Thread uses route-over routing as described in the previous section, on 6LoWPAN routing. Up to 32 active routers are allowed in a Thread network. Route traversal is based on next-hop routing. The master route table is maintained by the stack. All routers have an up-to-date copy of the routing for the network. 

Mesh link establishment (MLE) is a method to update path traversal costs from one router to another in a network. Additionally, MLE provides a way to identify and configure neighboring nodes in the mesh and secure them. As a mesh network can expand, shrink, and change shape dynamically, MLE provides the mechanism to reconstitute the topology. MLE exchanges the path costs with all other routers in a compressed format. MLE messages will flood the network in a broadcast manner by the Multicast Protocol for Low Power and Lossy Networks (MPL). 

Typical 802.15.4 networks use on-demand route discovery. This can be costly (bandwidth due to route discovery flooding the network), and Thread attempts to avoid that scheme. Periodically, a Thread network router will exchange MLE advertisement packets with link cost information to its neighbors essentially forcing all routers to have a current path list. If a route terminates (host leaves Thread network) then the routers attempt to find the next best path to a destination. 

Thread also measures the link quality. Remember that 802.15.4 is a WPANs and signal strength may change dynamically. Quality is measured by the link cost of incoming messages for a neighbor with a value of zero (unknown cost) to three (good quality). The following table summarizes the quality to cost relation. This quality and cost are continually monitored and, as mentioned, periodically broadcast to the network for self-healing: