Brocade Multi-Service IronWare Routing Configuration Guide (Supporting R05.6.00) - Manual (Page 291)

Multi-Service IronWare Routing Configuration Guide 263
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Globally configuring IS-IS on a device
Changing the SPF timer
Every IS maintains a Shortest Path First (SPF) tree, which is a representation of the states of each
of the IS’s links to ESs and other ISs. If the IS is both a Level-1 and Level-2 IS, it maintains separate
SPF trees for each level.
To ensure that the SPF tree remains current, the IS updates the tree at regular intervals following a
change in network topology or the link state database. By default, the Brocade device recalculates
its IS-IS tree every five seconds following a change. You can change the SPF timer to a value from 1
– 120 seconds.
NOTE
This command has been superseded by the IS-IS PSPF Exponential back-off feature.
To change the SPF interval, enter a command such as the following.
Brocade(config-isis-router)# spf-interval 30
Syntax: [no] spf-interval secs
The secs parameter specifies the interval and can be from 1 – 120 seconds. The default is 5
seconds.
Configuring the IS-IS PSPF exponential back-off feature
The Brocade device uses the exponential back-off mechanism to provide a more responsive
approach to running the PSPF calculations. With this new feature, there is a new configurable
command called partial-spf-interval that allows you to schedule PSPF processing as described in
the following.
An initial-wait interval can be configured as a wait time after an LSP change until the first PSPF
calculation. Optionally, this value is followed by another configurable variable called the
second-wait interval that is used as a wait time between the first and second PSPF calculations.
The second-wait interval (if configured) is then increased in multiples of 2 until it reaches the
maximum hold time as configured by the max-wait variable. Once reached, the maximum hold time
remains the hold interval between PSPF calculations until there are no further changes in the
network. When there are no network changes in a hold down period, the gap between PSPF
calculations returns to the initial-wait interval and the process begins again.
If an initial-wait interval is configured without a second-wait interval, the max-wait variable is used
for the second and all subsequent intervals.
If the initial-wait and second-wait intervals are not configured, the max-wait variable is used for the
first and all subsequent intervals.
The IS-IS PSPF exponential back-off mechanism is configured using the partial-spf-interval
command, as shown in the following.
Brocade(config-isis-router)# partial-spf-interval 60 1000 5000
Syntax: [no] partial-spf-interval max-wait initial-wait second-wait
The max-wait variable specifies the maximum interval between PSPF recalculations. The range of
acceptable values is 0 – 120000 milliseconds. The default is 5000 milliseconds (5 seconds).
The initial-wait variable is an optional value that specifies the wait time after an LSP change until
the first PSPF calculation. The range of acceptable values is 0 – 120000 milliseconds. The default
for this variable is value of the max-wait time.