Configuring Equal-Cost IS-IS Routes

Context

If there are redundant IS-IS links, multiple routes may have an equal cost. Choose either of the following methods to use these equal-cost IS-IS routes:

Configure load balancing for equal-cost IS-IS routes so that traffic will be evenly balanced among these links.

This mechanism increases the link bandwidth usage and prevents network congestion caused by link overload. However, this mechanism may make traffic management more difficult because traffic will be randomly forwarded.
Configure preference values for equal-cost IS-IS routes so that only the route with the highest preference will be used and the others function as backups.

This configuration facilitates traffic management and improves the network reliability, without the need to change original configurations.

Procedure

Configure equal-cost IS-IS routes to work in load-balancing mode.
1. Run system-view
  The system view is displayed.
2. Run isis [ process-id ]
  The IS-IS view is displayed.
3. Run maximum load-balancing number
  The maximum number of load-balancing equal-cost IS-IS routes is set.
  
  By default, the maximum number of equal-cost routes on the S5720I-SI, S5720S-SI, S5720-SI, S5735-S, S5735S-S, S5735-S-I, S5730S-EI, S5730-SI, S6720S-SI, or S6720-SI is 8, and the maximum number of equal-cost routes on the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, or S6730S-S is 16.
  When the number of equal-cost routes is larger than the value specified in the maximum load-balancing command, valid routes are selected for load balancing based on the following criteria:
  Route preference: Routes with lower preference values (higher preferences) are selected for load balancing.
  Next hop system ID: If routes have the same preference, routes with smaller system IDs are selected for load balancing.
  Interface index: If routes have the same preference and system ID, routes with lower interface index values are selected for load balancing.
Configure preference values for equal-cost IS-IS routes.
1. Run system-view
  The system view is displayed.
2. Run isis [ process-id ]
  The IS-IS view is displayed.
3. Run nexthop ip-address weight value
  A preference value is configured for an equal-cost IS-IS route.
  
  By default, the preference value configured for equal-cost IS-IS routes is 255. A smaller value indicates a higher priority.