CompTIA A+ Networking Practice Test: Ports and Subnets

Which ports do I need to know for A+?

The common TCP and UDP ports for file transfer, remote access, email, name resolution, addressing, web, directory and file sharing, and remote desktop.

Ports and protocols for A+ (IANA assignments)
Port	Protocol	Used for
20, 21	FTP	File transfer (data, control)
22	SSH	Encrypted remote command line; SFTP runs over it
23	Telnet	Unencrypted remote command line
25	SMTP	Sending email
53	DNS	Name resolution
67, 68	DHCP	Automatic IP addressing (server, client)
80	HTTP	Web pages, unencrypted
110	POP3	Downloading email
137-139	NetBIOS	Older Windows name and session services
143	IMAP	Email kept on the server
161, 162	SNMP	Network device monitoring (queries, traps)
389	LDAP	Directory services
443	HTTPS	Web pages over TLS
445	SMB	Windows file and printer sharing
3389	RDP	Remote Desktop

Learn them as pairs that go together: 20 and 21 for FTP, 67 and 68 for DHCP, 110 and 143 for receiving mail, 80 and 443 for the web. Also know which use UDP rather than TCP: DNS queries, DHCP and SNMP mostly use UDP.

What do I need to know about IP addressing for A+?

The private IPv4 ranges, APIPA, the default gateway, subnet masks and CIDR, static versus DHCP addressing, and what an IPv6 address looks like.

Addresses worth recognizing (RFC 1918 and RFC 3927)
Range	What it is
10.0.0.0 to 10.255.255.255	Private (10.0.0.0/8)
172.16.0.0 to 172.31.255.255	Private (172.16.0.0/12)
192.168.0.0 to 192.168.255.255	Private (192.168.0.0/16)
169.254.0.0 to 169.254.255.255	APIPA: the PC could not reach a DHCP server
127.0.0.1	Loopback, the computer itself

For subnet questions, count the host bits: 32 minus the prefix. Usable hosts are 2 to the power of the host bits, minus 2. So /24 has 254, /25 has 126, /26 has 62, /27 has 30 and /28 has 14.

Which Wi-Fi standards are on A+?

The 802.11 standards from 802.11a to 802.11ax (Wi-Fi 6 and 6E) and 802.11be (Wi-Fi 7), with their frequency bands, plus the channel and interference basics.

Wi-Fi standards (IEEE and Wi-Fi Alliance names)
Standard	Name	Bands
802.11n	Wi-Fi 4	2.4 and 5 GHz
802.11ac	Wi-Fi 5	5 GHz
802.11ax	Wi-Fi 6 / 6E	2.4 and 5 GHz; 6E adds 6 GHz
802.11be	Wi-Fi 7	2.4, 5 and 6 GHz

What do A+ networking questions look like?

Three examples follow: a subnet count, a blocked-port diagnosis and a Wi-Fi standard. The first is worked in full.

CompTIA A+-style question 1 · Subnetting
How many usable host addresses does a /27 IPv4 subnet provide?
1. A30
2. B32
3. C62
4. D14
Worked answer
A: 30. A /27 leaves 32 − 27 = 5 host bits, which give 2⁵ = 32 addresses. Two are reserved (network and broadcast), so 30 hosts.
1. Host bits: 32 − 27 = 5.
2. Addresses: 2⁵ = 32.
3. Usable: 32 − 2 = 30.
The trap: Answering 32 and forgetting that the network and broadcast addresses cannot be given to hosts.
CompTIA A+-style question 2 · Ports
Users can reach websites by IP address but not by name. A firewall change was made this morning. Which port was most likely blocked?
1. A53
2. B80
3. C443
4. D3389
Show the worked answer
A: 53. Name resolution uses DNS on port 53. Sites load by IP address, so web traffic (80 and 443) is getting through; only the name lookups are failing.
1. By IP works: the web ports are open.
2. By name fails: name resolution is broken.
3. Name resolution is DNS, port 53.
The trap: Choosing 443 because "websites" are failing. If HTTPS were blocked, the IP address would not work either.
CompTIA A+-style question 3 · Wi-Fi standards
Which IEEE standard is marketed as Wi-Fi 6?
1. A802.11ac
2. B802.11ax
3. C802.11n
4. D802.11g
Show the worked answer
B: 802.11ax. 802.11ax is Wi-Fi 6 (and Wi-Fi 6E when it uses the 6 GHz band). 802.11ac is Wi-Fi 5 and 802.11n is Wi-Fi 4.
1. Wi-Fi 4 = 802.11n.
2. Wi-Fi 5 = 802.11ac.
3. Wi-Fi 6 = 802.11ax.
The trap: Picking 802.11ac because it was the fast standard for years. It is Wi-Fi 5.

Make networking automatic

Four Networking drills with new ports and subnets every time, and eight full mocks.

The CompTIA A+ Pass Pack gives you 8 full mocks on the real clock, 36 drills of 12 questions for the sections that cost you points, and a predictor that turns your mocks into the odds of reaching your target. One payment, no subscription, and your free score stays free.

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timed mocks: 36
topic drills: 1
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Which network devices and tools are on A+?

Routers, switches (managed and unmanaged), access points, firewalls, patch panels and PoE, plus the hand tools: crimper, cable tester, toner probe, punchdown tool, Wi-Fi analyzer and loopback plug.

Device questions usually ask which device fits a need: a switch connects devices on one network, a router connects networks, an access point adds wireless, a firewall filters traffic. Tool questions ask which tool finds or fixes a cable problem: a toner probe traces a cable through a wall, a cable tester checks the pairs, a punchdown tool terminates wires in a patch panel.

Network services such as DNS, DHCP, proxy servers and syslog also come up, usually as "which server would do this".

Which network commands should I know for A+?

ipconfig, ping, tracert, nslookup, netstat and pathping on Windows, and ip, ping, traceroute and dig on Linux. Questions describe a problem and ask which command would show the cause.

Network commands and what each shows (our summary)
Command	Shows or does
ipconfig /all	The address, mask, gateway, DNS servers and MAC address
ipconfig /release, /renew	Drops and requests a DHCP address
ping	Whether a host answers, and the round-trip time
tracert (traceroute on Linux)	Each router on the path, to find where traffic stops
nslookup (dig on Linux)	What a DNS server returns for a name
netstat	Open connections and listening ports
pathping	A trace plus packet loss at each hop

A good habit for diagnosis questions is to work outward: ping the loopback (127.0.0.1), then your own address, then the gateway, then an outside address, then an outside name. The first one that fails tells you which layer to fix.

How should I study A+ networking?

Drill the ports daily until they are automatic, practise subnet counts until each takes 20 seconds, and look at your own router's settings to see addressing in practice.

Networking questions also appear in troubleshooting: no internet, intermittent Wi-Fi, an APIPA address. The troubleshooting page covers those. The Core 1 page has the other Core 1 domains, and the full practice test mixes them as the exam does.

Frequently asked questions

How much of A+ is networking?

Networking is 23% of Core 1, and network troubleshooting is part of another 28%.

Do I need to know subnetting for A+?

The basics: CIDR notation, subnet masks and counting hosts. Deeper subnetting is Network+ material.

Which ports are most important?

All the common ones in the table: 20/21, 22, 23, 25, 53, 67/68, 80, 110, 143, 443, 445 and 3389 come up most.

Is IPv6 on A+?

At a basic level: recognizing an IPv6 address and knowing it is 128 bits.

What does a 169.254 address mean?

It is an APIPA address: the computer could not reach a DHCP server and gave itself one.

Which ports use UDP?

DNS queries (53), DHCP (67 and 68) and SNMP (161 and 162) mostly use UDP; most of the others use TCP.

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