Configuring Rules for Selecting Equal-Cost IPv4 IS-IS Routes

If multiple equal-cost IS-IS routes are available on a network, configure the equal-cost IS-IS routes to load-balance traffic to increase the bandwidth usage of each link, or configure priorities for the equal-cost IS-IS routes to facilitate traffic management.

Context

If there are multiple IS-IS routes with the same cost, choose either of the following methods to use these equal-cost IS-IS routes:

Configure load balancing for equal-cost IS-IS routes.

Load balancing increases the link bandwidth usage and prevents network congestion caused by link overload. However, Load balancing may complicate traffic management because traffic will be randomly forwarded.
Configure priorities for equal-cost IS-IS routes so that only the route with the highest priority is preferentially selected, and the others function as backups.

The original configurations do not need to be changed. This method facilitates traffic management and improves the network reliability.

Procedure

Configure load balancing 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 maximum load-balancing number
  The maximum number of equal-cost IS-IS routes for load balancing is set.
  If the actual equal-cost routes outnumber the value specified in the maximum load-balancing command, routes are selected for load balancing based on the following rules:
  Route preference: Routes with lower preference value (higher preference) are selected for load balancing. For details about route preference configuration, see Configure priorities for equal-cost IS-IS routes.
  Next hop System ID: If routes have the same priorities, routes with smaller System ID are selected for load balancing.
  Interface index: If routes have the same priorities and System ID, routes with lower interface index values are selected for load balancing.
4. (Optional) Run ecmp-prefer [ te-tunnel | intact ]
  The priority is set for the routes with a TE tunnel interface or an IPv4 interface as the outbound interface.
  
  If both an IGP-Shortcut-enabled TE tunnel and IP link are available, you can configure priorities for the routes with a TE tunnel interface or an IPv4 interface as the outbound interface for route selection.
5. Run commit
  The configuration is committed.
Configure priority 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 priority is configured for an equal-cost IS-IS route.
  
  A smaller value of the value parameter indicates a higher priority.
4. Run commit
  The configuration is committed.