When an SR-TE LSP is configured on the router, its path can be computed by the router or by an external TE controller referred to as a PCE. This feature works with the Nokia stateful PCE that is part of the Network Services Platform (NSP).
The 7705 SAR supports three different modes of operation configurable on a per- SR-TE LSP basis.
When the path of the LSP is computed by the router acting as a PCE client (PCC), the LSP is referred to as PCC-initiated and PCC-controlled.
A PCC-initiated and controlled SR-TE LSP has the following characteristics:
can contain strict or loose hops, or a combination of both
does not support CSPF, and local path computation takes the form of hop-to-label translation
has the capability to report an SR-TE LSP to synchronize the LSP database of a stateful PCE server using the pce-report option, but the LSP path cannot be updated by the PCE. The control of the LSP is maintained by the PCC.
When the path of the LSP is computed by the PCE at the request of the PCC, it is referred to as PCC-initiated and PCE-computed.
A PCC-initiated and PCE-computed SR-TE LSP supports the passive stateful mode, which enables the pce-computation option for the SR-TE LSP so that the PCE can perform path computation at the request of the PCC only. The PCC retains control.
The capability exists to report an SR-TE LSP to synchronize the LSP database of a stateful PCE server using the pce-report option.
When the path of the LSP is computed and updated by the PCE following a delegation from the PCC, it is referred to as PCC-initiated and PCE-controlled.
A PCC-initiated and PCE-controlled SR-TE LSP allows active stateful mode, which enables the pce-control option for the SR-TE LSP so that the PCE can perform path computation and updates following a network event without the explicit request from the PCC. The PCC delegates full control.
The user can configure the path computation requests only (PCE-computed) or both path computation requests and path updates (PCE-controlled) to the PCE for a specific LSP using the pce-computation and pce-control commands.
The pce-computation option sends the path computation request to the PCE instead of the local CSPF. When this option is enabled, the PCE acts in passive stateful mode for this LSP. In other words, the PCE can perform path computations for the LSP only at the request of the router. This is used in cases where the operator wants to use the PCE specific path computation algorithm instead of the local router CSPF algorithm.
The default value is no pce-computation. Enabling pce-computation requires that the cspf option also be enabled; otherwise, the command is rejected. If the cspf option is disabled for an LSP, the pce-computation option will also be automatically disabled.
Enabling cspf without enabling pce-computation for an SR-TE LSP means that, internally, the router still performs label translation as if cspf was disabled, because there is no support of CSPF for an SR-TE LSP on the router.
The pce-control option allows the router to delegate full control of the LSP to the PCE (PCE-controlled). Enabling this option means that the PCE is acting in active stateful mode for this LSP and the PCE can reroute the path following a failure or to reoptimize the path and update the router without requiring a request from the router.
The user can delegate CSPF and non-CSPF LSPs.
The user can delegate LSPs that have the pce-computation option enabled or disabled. The LSP maintains its latest active path computed by the PCE or the router at the time it was delegated. The PCE will only make an update to the path at the next network event or reoptimization. The default value is no pce-control.
In all cases, the PCC LSP database is synchronized with the PCE LSP database using the PCEP path computation state report (PCRpt) message for LSPs that have the pce-report command enabled.
The global MPLS- level pce-report command can be used to enable or disable PCE reporting for all SR-TE LSPs for the purpose of LSP database synchronization. This configuration is inherited by all LSPs of a particular type. The PCE reports both CSPF and non-CSPF LSPs. The default value is disabled (no pce-report). This default value controls the introduction of the PCE into an existing network and allows the operator to decide if all LSP types need to be reported.
The LSP-level pce-report command overrides the global configuration for PCE reporting for an LSP. The default value is to inherit the global MPLS-level value. The inherit value reconfigures the LSP to inherit the global configuration for that LSP type.
For more information about configuring PCC-initiated and PCC-controlled LSPs, see Configuring PCC-controlled, PCE-computed, and PCE-controlled SR-TE LSPs.