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shortcuts (Protocols IS-IS)

 

Syntax

Hierarchy Level

Release Information

Statement introduced before Junos OS Release 7.4.

The family statement and support for IPv6 routes for IS-IS traffic engineering shortcuts introduced in Junos OS Release 9.3.

Description

Configure IS-IS to use MPLS label-switched paths (LSPs) as next hops if possible when installing routing information into the inet.3 or inet6.3 routing table. Internal gateway protocol (IGP) shortcuts allow the IGP to install prefixes in inet.3 or inet6.3.

It is only necessary to enable IGP shortcuts on the ingress router because that is the router performing the shortest-path-first (SPF) calculations.

It is important to understand how IGP shortcuts affect the protocol and routing table relationship. The IGP performs SPF calculations to subnets downstream of LSP egress points, but the results of these calculations are entered into the inet.3 table only. At the same time, the IGP performs its traditional SPF calculations and enters the results of these calculations into the inet.0 table. The result is that although the IGP is making entries into the inet.3 table, BGP is still the only protocol with visibility into that table for the purposes of route resolution. Therefore, forwarding to AS-internal destinations still uses the inet.0 IGP routes, and the LSPs are only used for BGP next-hop resolution. If you want the LSPs to be used for IGP next-hop resolution, you must configure traffic-engineering bgp-igp.

The remaining statement is explained separately. See CLI Explorer.

Required Privilege Level

routing—To view this statement in the configuration.

routing-control—To add this statement to the configuration.