The following secondary to primary path reversion is supported for RSVP-TE LSPs:
Configurable timer-based reversion for primary LSP path
Manual reversion from secondary to primary path
Normally, an RSVP-TE LSP automatically switches back from using a secondary path to the primary path as soon as the primary path recovers. In some deployments, it is useful to delay reversion or allow manual reversion, instead of allowing an LSP to revert to the primary path as soon as it is available. This feature provides a method to manage fail-overs in the network.
If manual reversion is used, a fall-back timer-based mechanism is required in case a human operator fails to execute the switch back to the primary path. This function is also useful to stagger reversion for large numbers of LSPs.
A reversion timer for an LSP is configured using the CLI as follows:
config
router
[no] mpls
lsp
[no] revert-timer <timer-value>
When configured, the revert timer is started as soon as a primary path recovers. The LSP does not revert from the currently used secondary path to the primary path until the timer expires. When configured, the revert-timer is used instead of the existing hold timer.
The timer value can be configured in one minute increments, up to 4320 minutes (72 hours). After a timer has started, it can be modified using this command. If a new value is entered, then the current timer is canceled (without reverting the LSP) and then restarted using the new value. The revert timer should always be configured to a higher value than the hold timer. This prevents the router from reverting to the primary path and sending traffic before the downstream LSRs have programmed their data path.
The no form of the command cancels any currently outstanding revert timer and causes the LSP to revert to the primary path if it is up.
If the LSP secondary path fails while the revert timer is still running, the system cancels the revert-timer and the LSP reverts to the primary path immediately. A user can manually force an LSP to revert to the primary path while the revert-timer is still running, using the following tools command:
tools>perform>router>mpls revert lsp lsp-name
This command forces the early expiry of the revert timer for the LSP. The primary path must be up in order for this command to work.