There are several methods of protecting traffic when using MPLS, including options to protect a single link, an entire node, or the entire path.
The Resource Reservation Protocol (RSVP) provides a way to define MPLS paths across a network. RSVP includes mechanisms to specifically define which nodes the path traverses. You can do this manually, specifying each hop, or you can configure parameters such as bandwidth and link color, and let the router dynamically define certain parts of the path based on resource availability.
RSVP is responsible for signaling the MPLS path—that is, establishing and setting it up. It is also responsible for monitoring the path once it has been established. Traditional RSVP failure detection mechanisms are quite slow, on the order of several seconds to detect failures. However, additions to the original protocol provide a detection mechanism that can offer subsecond failover. This feature is called fast reroute (FRR).
Fast reroute provides failure detection and recovery in an incredible 50 ms. That’s the same failover time as APS for SONET networks!
FRR is a mechanism that establishes detour label-switched paths (LSPs) at each router along the main MPLS LSP. If a node or link fails, the upstream router immediately sends traffic to its detour LSP. The router also notifies the ingress router for the path that part of the main LSP has failed. The ingress router can then redirect traffic along a new LSP as appropriate. This ...