Overview

Prior to JUNOS Release 5.4, the two mechanisms used to enable rapid MPLS LSP reroutes in Juniper Networks routers were Packet Forwarding Engine local repair and fast reroute. Packet Forwarding Engine local repair is an infrastructure-based solution and fast reroute provides a single backup LSP for every protected primary LSP. However, configuring backup LSPs on a one-to-one basis can become a scaling challenge for a growing MPLS network.

JUNOS Release 5.4 and later provide a scalable solution for LSP redundancy in an option called link protection. The link protection approach is explained in the IETF Internet draft Fast Reroute Extensions to RSVP-TE for LSP Tunnels. In general, it is a facility-based method designed to reroute traffic from multiple LSPs quickly. It also reduces the amount of configuration necessary to implement LSP protection.

You can configure link protection by itself, fast reroute by itself, or both simultaneously. Whenever one or both of these reroute options are enabled, Packet Forwarding Engine local repair is activated by default.

To enable any of Juniper Networks MPLS LSP reroute options, you must first install the LSP as a valid next hop in the main inet.0 routing table on the ingress PE router. You can accomplish this in one of several of ways:

• Enable the BGP learned routes to use the LSP.
• Set the bgp-igp or bgp-igp-both-ribs parameters at the [edit protocols mpls traffic engineering] hierarchy level.
• Configure install prefix active at the [edit protocols mpls lsp lsp-name] hierarchy level.
• Configure a static route with an indirect next hop that goes to the LSP end.
• Configure a static route with an LSP next hop.
• Configure IS-IS support for bidirectional LSPs.

To summarize, the MPLS LSP reroute options available in JUNOS are as follows:

• Packet Forwarding Engine local repair—This data plane method adds enhanced capabilities to the Packet Forwarding Engine subsystem and reduces the time needed for path switchover. With local repair, the Packet Forwarding Engine can correct a path failure before it receives recomputed paths from the Routing Engine. The Routing Engine pre-computes backup routes for every MPLS path and provides this information to the Packet Forwarding Engine before any failure. Packet Forwarding Engine local repair is enabled by default and requires no additional configuration.
• Fast reroute—The original control plane method for fast reroute of individual LSPs is described as "one-to-one" protection in the IETF Internet draft Fast Reroute Extensions to RSVP-TE for LSP Tunnels. JUNOS software calculates LSP detours for LSPs and implements the rerouted paths as needed. You can configure the command fast-reroute at the [edit protocols mpls lsp-name] hierarchy level. For more information about MPLS LSP fast reroute, see the JUNOS Internet Software Configuration Guide: MPLS Applications.
• Link protection—This second control plane method is discussed in this guide. In general, link protection is useful when you wish to protect LSPs after a supporting link is lost.