OSI Model

Network communication happens in seven layers. Each layer has a specific job and only needs to care about the layers directly above and below it.

Traffic Types (How Data Moves)

Our design heavily targets Layer 2 (L2) and Layer 3 (L3).

• Layer 2 (Data Link - "The Same Room"): This is traffic between devices on the same network segment using physical MAC addresses. It is handled by switches. Think of it as talking to someone in the same room. It is extremely fast because it happens entirely in hardware.
• Layer 3 (Network - "Different Cities"): This is traffic between different network segments using IP addresses. It is handled by routers. Think of it as mailing a letter to another city; it must go through a post office (the router) to find its way. This often requires CPU cycles.

Example: When your Proxmox EPYC Node (10.0.10.20) talks to your Proxmox Ryzen Node (10.0.10.21) on the same VLAN, that is L2 traffic. It never touches the router CPU. When your EPYC Node (10.0.10.20) talks to a container in the Client VLAN (10.0.40.50), that is L3 traffic. It must go to the router (default gateway) to be routed across VLANs.

Layers Working Together

Here is what the stack looks like when a browser request leaves your machine and is unpacked on the server.

The important practical point is that failures usually map to a layer. A DNS issue is not the same class of problem as a dropped TCP connection or a broken cable.