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MPLS LSP Link Protection and Node-Link Protection Overview

 

While fast reroute can only protect LSPs on a one-to-one basis, link protection and node-link protection can protect multiple LSPs by using only a single, logical bypass LSP. Link protection can provide robust backup support for a link, node-link protection can bypass a node or a link, and both types of protection are designed to interoperate with other vendor equipment. Such functionality makes link protection and node-link protection excellent choices for scalability, redundancy, and performance in MPLS-enabled networks.

Prior to Junos OS 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.

Scalable solutions for LSP redundancy include link protection and node-link protection. Both approaches are explained in RFC 4090, Fast Reroute Extensions to RSVP-TE for LSP Tunnels. In general, these are facility-based methods that quickly reroute traffic from multiple LSPs. They also reduce the amount of configuration necessary to implement LSP protection.

You can configure either link protection or node-link protection by itself, fast reroute by itself, or both fast reroute and one of the protection methods. Whenever one or more of these reroute options are enabled, Packet Forwarding Engine local repair is activated by default.

To enable Juniper Networks MPLS LSP fast reroute, 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 protection options available in Junos OS 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 but also requires per-packet load-balancing to be configured.

  • 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 OS 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 MPLS Applications Configuration Guide.

  • Link protection—Another control plane method discussed in this guide. In general, link protection is useful when you wish to protect LSPs after a supporting link is lost.

  • Node-link protection—This is also a control plane method and is discussed in this guide. In general, node-link protection is useful when you wish to protect LSPs after a supporting node fails.