Resource Cheatsheet
A+ Core 1 2.5: Network Devices
Professor Messer A+ 220-1201 objective 2.5 — routers, managed vs unmanaged switches, access points, patch panels, firewalls, PoE standards, cable/DSL/ONT and NICs.
- Updated
- Reading time
- 6 min read
- Detail
- A+ Core 1
- Detail
- Network Devices
On this page
In one line: every network device has one job and decides using one piece of information — routers use IP addresses, switches and access points use MAC addresses, firewalls use rules — and PoE, modems and ONTs bring power and the internet to it all.
Companion to: Professor Messer, CompTIA A+ 220-1201 Core 1, objective 2.5 (Network Devices). The full version is the Network Devices class notes; the section overview is the Section 2 sheet.
The devices
| Device | Layer | Decides using | Key point |
|---|---|---|---|
| Router | 3 | Destination IP + routing table | Connects subnets, and different media (copper, fibre, wireless, WAN) |
| Layer 3 (multilayer) switch | 2 and 3 | MAC and IP | A switch that also routes |
| Switch | 2 | Destination MAC | Hardware forwarding (ASIC); 24/48 ports, hundreds in the core |
| Access point | 2 | Destination MAC | Bridges wireless to wired: no routing, no address translation |
| Traditional firewall | 3–4 | IP addresses, protocol, ports | Rule-based (ACLs), usually stateful |
| Next-generation firewall | Up to 7 | The application | Can block remote access tools even on port 443 |
A home “wireless router” = router + switch + access point + firewall in one box.
Unmanaged vs managed switches
| Unmanaged | Managed | |
|---|---|---|
| Setup | Plug-and-play | Configured |
| VLANs | None: one big VLAN | Per-port VLANs |
| QoS / prioritisation | No | Yes |
| Redundancy | No | Yes (backup switches) |
| Port mirroring | No | Yes: feed an analyser or IDS |
| SNMP / logs / remote management | No | Yes |
| Price | Low | Higher |
Rule of thumb: if anyone needs to separate, prioritise, monitor or remotely manage traffic, buy managed.
Patch panels
| Part | What happens there |
|---|---|
| Desk → closet run | Permanent; never moved |
| Back of patch panel | Run is punched down (numbered by desk) |
| Front of patch panel | RJ45 socket per desk |
| Patch lead | Short and replaceable: move it to change switch or VLAN |
The lesson’s “punch-down block” and patch panel are one device here: punch-down on the back, RJ45 on the front.
Firewall extras
| Role | Meaning |
|---|---|
| VPN concentrator | Terminates site-to-site and remote access VPNs |
| Proxy | Makes requests for the client, checks responses, then passes them back |
| Router | Routes between subnets, so inter-subnet traffic passes the rules |
Power over Ethernet
| Name | Standard | At the switch (PSE) | At the device (PD) | Max current |
|---|---|---|---|---|
| PoE | 802.3af | 15.4 W | 12.95 W | 350 mA |
| PoE+ | 802.3at | 30 W | 25.5 W | 600 mA |
| PoE++ Type 3 | 802.3bt | 60 W | 51 W | 600 mA per pair set |
| PoE++ Type 4 | 802.3bt | 90 W | 71.3 W | 960 mA per pair set |
| Term | Meaning |
|---|---|
| Endspan | The switch supplies the power |
| Midspan | An injector adds power partway along the cable |
| Backward compatible | A PoE++ switch can power a PoE phone |
| Not forward compatible | A PoE++ device can’t be fully powered by PoE+ |
Uses: PoE — phones · PoE+ — PTZ cameras · PoE++ — high-power APs, some laptops. A switch also has a total PoE budget shared by all ports.
Internet connections
| Device | Medium | Remember |
|---|---|---|
| Cable modem | Coax | DOCSIS; 1 Gb/s+ common; shared with neighbours |
| DSL modem | Telephone line | Asymmetric; slower the further from the exchange or cabinet |
| ONT | Fibre | Optical network terminal; marks the demarc |
| ONT port | Connector | For |
|---|---|---|
| Data | RJ45 | Ethernet to your router |
| Voice | RJ11 | Phones (usually VoIP) |
| Video | F-connector | TV / set-top box |
Demarc: provider’s side = their problem; your side, including internal wiring = yours.
DSL speeds, realistically: ADSL2+ up to ~24 Mb/s down (reach ~5.5 km) · UK FTTC (VDSL2) up to 80/20 Mb/s · 200 Mb/s+ only on the newest VDSL2 over very short lines.
NICs
Built into the motherboard, or added as an expansion card (often 2–4 ports). Match the speed and medium (copper or fibre). Every interface has its own MAC address.
| See MACs | Command |
|---|---|
| PowerShell | Get-NetAdapter |
| Command prompt | getmac /v |
| Linux | ip link |
🔐 Security notes
- Unmanaged switches are blind spots: no logs, VLANs or port security. A hidden desk switch silently extends the LAN.
- Rogue access points: an AP just bridges, so one plugged into a wall socket puts the wired LAN on the air.
- Managed switch hygiene: port security or 802.1X, disable unused ports, management on its own VLAN, SNMPv3 (v1/v2c send community strings in clear text).
- Port mirroring feeds IDS and packet capture.
- Firewall as router makes inter-subnet traffic a filtered, logged chokepoint; NGFWs catch apps hiding on port 443.
- Lock wiring closets: whoever reaches the patch panel can move any desk onto any network.
- PoE devices are IoT: put cameras, phones and APs on their own VLANs.
- Your side of the demarc is yours: change default credentials on ISP-supplied kit.
Practice drills
1. A router forwards by what, and at which layer?
The destination IP address, using its routing table, at layer 3.
2. A small office wants guest devices kept off the staff network on the same switch. Managed or unmanaged?
Managed. Separation on one switch needs VLANs, which unmanaged switches don’t have.
3. What makes an access point different from a SOHO wireless router?
An AP only bridges wireless to wired, forwarding by MAC address. It does no routing or address translation.
4. A firewall blocks remote access software over HTTPS but allows web browsing. What type is it?
A next-generation firewall. It identifies the application, not just the port.
5. The switch has no PoE, but a ceiling AP needs power. What do you use, and what's it called?
A PoE injector: a midspan arrangement. PoE from the switch itself is endspan.
6. How much power does PoE+ provide at the switch and at the device?
30 W at the switch, 25.5 W at the device.
7. Which device converts the provider's fibre to Ethernet, and what does it mark?
The ONT (optical network terminal). It marks the demarcation point.
8. A server has a four-port NIC. How many MAC addresses does it have?
Four: one per interface.
Key takeaways
- Routers use IP addresses (layer 3); switches and APs use MAC addresses (layer 2).
- Managed switches add VLANs, QoS, redundancy, port mirroring and SNMP; unmanaged switches add nothing but ports.
- Patch panels keep permanent runs fixed; move patch leads, not cables.
- PoE 15.4 W · PoE+ 30 W · PoE++ 60/90 W at the switch; endspan = switch, midspan = injector.
- Cable = coax/DOCSIS · DSL = phone line, distance-limited · ONT = fibre, at the demarc.