The Rbridge concept was introduced by Radia Perlman in her famous paper "Rbridges: Transparent Routing". Rbridges combine the transparency and self-configuration typical of the data-link layer to the packet routing that normally occur at the inter-networking layer. For this reason Rbridges have been defined as devices working at the second and a half layer. Vtrill is an implementation of Rbridges for VDE, a proof-of-concept of the Rbridge definition applied to virtual networking.