Configuring an IS-IS Link Group

If one of the links that are load-balancing traffic fails, traffic may get lost. To prevent traffic loss, configure an IS-IS link group.

Usage Scenario

A link group is a group of links that are used for load balancing. If a link failure occurs and the bandwidth of the other links in the group is not sufficient enough to carry the traffic, the link group automatically increases the link cost so that the routes along its member links are not selected. Then, traffic is switched to a backup link, which prevents traffic loss. If the link failure is cleared, the link group can automatically restore the original link cost. After the link cost is restored, routes are recalculated, and traffic is then forwarded along the optimal route.

Pre-configuration Tasks

Before configuring an IS-IS link group, configure basic IPv4 IS-IS functions or basic IPv6 IS-IS functions.

Procedure

Run system-view
The system view is displayed.
Run isis [ process-id ]
The IS-IS view is displayed.
Run link-group group-name
A link group is created, and the link group view is displayed.
Run cost-offset { cost | max-reachable | maximum }
A link cost offset is configured.

If maximum is specified in the command, the maximum value (16777215) is used as the link cost of the member links, and the routes along these links are used to transmit TE information, not selected for traffic forwarding.
Run min-members min-num
A minimum number of member links is specified. If the number of available member links in the link group falls below min-num, the configured link cost offset is added to the link cost of these member links.
Run revert-members revert-num
A number is specified. After the number of available member links in the link group reaches or exceeds revert-num the original link cost of these member links is restored.

The value of revert-number must be greater than or equal to that of min-number.
Run quit
Exit from the link group view.
Run quit
The IS-IS view is displayed.
Run interface interface-type interface-number
The interface view is displayed.
Run isis link-group group-name [ level-1 | level-2 ]
The interface is bound to the link group.

To bind multiple interfaces to the link group, repeat Steps 9 and 10.
Run commit
The configuration is committed.

Checking the Configurations

An IS-IS link group has been configured.

Run the display isis link-group [process-id ][group-name ] command to check information about an IS-IS link group.
Run the display isis link-group interface interface-type interface-number command to check information about the link group to which the interface has been bound.