This task explains
how to make adjustments to the SPF calculation to tune router performance. This
task is optional.
Because the SPF
calculation computes routes for a particular topology, the tuning attributes
are located in the router address family configuration submode. SPF calculation
computes routes for Level 1 and Level 2 separately.
When IPv4 and IPv6
address families are used in a single-topology mode, only a single SPF for the
IPv4 topology exists. The IPv6 topology “borrows” the IPv4 topology; therefore,
no SPF calculation is required for IPv6. To tune the SPF calculation parameters
for single-topology mode, configure the
address-family ipv4 unicast command.
The incremental SPF
algorithm can be enabled separately. When enabled, the incremental shortest
path first (ISPF) is not employed immediately. Instead, the full SPF algorithm
is used to “seed” the state information required for the ISPF to run. The
startup delay prevents the ISPF from running for a specified interval after an
IS-IS restart (to permit the database to stabilize). After the startup delay
elapses, the ISPF is principally responsible for performing all of the SPF
calculations. The reseed interval enables a periodic running of the full SPF to
ensure that the iSFP state remains synchronized.