RSVP LSP Optimization
Optimizing RSVP LSPs
RSVP LSPs can automatically find and signal better, more optimal paths, but this is not by default.
By default, RSVP LSPs stay on their path until they are torn down or preempted. They wont change even if a better path becomes available.
This default behaviour can be changed with LSP optimization which runs CSPF at regular intervals (specified by the opimization timer).
We can enable optimization globally or on individual LSPs. Both methods make use of the optimize-timer statement.
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root@juniper# set protocols mpls optimize-timer <value>
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root@juniper# set protocols mpls label-switched-path <lsp-name> to X.X.X.X optimize-timer <value>
The default value for optimize-timer is 0 seconds, which means optimization never happens.
We can also optimize manually, with the clear mpls lsp name <lsp-name> optimize command. Traffic moves to new paths gracefully.
Conditions for LSP optimization
- The new CSPF metric must not be higher than the old path
- If the metrics are same, the new path must not have more hops
- The new path must not cause preemption of other LSPs
- The new path must not worsen the congestion overall
Large topologies benefit from shorter optimize-timers but more frequent opitimiztion increses the CPU usage.
If we want to optimize purely on IGP metric (condition 1 above) and ignore the remaining all conditions (condition 2, 3, and 4), we can specify optimize-aggressive either globally or on individual LSP.
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root@juniper# set protocols mpls optimize-aggressive
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root@juniper# set protocols mpls label-switched-path <lsp-name> to X.X.X.X optimize-aggressive
We can also optimize-aggressivemanually, with the clear mpls lsp name <lsp-name> optimize-aggressive command.
Also, we can optimize detour and bypass LSPs, both configured under edit protocols rsvp.
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root@juniper# set protocols rsvp fast-reroute optimize-timer <value>
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root@juniper# set protocols rsvp interface <interface-name> link-protection optimize-timer <value>
