Local protection attempts to address the disadvantages of path protection by focusing on a single resource at a time (link or node), in contrast to path protection which attempts to provide protection for the entire path from the ingress router to the egress router. Double-booking of resources, unnecessary protection and nondeterministic switchover times are the main disadvantages of path protection, arising from protection at the ingress router for the entire path. By providing focused protection from the ingress of a single resource at a time, local protection addresses the disadvantages of path protection, minimizing the amount of time during which traffic is lost, while utilizing resources efficiently.
In Figure 4, if the LSP from R1 to R5 fails on the link between R2 and R4, a detour or bypass path is pre-established quickly, and traffic is redirected around the failure, until the ingress router moves the LSP to a new path that does not use the failed link.
In the Juniper Networks implementation, local protection methods are defined by the number of LSPs protected by the backup path. When one LSP is protected by one backup path, the backup path is referred to as a detour and the protection method is called fast reroute (one-to-one backup). When many LSPs are protected by one backup path, the backup path is referred to as a bypass and the protection method is called facility backup. The purpose of facility backup is to protect a link or node (facility). Facility backup can be used for protecting either a link or a node (and its associated links), also referred to as node-link protection.
The following local protection methods are discussed in this section: