1. A method implemented by a network device in a network having a plurality of nodes, the method to compute a loop free alternative (LFA) next hop as a backup for a primary path next hop for an interior gateway protocol (IGP), where the method enables an administrator to control LFA selection for a destination node using a tag and a weight, the method comprising the steps of: selecting a next candidate node from a set of neighbor nodes in the network to perform LFA computation; determining whether an interface of the next candidate node towards a source node provides an LFA for the destination node; checking whether the interface of the next candidate node has a tag with a tag value matching a tag value of a primary SPF path for the destination node; checking whether the destination node has any LFA; checking whether a stored tag differs from the tag value of the primary SPF path for the destination node; checking whether the interface of the next candidate node is preferred based on a comparison of a weight value of the interface of the next candidate node and a stored weight; replacing a stored LFA for the destination node with the next candidate node, a stored weight with a weight of the interface of the next candidate node, and a stored tag with a tag of the interface of the next candidate node; and downloading the stored LFA to a global routing information base after all candidate nodes have been exhausted.