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JUNOS Cookbook by Aviva Garrett

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14.12. Using Fast Reroute to Reduce Packet Loss Following a Link Failure

Problem

You want to reduce packet loss when a link along an LSP fails.

Solution

Fast reroute reduces packet loss when a link in the LSP fails. You configure fast reroute on the ingress router only:

	[edit protocols mpls]
	aviva@R1# set label-switched-path R1-to-R5 to 10.0.0.5
	aviva@R1# set label-switched-path R1-to-R5 fast-reroute

Discussion

A basic function of IP routing protocols is to reroute traffic changes that occur in the network, such as a link or router node failure. Because the IP routing protocols are distributed across the network devices and because all routers must have a consistent view of the network, it can take some time for the routes to converge after a topology change. In a large network, convergence times can be on the order of several seconds, which may be unacceptable for your service-level agreements (SLAs).

MPLS fast reroute provides a solution to the convergence problem by rerouting traffic around a point of failure in an LSP. Fast reroute sets up a protection LSP around a point of failure in advance to protect an individual link between two routers. Each router in the LSP sets up protection LSPs when the ingress router signals the initial setup of the LSP. When a link along an LSP fails, the router upstream of the failure switches to the protection LSP as soon as it detects the failure. No route calculations need to be done because the protection LSP is signaled and set up in advance, ...

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