IS-IS Link-Groups allows the creation of an administrative grouping of multiple IS-IS member interfaces that should be treated as a common group for ECMP purposes. If the number of operational links in the link-group drops below the operational-member value, then all links associated with that IS-IS link group will have their interface metric increased by the configured offset amounts. As a result, IS-IS will then try to reroute traffic over lower cost paths.
After it is triggered, the higher metric will not be reset to the originally configured IS-IS interface metric values until the number of active interfaces in the link bundle reaches the configured revertive threshold (revert-members).
Prerequisite are the following:
one or more interface members
a configured operational-member (oper-members) value
a configured revertive-member (revert-members) value
configured offset values for the appropriate address families