Specifying The Spf Interval - Juniper IGP - CONFIGURATION GUIDE V11.1.X Configuration Manual

max-lsp-lifetime

Specifying the SPF Interval

You can configure how often the router performs the shortest-path-first (SPF)
calculation. IS-IS runs SPF calculations in response to any change in its link-state
database. Because SPF calculation is processor intensive, increasing the SPF interval
reduces the processor load of the router, but can slow down the rate of convergence.
Topology changes in a network cause all routers involved in the change to regenerate
their LSDB and flood new LSPs throughout the network. Therefore, a router that
receives a new LSP is likely to receive more LSPs in the following seconds. An
immediate response to a given change is going to miss the subsequent topology
changes and spend CPU time. When many changes are taking place, a slower
response to each change makes more sense.
IS-IS enables the router to respond quickly to an isolated network event, but to slow
the response exponentially when many triggering events are taking place in rapid
succession. SPF calculations are performed at exponentially increasing intervals until
the maximum interval set by the spf-interval command is reached.
The first SPF calculation is performed immediately when the LDSB changes. If another
calculation-triggering event occurs, the router waits 1 second before performing the
SPF calculation. If another event occurs, the router waits 2 seconds before performing
the SPF calculation. The interval between a triggering event and the corresponding
SPF calculation continues to increase exponentially: 4 seconds, 8 seconds, 16 seconds,
Increasing the interval reduces the link utilization caused by the flooding of
refreshed packets.
Example
host1(config-router)#lsp-refresh-interval 1000
Use the no version to restore the default value, 900 seconds.
See lsp-refresh-interval
Use to set the maximum time that LSPs persist without being refreshed.
You can select a maximum time in the range 1–65535 seconds.
The default value is 1200 seconds (20 minutes).
You might need to adjust the maximum LSP lifetime if you change the LSP refresh
interval with the lsp-refresh-interval command. The maximum LSP lifetime
must be greater than the LSP refresh interval.
Example
host1(config-router)#max-lsp-lifetime 1500
Use the no version to restore the default value, 1200 seconds.
See max-lsp-lifetime
Chapter 6: Configuring IS-IS
Configuring Global IS-IS Parameters
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