NetworkingA+

Networking Concepts for CompTIA A+ 220-1101

Networking concepts for the CompTIA A+ 220-1101 exam cover the foundational knowledge technicians need to configure, connect, and troubleshoot networks for end users. Unlike the Network+ exam which goes deep into networking, A+ covers practical networking at the technician level — TCP/IP basics, key protocols, IP addressing, and the tools used for day-to-day network support.

8 min

2 sections · 7 exam key points

1 practice questions

TCP/IP Fundamentals

IP addressing: every device on a TCP/IP network needs an IP address, subnet mask, and default gateway. IPv4: 32-bit, written as four octets (192.168.1.100). IPv6: 128-bit, written in hexadecimal groups (2001:db8::1). Subnet mask: defines network vs host portion — /24 (255.255.255.0) means first 24 bits are network, last 8 are hosts. Default gateway: the router's IP — all traffic for other networks goes here.

Private IP ranges (RFC 1918): 10.0.0.0–10.255.255.255, 172.16.0.0–172.31.255.255, 192.168.0.0–192.168.255.255. Not routable on the internet — used on internal networks. APIPA: 169.254.x.x — automatically assigned when DHCP fails. Seeing a 169.254.x.x address is a red flag — check DHCP connectivity.

DHCP: automatically assigns IP address, subnet mask, default gateway, and DNS server to devices. Without DHCP, every device needs manual (static) IP configuration. DHCP lease: temporary assignment, renewed periodically. Command: 'ipconfig /release' then 'ipconfig /renew' (Windows) to get a new DHCP lease.

DNS: translates domain names (www.google.com) to IP addresses. Configured in TCP/IP settings as primary and secondary DNS server IPs. Common DNS servers: Google (8.8.8.8, 8.8.4.4), Cloudflare (1.1.1.1), ISP-provided. DNS test: 'nslookup google.com' — if it returns an IP, DNS works. If it fails but pinging by IP works, DNS is the problem.

Key Protocols and Ports

Protocols A+ technicians must know: HTTP (80 TCP) — web browsing. HTTPS (443 TCP) — secure web. FTP (20/21 TCP) — file transfer. SSH (22 TCP) — secure remote access. Telnet (23 TCP) — insecure remote access. SMTP (25 TCP) — email sending. POP3 (110 TCP) — email retrieval (downloads). IMAP (143 TCP) — email retrieval (sync). DNS (53 UDP/TCP). DHCP (67/68 UDP). RDP (3389 TCP) — Windows Remote Desktop.

TCP vs UDP: TCP is connection-oriented — establishes a connection, ensures delivery, retransmits lost packets. Used for: web browsing, email, file transfers (anything where data integrity matters). UDP is connectionless — send and forget, no retransmission. Used for: DNS, DHCP, streaming, gaming, VoIP (speed matters more than perfection).

Loopback address: 127.0.0.1 (IPv4), ::1 (IPv6) — tests the local TCP/IP stack without going to the network. 'ping 127.0.0.1' — if this fails, TCP/IP stack is corrupted. If this succeeds but pinging the gateway fails, the problem is physical or in the NIC driver.

Key Protocols for CompTIA A+ 220-1101

Protocol	Port	TCP/UDP	Purpose
HTTP	80	TCP	Web pages (unencrypted)
HTTPS	443	TCP	Secure web (TLS)
FTP	20/21	TCP	File transfers
SSH	22	TCP	Secure remote terminal
RDP	3389	TCP	Windows remote desktop
DNS	53	UDP/TCP	Name to IP resolution
DHCP	67/68	UDP	Auto IP assignment
SMTP	25	TCP	Email sending
IMAP	143	TCP	Email sync
POP3	110	TCP	Email download

Key exam facts — A+

APIPA (169.254.x.x): DHCP failed — no connectivity outside local subnet
Default gateway: router IP — devices need this to reach other networks/internet
DNS test: nslookup; IP test: ping 8.8.8.8; stack test: ping 127.0.0.1
TCP: reliable, connection-oriented (web, email); UDP: fast, connectionless (DNS, streaming)
Private IP: 10.x.x.x, 172.16–31.x.x, 192.168.x.x — not internet routable
RDP: port 3389 — Windows Remote Desktop Protocol for remote support
'ipconfig /release' then '/renew': forces new DHCP lease

Common exam traps

If you can ping a website by IP but not by name, the network is broken

If pinging by IP works but pinging by name fails, only DNS is broken — the network itself (routing, physical layer) is working fine. The fix is to check DNS server settings in the IP configuration, not to reinstall network drivers or replace cables

Practice questions — Networking Concepts

These questions are representative of what you will see on A+ exams. The correct answer and explanation are shown immediately below each question.

Q1.A technician runs 'ipconfig' on a Windows computer and sees the IP address 169.254.15.3 with subnet mask 255.255.0.0. What does this indicate?

A.The computer has been assigned a valid static IP address

B.DHCP has failed and the computer has self-assigned an APIPA address

C.The computer is connected to an IPv6 network

D.The computer's network adapter is faulty

Explanation: 169.254.x.x is an APIPA (Automatic Private IP Addressing) address — automatically self-assigned by Windows when DHCP fails. This means the computer cannot reach the DHCP server. The computer can communicate with other APIPA devices on the same segment but cannot reach the internet or other subnets (no gateway or DNS is configured). Troubleshoot DHCP: check cable, verify DHCP server, check DHCP relay agent.

Frequently asked questions — Networking Concepts

What is the difference between POP3 and IMAP for email?

POP3 (Post Office Protocol 3) downloads email from the server to the local device and typically deletes it from the server — email is stored locally only. IMAP (Internet Message Access Protocol) synchronizes email between the server and device — email stays on the server and is synchronized across all your devices. IMAP is preferred for multi-device users (phone + laptop + desktop all see the same inbox). POP3 is simpler but email exists only on the device that downloaded it.

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