MPLS-Enabled Applications: Emerging Developments and New Technologies

3.5. LOCAL PROTECTION USING FAST REROUTE

The goal of protection is to minimize the time during which traffic is lost. Thus, it makes sense to apply protection as close to the point of failure as possible. The idea of local protection is simple. Instead of providing protection at the head end for the entire path, the traffic around the point of failure is rerouted. This is very similar to what happens when the highway between two cities closes somewhere between exits A and B. Rather than redirecting all the traffic away from the highway altogether, vehicles are directed on to a detour path at exit A and rejoin the highway at exit B or at some other exit down the road from B.

The use of a detour is a very intuitive concept, easily applicable to TE LSPs, as shown in Figure 3.2 An alternate path, called the detour or bypass, is created by R1 (the 'Point of Local Repair' or PLR for short) in order to avoid the link R1-R2. In case of a failure, traffic is shuttled around the failed link using this path and rejoins the LSP at R2 (the 'Merge Point' or MP for short). Thus, the traffic is quickly rerouted around the point of failure and for this reason this mechanism is called fast reroute. The idea is not to keep the traffic on the detour until the link recovers, but rather to keep it long enough for the LSP head end to move the LSP to a new path that does not use the failed link. There are several attractive properties to fast reroute:

Figure 3.2. Fast reroute using local protection ...