Holds the primary routing metric of this alternate path to the destination, with -1 used when the metric is unknown. Admins compare this against the primary route's metric to judge how much longer or costlier traffic would travel if fast-reroute activates this backup, which matters for capacity planning during a failure. An alternate path reporting ipFrrAltMetric1 far higher than the primary route's metric warns an admin that, while fast-reroute would keep traffic flowing, it might take a much less efficient path during a failover.