Configuring CSPF
Constrained Shortest Path First (CSPF) is configured to calculate the shortest path destined for a specified node.
Context
CSPF is configured on all nodes along a path to enable the ingress to calculate a complete path.
CSPF calculates only the shortest path to the specified tunnel destination. During path computation, if there are multiple paths with the same weight, the optimal path is selected using the tie-breaking function.
The tie-breaking function is performed in one of the following modes:
Most-fill: The device selects a link with the largest ratio of used bandwidth to maximum reservable bandwidth. This mode enables the device to effectively use bandwidth resources.
Least-fill: The device selects a link with the smallest ratio of used bandwidth to maximum reservable bandwidth. This mode enables the device to evenly use bandwidth resources on links.
Random: The device selects a link at random. This mode allows CR-LSPs to distribute evenly over links, regardless of bandwidth.
The Most-fill and Least-fill modes are only effective when the difference in bandwidth usage between the two links exceeds 10%, such as 50% of link A bandwidth utilization and 45% of link B bandwidth utilization. The value is 5%. At this time, the Most-fill and Least-fill modes do not take effect, and the Random mode is still used.
Procedure
- Run system-view
The system view is displayed.
- Run mpls
The MPLS view is displayed.
- Run mpls te cspf
CSPF is enabled on the local node.
- (Optional) Run mpls te cspf preferred-igp { isis [ process-id [ level-1 | level-2 ] ] | ospf [ process-id [ area area-id ] ] }
A preferred IGP is configured. Its process and area or level can also be configured.
- (Optional) Run mpls te cspf multi-instance shortest-path [ preferred-igp { isis | ospf } [ process-id ] ]
CSPF is configured to calculate shortest paths among all IGP processes and areas.
The mpls te cspf multi-instance shortest-path command is mutually exclusive with the mpls te cspf preferred-igp command. If the mpls te cspf multi-instance shortest-path command is run, this command overrides the mpls te cspf preferred-igp command.
- Run mpls te tie-breaking { least-fill | most-fill | random }
A tie-breaking mode for calculating a path for a CR-LSP is specified.
- (Optional) Run mpls te cspf optimize-mode disable
The optimization mode is disabled when CSPF calculates the path.
CSPF provides a method for selecting a path in the MPLS domain. By default, the optimization mode is used for path calculation, and the path calculation is performed from Egress to Ingress. Compared with the common calculation method, the optimization mode has higher efficiency.
The mpls te cspf optimize-mode disable command is used to disable the CSPF optimization mode. After the configuration, the path is calculated from Ingress to Egress.
- Run quit
The system view is displayed.
- Run interface tunnel tunnel-number
The view of the MPLS TE tunnel interface is displayed.
- Run mpls te tie-breaking { least-fill | most-fill | random }
The tie-breaking function for calculating a path is configured for the current tunnel.
The tie-breaking mode is configured either the tunnel interface view or MPLS view. If the tie-breaking mode configured in both the tunnel interface and MPLS views, the configuration in the tunnel interface view takes effect.
- Run commit
The configurations are committed.