Study Hub / CompTIA A+ (220-1201 & 220-1202) / 1101 · Domain 2.0
CompTIA A+ (220-1201) Domain 2.0: Networking — Explained
Domain 2.0 is practical networking for the technician: the ports and protocols you'll see on the job, setting up small-office networks, Wi-Fi that actually works, and the cables and connectors in your toolkit.
Ports and protocols: the working set
- Web and file transfer — HTTP 80, HTTPS 443, FTP 20/21, SFTP 22 (SSH-based), TFTP 69 (trivial, no auth — PXE boot and phone configs).
- Email — SMTP 25 (sending), IMAP 143 (reading, mail stays on server), POP3 110 (reading, mail downloads). Encrypted variants add 465/993/995.
- Network services — DNS 53 (names), DHCP 67/68 (addresses), SSH 22 (secure remote), RDP 3389 (Windows remote desktop), SNMP 161/162 (monitoring), LDAP 389 (directory).
- TCP vs. UDP — TCP is reliable and ordered (web, email, file transfer — "must arrive"); UDP is fast and connectionless (DNS, DHCP, streaming, VoIP — "arrive fast, loss is tolerable"). The protocol fits the need.
SOHO networks and Wi-Fi
- The SOHO router does everything — modem/gateway, DHCP server, DNS forwarder, NAT, firewall, Wi-Fi access point. One box, five jobs — which is why "restart the router" fixes so much.
- Wi-Fi standards — 802.11n (Wi-Fi 4), ac (Wi-Fi 5), ax (Wi-Fi 6/6E) — each generation faster and better at crowded airspace. 2.4 GHz reaches farther; 5/6 GHz is faster but shorter-range.
- Wi-Fi security — WPA2-Personal minimum (AES), WPA3 where available; WEP and WPA are broken — never deploy. Change default admin credentials and SSIDs on day one.
- Channels — 2.4 GHz: use only 1, 6, or 11 (non-overlapping). Auto-channel usually works; manual assignment fixes neighbor interference.
- Common SOHO fixes — no internet: check modem lights → router → DHCP lease → DNS. Slow Wi-Fi: channel congestion, distance, or an ancient 802.11n client dragging the cell down.
Cabling and connectors
- Twisted pair — Cat5e (1 Gbps), Cat6 (10 Gbps short runs), Cat6a (10 Gbps full 100m). RJ45 connectors; T568A/B wiring standards — both ends the same for straight-through (device-to-switch), different for crossover (rare now; auto-MDIX handles it).
- Fiber — single-mode (long distance, laser, yellow jacket) vs. multimode (shorter, LED, orange/aqua). LC and SC connectors dominate; ST is legacy. Fiber = distance + immunity to interference.
- Coax and legacy — RG-6 (cable modem/satellite, F-connectors), RG-59 (older CCTV). Know them on sight; you'll still meet them in the field.
- Tools — cable tester (continuity/wiring), tone generator + probe (find the cable in the wall), crimper, punch-down tool (110 block). Test every run you terminate.
The must-memorize table: essential ports
The ports the exam asks about most.
| Port(s) | Service | TCP/UDP |
|---|---|---|
| 20/21 | FTP | TCP |
| 22 | SSH / SFTP / SCP | TCP |
| 25 | SMTP (sending mail) | TCP |
| 53 | DNS | Both |
| 67/68 | DHCP | UDP |
| 80 / 443 | HTTP / HTTPS | TCP |
| 110 / 143 | POP3 / IMAP (receiving mail) | TCP |
| 161/162 | SNMP | UDP |
| 389 | LDAP | TCP |
| 3389 | RDP | TCP |
Try it: 4 sample questions
Sample questions to check your understanding of this domain. Answers and full reasoning are tucked under each one.
1. A user can ping 8.8.8.8 but no website loads by name. Which service and port are implicated?
- A. A. DHCP on UDP 67/68
- B. B. DNS on port 53 — name resolution is failing while IP connectivity works
- C. C. HTTPS on TCP 443
- D. D. SMTP on TCP 25
Show answer & reasoning
B. "IPs work, names don't" is the DNS signature: ping proves Layer 3; dead names prove resolution failed. Check the DNS server settings (often DHCP-provided) before touching anything else. Port 53, both TCP and UDP.
2. A small office needs Wi-Fi for 15 laptops with the best security available on modern hardware. Which standard and encryption?
- A. A. 802.11n with WEP
- B. B. 802.11ax (Wi-Fi 6) with WPA3
- C. C. 802.11g with WPA
- D. D. Open network — fastest
Show answer & reasoning
B. Current-generation Wi-Fi (ax/Wi-Fi 6) with WPA3 is the modern answer: best performance in crowded airspace and the strongest available encryption. WEP (A) is cracked in minutes; WPA (C) is deprecated; open (D) is an invitation. Also change the router's default admin credentials.
3. A technician must run network 90 meters to a new office and needs 10 Gbps. Which cable?
- A. A. Cat5e
- B. B. Cat6a — rated for 10 Gbps at the full 100m
- C. C. RG-6 coax
- D. D. Any Cat5 will do
Show answer & reasoning
B. Cat6a carries 10 Gbps to 100 meters; Cat6 only manages 10 Gbps on short runs (~55m); Cat5e tops out at 1 Gbps. At 90m needing 10 gig, Cat6a is the correct call — or fiber for longer/future-proofing. Match the cable to distance and speed.
4. Email sends fine but the user can't receive new messages on a newly configured client. Which ports/protocols should the technician verify?
- A. A. SMTP port 25 only
- B. B. The receiving protocol in use — IMAP 143 or POP3 110 (and their TLS variants 993/995)
- C. C. DNS port 53
- D. D. FTP ports 20/21
Show answer & reasoning
B. Sending = SMTP (works); receiving = IMAP or POP3 — the broken half. Verify the client is configured for the right receive protocol, port, and encryption matching the provider. SMTP (A) is already proven working; DNS (C) would break sending too. Split the problem by direction.
This was one domain. The simulator drills all 9.
This free preview covered 1101: Networking (2.0, 23%). Not covered here: 1101: Hardware (3.0, 25%); 1101: Hardware & Network Troubleshooting (5.0, 28%); 1102: Software Troubleshooting (3.0, 21%). The three troubleshooting and hardware domains — the most scenario-heavy A+ material — stay in the paid guide and practice bank. The ByteBar Practice Exam Simulator drills every domain with 1,000 exam-style questions — $9.99 one-time unlocks all 28 exams. Prefer to read? The full A+ Study Guide is in the ByteBar shop on Etsy.
Practice Exam Simulator — $9.99 one-time, all 28 exams Full Study Guides on Etsy