Configuring a Preference Value for IPv6 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 OSPFv3 and IS-IS are configured on a network, the route discovered by OSPFv3 is used because OSPFv3 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 IPv6 IS-IS priority.
1. Access the system view.
  system-view
2. Access the IPv6 IS-IS view.
  isis [ process-id ]
3. Set an IS-IS priority.
  ipv6 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 IPv6 IS-IS route.
1. Access the system view.
  system-view
2. Access the IS-IS process view.
  isis [ process-id ]
3. Set the priority of the specific route through the routing policy.
  ipv6 preference route-policy route-policy-name