📘 01-04: Network Hardware Devices¶
📌 Common Devices and Their Roles¶
| Device | OSI Layer | Function |
|---|---|---|
| NIC | 1–2 | Connects a host to the medium; has a burned-in MAC address |
| Hub | 1 | Repeats signals out all ports (single collision domain) — legacy |
| Switch | 2 | Forwards frames by MAC address; each port = own collision domain |
| Router | 3 | Forwards packets between networks using IP; separates broadcast domains |
| Layer 3 switch | 2–3 | Switches and routes between VLANs at wire speed |
| Access Point (AP) | 1–2 | Bridges wireless clients to the wired LAN |
| Firewall | 3–7 | Filters traffic by policy between network zones |
📌 Hub vs. Switch vs. Router¶
- Hub — "dumb" repeater; everyone hears everything. Causes collisions. Obsolete.
- Switch — learns MAC addresses, builds a MAC table, and forwards frames only to the correct port. Each port is its own collision domain.
- Router — connects different networks (LAN ↔ Internet), makes path decisions using IP, and does not forward broadcasts.
📌 Collision vs. Broadcast Domains¶
| Collision domain | Broadcast domain | |
|---|---|---|
| Hub | One (all ports) | One |
| Switch | One per port | One (per VLAN) |
| Router | One per interface | One per interface |
- Switches break up collision domains.
- Routers (and VLANs) break up broadcast domains.
📌 The NIC¶
- Provides the host's physical connection (Layer 1) and its MAC address (Layer 2).
- Can be wired (Ethernet) or wireless (Wi-Fi).
Tip
Key idea — Switches move frames within a network (Layer 2); routers move packets between networks (Layer 3). Switches break up collision domains; routers break up broadcast domains.
See also: The OSI Model, Network Segmentation
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