF instance lists the same community route target in a vrf-import policy. In this case, the use of routing table groups is particularly tricky. Incoming routes from other provider edge (PE) routers are automatically imported according to the community route targets, but local VRFs require additional configuration.
• Nonforwarding instances—Multilevel interior gateway protocols (IGPs) that have multiple routing instances and perform route sharing through interinstance route export. The IGP export policy contains the specific instances that are permitted to advertise routes.

These two scenarios differ in the way that policy clauses are specified (route targets in the VRF case; instances in the IGP routing instance case), but are similar in that import and export routes can be deduced by examining the policy configuration. In this guide, you can learn about new hierarchy statements that simplify interinstance route sharing, such as auto-export, instance-import, and instance-export.

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