The technology disclosed herein enables an L3 network fabric including one or more spine switches having a leaf-spine topology to be self-expanded. In a particular embodiment, a method provides transferring one or more probe messages from each of the spine switches. The probe messages detect whether new computing nodes have been attached to the communication network. The method further provides receiving a reply to at least one of the probe messages. The reply identifies a new computing node that is not yet included in the L3 fabric. In response to the reply, the method provides confirming physical network interfaces of the spine switches indicate valid connections to one or more new leaf switches of the new computing node, using L3 discovery protocols to ensure the connections conform to the leaf-spine topology, and transferring probe packets between the spine switches and leaf switches, including the new leaf switches, of computing nodes connected thereto to confirm configuration of all connections between the spine switches and the leaf switches of the computing nodes. Moreover, the method provides configuring L3 protocols for routing communications exchanged with the new computing node.