The following describes PCC rules 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 send request messages (PCReq) active VSR-NRC PCE only. Similarly, the PCCs delegate an LSP using a report message (PCRpt) with the Delegate flag set to the active VSR-NRC PCE only. 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 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 returns the delegation of all existing LSPs back to this PCC by sending an empty LSP Update message that has the Delegate flag set as per RFC 8231. To accommodate third party PCE implementations which may not return delegations, each PCC will concurrently revoke the delegation of its LSPs from the current PCE. The PCC will then delegate these LSPs to the new 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 90 seconds) and state timeout timer (default 180 seconds).
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, then by default the PCC clears the LSP state of PCE-initiated LSPs after state timeout expiry; the PCC deletes the PCE-initiated LSPs and releases all their resources. A configuration option of the redelegation timer CLI command allows the user to keep the state of the pce-initiated LSPs instead. The PCC does not clear the state of PCC-initiated LSPs; however, the user can do this by deleting the configuration.