Techniques are disclosed for session-based routing within Open Systems Interconnection (OSI) Model Layer-2 (L2) networks extended over Layer-3 (L3) networks. In one example, L2 networks connect a first client device to a first router and a second client device to a second router. An L3 network connects the first and second routers. The first router receives, from the first client device, an L2 frame destined for the second client device. The first router generates an L3 packet comprising an L3 header specifying L3 addresses of the first and second routers, a first portion of metadata comprising L2 addresses for the first and second client devices, and a second portion of metadata comprising L3 addresses for the first and second client devices, and forwards the L3 packet to the second router. The second router recovers the L2 frame from the metadata and forwards the L2 frame to the second client device.