Is-Is And Ospf Support For Loop-Free Alternate Calculation; Figure 27: Topology With Primary And Lfa Routes - Alcatel-Lucent 7210 SAS M User Manual

IS-IS and OSPF Support for Loop-Free Alternate Calculation

SPF computation in IS-IS and OSPF is enhanced to compute LFA alternate routes for each learned
prefix and populate it in RTM.
Figure 27
three routes to reach router R5 from router R1.
The primary route is by way of R3. The LFA route by way of R2 has two equal cost paths to reach
R5. The path by way of R3 protects against failure of link R1-R3. This route is computed by R1 by
checking that the cost for R2 to reach R5 by way of R3 is lower than the cost by way of routes R1
and R3. This condition is referred to as the loop-free criterion. R2 must be loop-free with respect
to source node R1.
7210 SAS M, T, X, R6, Mxp MPLS Configuration Guide
illustrates a simple network topology with point-to-point (P2P) interfaces and highlights
R1
5
5
R3
5
R5
Primary Route
LFA Link-Protect Route
LFA Node-Protect Route

Figure 27: Topology with Primary and LFA Routes

R2
5
5 (8)
R4
5
Label Distribution Protocol
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