4Infrastructure

• 4.1Status lights and ports

  Covers what the color and solid/blinking state of a switch or router link light (LED) mean, and the roles of each port—console port, serial port, Ethernet port, fiber/SFP, USB port, and PoE—as the foundation for "reading a device's state from its lights alone" and "telling which socket to plug into."

• 4.2Cabling from a network diagram

  Covers wiring patch cables correctly per an engineer's network diagram, a small topology including a switch and router, and the layout of the rack that houses the gear (rack units (U), cable management, power via a PDU, and a UPS), as the introductory task of "cabling exactly as the diagram shows, in order, down to the power."

• 4.3Basic routing concepts

  Covers the default gateway as the exit when leaving your own network (to another network), the difference between an L2 switch (forwarding within one segment by MAC) and an L3 switch (which can also route between networks), and how forwarding changes by whether the destination is on the local network or a remote network—as the foundation for telling "does this destination go via the gateway or arrive directly."

• 4.4Basic switching concepts

  Covers the MAC address table by which a switch learns a source MAC and its receive port, flooding for unknown/broadcast frames, the default 300-second aging, MAC address filtering for permit control, and the VLAN that divides an L2 broadcast domain—learned while glancing at show mac address-table as the basics of "how a switch learns and delivers to a destination."