Huawei Alibaba Huawei When the Intermediate System to Intermediate System (IS-IS) routing protocol is adopted by a highly symmetric network such as the Leaf- Spine or Fat-Tree network, the Leaf nodes (e.g., Top of Rack switches in datacenters) are recommended to be prevented from receiving other nodes' explicit routes in order to achieve scalability. However, such a setup would cause traffic black-holes or suboptimal routing if link failure happens in the network. This document introduces INFINITE cost to IS-IS LSPs to solve this problem.