This document describes a mechanism to reduce redundant packet transmissions for the IS-IS Routing protocol, as described in ISO 10589 [1]. The described mechanism can be used to reduce the flooding of Link State PDUs (LSPs) in IS-IS topologies. The net effect is to engineer a flooding topology for LSPs which is a subset of the physical topology. This draft serves to document the existing behavior in deployed implementations. The draft describes changes to implementations, not to the protocol. These changes are backwards compatible with implementations that do not support this feature.