2.2 - Switches, MAC addresses and PoE
CompTIA A+ Core 1 objective 2.2 covers common networking hardware. A switch forwards frames only to the port of the destination device, using the MAC address - the Layer 2 identifier burned into each network interface. When a switch does not supply Power over Ethernet, a PoE injector adds power onto the Ethernet cable to run a device like an IP camera. On 2.4 GHz Wi-Fi, only channels 1, 6 and 11 do not overlap, so two nearby access points should use a plan such as channels 1 and 6 to avoid interference. Expect scenario questions that describe forwarding by MAC, powering a device over Ethernet, or fixing 2.4 GHz interference, and ask which device or channel plan is correct.
Forward frames by MAC to one port = switch. Layer 2 hardware address = MAC. Add power on Ethernet = PoE injector. Non-overlapping 2.4 GHz channels = 1, 6, 11 (use 1 and 6).
Practice questions
1. Two access points on the 2.4 GHz band keep interfering. Which channel plan avoids overlap?
- Channels 2 and 3
- Channels 4 and 8
- Channels 1 and 6 (correct answer)
- Channels 9 and 10
On 2.4 GHz, only channels 1, 6 and 11 don't overlap. Picking 1 and 6 avoids co-channel interference.
2. Which uniquely identifies a network interface at Layer 2 and is burned into the hardware?
- IP address
- MAC address (correct answer)
- Hostname
- Subnet mask
A MAC address (48-bit, hex) is the hardware/Layer-2 identifier of a NIC; IP is the logical Layer-3 address.
3. Which networking device forwards frames only to the port of the destination MAC?
- Hub
- Switch (correct answer)
- Repeater
- Modem
A switch learns MAC addresses and forwards frames only to the correct port; a hub floods all ports.
4. Which device injects power into an Ethernet cable to run a PoE camera when the switch isn't PoE?
- A signal repeater
- A PoE injector (correct answer)
- A broadband modem
- A patch panel
A PoE injector adds power to the Ethernet run so a PD (camera/AP/phone) works without a PoE switch.
5. Which passive device organizes and terminates many horizontal cable runs in a rack?
- Router
- Patch panel (correct answer)
- Firewall
- Load balancer
A patch panel terminates cable runs and lets you patch them to switch ports with short patch cables — clean cable management.
6. Which device can enforce VLANs, port security and QoS on its ports?
- Unmanaged switch
- Managed switch (correct answer)
- Hub
- Repeater
A managed switch supports configuration (VLANs, port security, QoS, monitoring); unmanaged switches just forward.