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MPLS Fast Reroute provides a mechanism for automatically
rerouting traffic on an LSP if a node or link in the
LSP fails.
Fast rerouting is accomplished by pre-computing and
pre-establishing a number of "protection LSPs"
between the source and destination routers. Each link
or node in an MPLS network can be protected via a protection
LSP. This LSP provides an alternative path (detour)
for the data being sent through primary LSPs that pass
through the link or node should there be a failure.
The LSP acts as a temporary tunnel through which all
of the affected LSPs can be routed. The fall-over mechanisms
are triggered by physical link or routing events that
indicate that the link or node is down. In theory, a
router should be able to reroute packets immediately
after receiving the event. Ideally there should be no
packet loss or interrupted services during the switchover.
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Network Services 
