A MPLS CSPF fate-sharing group or a Shared Risk Link Group (SRLG) is a method used to group Traffic Engineering (TE) links and nodes in a network that share the same risk of failure. The user can influence the path computation for a CSPF-enabled LSP by configuring a CSPF fate-sharing group so that both the protected path and the backup path avoid sharing the same TE links traversed. The path computation for a CSPF-enabled LSP uses the information from the TE database to compute the best path for an LSP satisfying all constraints (bandwidth reservations, network topology information, available resources), yet has the shortest distance to its destination. The CSPF computation for an LSP only uses the information from the TE database at the time of computation. Any future updates to the TE database do not cause the CSPF-enabled LSP to recompute. Each CSPF fate-sharing group has an associated penalty (or cost) assigned to it. The penalty associated with a CSPF fate-sharing group is used to direct the path computation for a CSPF-enabled LSP away from TE links that share the same risk used by the set of TE links that the protected path is using. The greater the penalty associated with a group, the less likely the secondary shares TE links used by the protected path.
A CSPF fate-sharing group is identified by a group name, and uses the following four ways to identify elements in the TE database:
A CSPF fate-sharing group can be used for setting up a secondary LSP when the associated primary LSP is in an UP state.
Refer to Configure an MPLS CSPF Fate-Sharing Group for more information on configuring the path computation for a CSPF-enabled LSP using CSPF fate-sharing group information.