Tunnel re-optimization

MPLS TE tunnel re-optimization enables a TE tunnel to be automatically reestablished over new optimal paths when the MPLS network topology changes.

Background

A main function of MPLS TE tunnels is to optimize traffic distribution over a network. Generally, the initial bandwidth of an MPLS TE tunnel is configured based on the initial bandwidth requirement of services, and its path is calculated and set up based on the initial network status. However, a network topology changes in some cases, which may cause bandwidth wastes or require traffic distribution optimization. As such, MPLS TE tunnel re-optimization is required.

Implementation

Tunnel re-optimization allows the ingress to re-optimize a CR-LSP based on certain events so that the CR-LSP can be established over the optimal path with the smallest metric value.

If the fixed filter (FF) resource reservation style is used, tunnel re-optimization cannot be configured.
Tunnel re-optimization is performed based on tunnel path constraints. During path calculation for re-optimization, path constraints, such as explicit path constraints and bandwidth constraints, are also considered.

Re-optimization is classified into the following types based on the triggering mode:

Automatic re-optimization

The ingress automatically triggers CSPF to calculate a path for a tunnel based on the re-optimization interval configured by a network administrator. If the calculated path has a smaller metric than the existing path, a CR-LSP is set up over the new path. If the CR-LSP is successfully set up, the forwarding plane is instructed to switch traffic to the new CR-LSP and delete the original CR-LSP. The re-optimization is then complete. If the CR-LSP is not set up, the traffic is still forwarded along the existing CR-LSP.
Manual re-optimization

The re-optimization command is run in the user view to trigger re-optimization on the tunnel ingress.

The make-before-break mechanism is used to ensure uninterrupted service transmission during the re-optimization process. This means that a new CR-LSP must be established first. Traffic is switched to the new CR-LSP before the original CR-LSP is torn down.