Configuring IPv4 IS-IS Route Selection

Configuring IS-IS route selection can achieve refined control over route selection.

Usage Scenario

After basic IPv4 IS-IS functions are configured, IS-IS routes will be generated, enabling communication between different nodes on a network.

If multiple routes are available, the route discovered by IS-IS may not be the expected one, which does not meet network planning requirements nor facilitate traffic management. To address this issue, configure IPv4 IS-IS route selection to implement refined control over route selection.

To implement refined control over IPv4 IS-IS route selection, perform the following operations:

Configure the costs for IPv4 IS-IS interfaces.

Changing the IS-IS cost for an interface can control route selection, but routes on the interface need to be recalculated if a network topology changes, especially on a large-scale network. In addition, the configuration result may not meet your expectation.

Therefore, configure IS-IS costs before configuring basic IS-IS functions.
Configure IPv4 IS-IS route leaking.
Configure rules for selecting equal-cost IPv4 IS-IS routes.
Filter IPv4 IS-IS routes.
Configure an overload bit for an IPv4 IS-IS device.
Configure an IPv4 IS-IS interface to automatically adjust the link cost.

Pre-configuration Tasks

Before configuring IPv4 IS-IS route selection, complete the following tasks:

Configure IP addresses for interfaces to ensure that neighboring nodes are reachable at the network layer.
Configure basic IPv4 IS-IS functions.

Configuring IPv4 IS-IS Route Leaking: Configuring IS-IS route leaking enables you to optimize IS-IS route selection on a two-level-area network.

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.

Filtering IPv4 IS-IS Routes: If some IS-IS routes are not preferred, configure conditions to filter IS-IS routes. Only IS-IS routes meeting the specified conditions can be added to an IP routing table.

Configuring an Overload Bit for an IPv4 IS-IS Device: If an IS-IS device needs to be temporarily isolated, configure the overload state for it to prevent other devices from forwarding traffic to this IS-IS device and prevent routing black holes.

Configuring IS-IS to Generate IPv4 Default Routes: This section describes how to configure IS-IS to generate default routes to control the advertising of IS-IS routing information.

Configuring an IPv4 IS-IS Interface to Automatically Adjust the Link Cost: Configuring an IS-IS interface to automatically adjust the link cost based on link quality facilitates route selection control and improves network reliability.

Verifying the IPv4 IS-IS Route Selection Configuration: After configuring IPv4 IS-IS route selection, check the configurations.