The following describes rules for a PCC with PCE redundancy:
PCCs can establish upstream PCEP sessions with at most two VSR-NRC PCEs.
Each upstream session has a preference that takes effect when both upstream PCEP sessions are successfully established. The PCE peer that is not in overload is always selected by the PCC as the active PCE. However, if neither of the PCEs are signaling the overload state, the PCE with the higher numerical preference value is selected, and in case of a tie, the PCE with the lower IP address is selected.
In the steady state, because one upstream VSR-NRC PCE is in overload, only one PCEP session is active. The PCCs delegate an LSP using a report message (PCRpt) with the Delegate flag set to the active VSR-NRC PCE only. Request messages (PCReq) are not sent to the secondary/standby VSR-NRC PCE in overload. PCRpt messages are sent with the Delegate flag clear to the secondary/standby VSR-NRC PCE in overload.
If the current active PCEP session signals the overload state, the PCC will select the other PCE as the active PCE as long as the corresponding PCEP session is not in overload. Any new path request message (PCReq) or path report message (PCRpt) with the Delegate flag set is sent to the new PCE.
The PCE in overload should return the delegation of all existing LSPs to this PCC by sending an empty LSP Update Request that has the Delegate flag set as per RFC 8231. This PCC will then delegate these LSPs to the newly active PCE by sending a path report (PCRpt) with the Delegate flag set.
If the current active PCEP session goes operationally down, the PCC starts the redelegation timer (default is 90 s).
If the PCEP session is restored before the redelegation timer expires, no delegation change is performed and the LSP state is maintained.
Upon expiration of the redelegation timer, the PCC looks for the other PCEP session and, if not in overload, it immediately delegates the LSPs to the newly active PCE. If the new PCE accepts the delegation, the LSP state is maintained.
If the PCEP session does not recover before the redelegation timer expires and the PCC fails to find another active PCEP session, the state of LSPs by default are not cleared. The PCC does not clear the state of PCC-initiated LSPs; however, the user can do this by deleting the configuration.