Configuring a Preference Value for IS-IS

If multiple routes to the same destination are discovered by different routing protocols, configuring the highest preference value for IS-IS allows a route discovered by IS-IS to be selected preferentially.

Context

If multiple routes to the same destination are discovered by different routing protocols running on the same device, the route discovered by the protocol with the highest preference is selected.

For example, if both OSPF and IS-IS are configured on a network, the route discovered by OSPF is used because OSPF has a higher preference than IS-IS by default.

To prefer a route discovered by IS-IS, configure a higher preference value for IS-IS. In addition, a routing policy can be configured to increase the preferences of specified IS-IS routes, without affecting route selection.

Procedure

Configure IS-IS priority.
1. Access the system view.
  system-view
2. Access the IS-IS process view.
  isis [ process-id ]
3. Set the IS-IS priority.
  preference preference
  
  One router can run multiple routing protocols at the same time. When multiple routing protocols discover routes to the same destination, the route discovered by the protocol with the highest priority is selected.
  
  This command is used to configure the priority of the IS-IS routing protocol. The smaller the value is, the higher the priority is.
  
  By default, the priority of IS-IS is set to 15.
Configure the priority of the specific IS-IS route.
1. Access the system view.
  system-view
2. Access the IS-IS process view.
  isis [ process-id ]
3. Configure the priority of the specific route through the routing policy.
  preference route-policy route-policy-name