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Controlling SPF calculation interval
Based on the LSDB, an IS-IS router uses the SPF algorithm to calculate the shortest path tree with itself
being the root, and uses the shortest path tree to determine the next hop to a destination network. By
adjusting the SPF calculation interval, you can prevent bandwidth and router resources from being over
consumed due to frequent topology changes.
When network changes are not frequent, the minimum-interval is adopted. If network changes become
frequent, the SPF calculation interval is incremented by incremental-interval × 2
n-2
(n is the number of
calculation times) each time a calculation occurs until the maximum-interval is reached.
To control SPF calculation interval:
Ste
Command
Remarks
1. Enter system view.
system-view N/A
2. Enter IS-IS view.
isis [ process-id ] [ vpn-instance
vpn-instance-name ]
N/A
3. Configure the SPF
calculation interval.
timer spf maximum-interval
[ minimum-interval [ incremental-interval ] ]
By default:
• The maximum interval is 5
seconds.
• The minimum interval is 50
milliseconds.
• The incremental interval is
200 milliseconds.
Configuring convergence priorities for specific routes
A topology change causes IS-IS routing convergence. To improve convergence speed, you can assign
convergence priorities to IS-IS routes. Convergence priority levels are critical, high, medium, and low. The
higher the convergence priority, the faster the convergence speed.
By default, IS-IS host routes have medium convergence priority, and other IS-IS routes have low
convergence priority.
To assign convergence priorities to specific IS-IS routes:
Ste
Command
Remarks
1. Enter system view.
system-view N/A
2. Enter IS-IS view.
isis [ process-id ] [ vpn-instance
vpn-instance-name ]
N/A
3. Assign convergence priorities
to specific IS-IS routes.
priority { critical | high | medium }
{ prefix-list prefix-list-name | tag
tag-value }
By default, IS-IS routes, except IS-IS
host routes, have the low
convergence priority.
Setting the LSDB overload bit
By setting the overload bit in sent LSPs, a router informs other routers of failures that make it unable to
select routes and forward packets.
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