7: Upper Layers: Applications, web, http(s), smtp, cloud services.
   Risks: Hacking, app quality, churn.

4. Transport Layer: Segments, TCP/UDP, TLS/SSL, encryption, compression.
   Risks: Poor performance, misconfiguration, key/certificate problems.

3. Network Layer: Packets, routers, IP, routing protocols. 
   Risks: Route disruption/injection, misconfiguration.

2. Data Link Layer: Frames, bridges, switches, interfaces, Ethernet, Wi-Fi security (WPA3!), vLAN documentation. 
   Risks: vLAN confusion, documentation errors.

1. Physical Layer: Bits, cables/fibers, connectors, interfaces. 
   Risks: Break vulnerability, tapping, documentation errors/update.