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 non-session-based L2 frame destined for the second client device. The first router forms an L3 packet comprising an L3 header specifying L3 addresses of the first and second routers and a protocol selected based on an L3 service for the L2 frame, a payload comprising the L2 frame, and metadata comprising a session identifier distinctly identifying the L2 frame, and forwards the L3 packet to the second router. The second router recovers the L2 frame from the payload and forwards the L2 frame to the second client device.