Configuration Considerations When Using CSPF Fate-Sharing Group Information

Consider the following when using CSPF fate-sharing group information:

Note

This release only supports a single mode of CSPF computation for a CSPF group by adding penalties to each TE link's native IGP cost when it shares fate-sharing groups used by the protected path.

• CSPF computation using a CSPF group is only applicable when computing a secondary LSP path. It is not applicable to the primary or protected LSP path.
• CSPF calculates the least cost paths first and then applies the hop limit on the paths.
• CSPF computation using a CSPF group is used only for computing the secondary LSP path when the primary LSP is in an UP state. In this case, CSPF collects group information from all TE links used by the primary LSP. For each TE link, CSPF computes the total adjusted distance. The total adjusted distance for each TE link is equal to the native IGP cost of the TE link plus the sum of all penalties of the CSPF groups that the TE link is associated with, and used by the primary LSP. For example, Q1, Q2, and Q3 is a collection of CSPF groups used by the primary LSP. TE link 1 is a member of CSPF groups Q1 and Q2. Q1 has a penalty of 10, and Q2 has a penalty 30. The total penalty of CSPF groups Q1 and Q2 is equal to 40. The total adjusted distance for TE link 1 is equal to the native IGP cost plus 40. The penalty is only applied once to each shared CSPF group that the TE link is associated with. The secondary LSP path is then computed from ingress to egress using the adjusted distance of each TE link.