Overview
Networking is Core 1 (220-1201) domain 2.0 and carries 23% of that exam across eight objectives. It covers TCP and UDP ports and protocols, wireless technologies (2.4, 5 and 6 GHz bands, 802.11 standards, Bluetooth, NFC, RFID), the services networked hosts provide, DNS records and DHCP scopes, networking hardware including Power over Ethernet (PoE), small office/home office (SOHO) addressing, internet connection and network types, and hand tools such as crimpers, toner probes and cable testers.
Candidates must be able to read a symptom like a 169.254.x.x address or a mail server that rejects messages and connect it to the right service or setting. The domain feeds directly into Core 1 objective 5.5 (troubleshoot network issues) and Core 2 objectives on Windows networking, SOHO security and remote access.
How it's tested
Expect a blend of recall and scenario reasoning. Some items ask directly which port or record type serves a purpose; others describe a user who cannot reach a share, a printer that needs a fixed address, or an office choosing an internet link. Performance-based items may ask you to match ports to protocols or set up a SOHO router.
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Port and protocol match
A service is described by what it does (encrypted remote shell, secure web, Windows file sharing) and you pick the protocol and port, or the reverse.
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Read the address
An IP address, mask or gateway is given and you infer the cause, such as 169.254.x.x meaning the client never reached a DHCP server.
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Pick the device or link
An office needs to segment traffic, power a camera, or connect a rural site, and you choose between switch, router, PoE, VLAN, fiber, cable, satellite or WISP.
A new desk phone and a ceiling access point must be installed where there is no electrical outlet, and the switch is an unmanaged model without PoE. The phrase no outlet signals Power over Ethernet, and the switch detail rules out powering from the switch. The best answer is a PoE injector between the switch and each device, not a new circuit or a wireless bridge.
Objectives 8
Official objectives from the CompTIA outline, in outline order.
2.1 Compare and contrast Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) ports, protocols, and their purposesThe well-known ports and whether each service rides TCP or UDP.
- What it means
- Covers FTP 20/21, SSH 22, Telnet 23, SMTP 25, DNS 53, DHCP 67/68, HTTP 80, POP3 110, NetBIOS/NetBT 137-139, IMAP 143, LDAP 389, HTTPS 443, SMB/CIFS 445 and RDP 3389, plus the difference between connection-oriented TCP and connectionless UDP.
- What to understand
- TCP uses a three-way handshake, sequencing and acknowledgments for reliable delivery, while UDP sends without setup for speed and low overhead. DHCP is UDP; DNS uses UDP for most queries and TCP for zone transfers and large responses; most other listed services use TCP. Know which are insecure plaintext (Telnet, FTP, HTTP, POP3 and IMAP without TLS) and their secure replacements.
- How it shows up
- A firewall rule, a mail client setup or a remote access request names a function and you choose the port, or a port is listed and you name the service.
- Common confusion
- Swapping 110 and 143, or 137-139 and 445. POP3 is 110 and IMAP is 143; NetBIOS uses 137-139, while modern SMB runs directly on 445.
2.2 Explain wireless networking technologiesBands, channels, 802.11 standards, Bluetooth, NFC and RFID.
- What it means
- Covers the 2.4 GHz, 5 GHz and 6 GHz bands, channel selection, channel width and regulatory limits, the 802.11a/b/g/n/ac/ax family, and short-range technologies (Bluetooth, NFC, RFID).
- What to understand
- 2.4 GHz reaches farther and penetrates walls better but is crowded, with only channels 1, 6 and 11 non-overlapping in North America at 20 MHz width. 5 GHz and 6 GHz offer more channels and speed at shorter range; 6 GHz requires Wi-Fi 6E (802.11ax) or Wi-Fi 7 hardware. Wider channels (40, 80, 160 MHz) raise throughput but reduce the number of non-overlapping channels.
- How it shows up
- A user in a dense apartment block gets slow Wi-Fi, or an older device cannot see a network, and you pick the band, channel or standard that explains it.
- Common confusion
- Believing 5 GHz always performs better. Through several walls or at long range, 2.4 GHz can deliver a more usable signal.
2.3 Summarize services provided by networked hostsServer roles, internet appliances and embedded systems.
- What it means
- Covers server roles (DNS, DHCP, file share, print, mail, syslog, web, AAA, database, NTP), internet appliances (spam gateways, unified threat management, load balancers, proxy servers), and legacy or embedded systems such as SCADA and IoT devices.
- What to understand
- Know what each role does in one line: syslog centralizes logs, NTP keeps clocks in sync (which Kerberos and log correlation depend on), AAA handles authentication, authorization and accounting, a load balancer spreads requests across servers, and a proxy makes requests on clients' behalf and can filter or cache. UTM combines firewall, intrusion prevention, antivirus and content filtering in one box.
- How it shows up
- An office wants one device for several security functions, or needs logs collected centrally, and you choose the matching service or appliance.
- Common confusion
- Mixing up a proxy and a load balancer. A proxy acts for clients going out; a load balancer distributes incoming requests across servers.
2.4 Explain common network configuration conceptsDNS record types, mail authentication, DHCP options, VLANs and VPNs.
- What it means
- Covers DNS records (A, AAAA, CNAME, MX, TXT), the TXT-based mail authentication records DKIM, SPF and DMARC, DHCP leases, reservations, scopes and exclusions, virtual LANs (VLANs) and virtual private networks (VPNs).
- What to understand
- A maps a name to IPv4, AAAA to IPv6, CNAME is an alias to another name, MX names the mail server for a domain, TXT holds text such as SPF (which servers may send mail), DKIM (a public key for signature checks) and DMARC (what receivers do when SPF or DKIM fails). A DHCP reservation always hands the same address to a given MAC address; an exclusion keeps a range out of the pool for static devices.
- How it shows up
- Outbound mail is marked as spam, a printer needs a predictable address, or departments must be separated on one switch, and you choose the record, DHCP option or VLAN.
- Common confusion
- Treating a reservation and an exclusion as the same thing. A reservation is a DHCP-assigned fixed address; an exclusion stops DHCP from handing out addresses you will set manually.
2.5 Compare and contrast common networking hardware devicesRouters, switches, access points, firewalls, PoE and edge devices.
- What it means
- Covers routers, managed and unmanaged switches, access points, patch panels, firewalls, PoE injectors, PoE switches and standards, cable modems, DSL modems, optical network terminals (ONTs) and network interface cards with their physical MAC addresses.
- What to understand
- A switch forwards frames by MAC address within a network; a router forwards packets between networks by IP address. Managed switches add VLANs, port monitoring and configuration; unmanaged switches are plug-and-play. PoE delivers power over data cabling: 802.3af up to 15.4 W per port, 802.3at (PoE+) up to 30 W, and 802.3bt for higher loads. An ONT terminates fiber at the customer premises.
- How it shows up
- An office needs VLANs, power for cameras, or to connect to a fiber provider, and you choose the device.
- Common confusion
- Choosing an unmanaged switch when the scenario requires VLANs. Only managed switches can configure VLANs.
2.6 Given a scenario, configure basic wired/wireless small office/home office (SOHO) networksIPv4 and IPv6 addressing, APIPA, static vs. dynamic, masks and gateways.
- What it means
- Covers IPv4 private and public addressing, IPv6, Automatic Private IP Addressing (APIPA), static versus dynamic assignment, subnet masks and default gateways in a small office or home network.
- What to understand
- Private IPv4 ranges are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16, translated to a public address by the router's NAT. APIPA addresses in 169.254.0.0/16 mean the client asked for DHCP and got no answer. Servers, printers and network gear get static or reserved addresses; ordinary clients use DHCP. The gateway must be on the client's own subnet.
- How it shows up
- A client has 169.254.x.x, or can reach local hosts but not the internet, and you identify the missing DHCP, wrong gateway or wrong mask.
- Common confusion
- Assuming APIPA means the network cable is unplugged. A link exists; the client simply could not reach a DHCP server.
2.7 Compare and contrast internet connection types, network types, and their characteristicsSatellite, fiber, cable, DSL, cellular and WISP; LAN through SAN.
- What it means
- Covers internet connection types (satellite, fiber, cable, DSL, cellular, wireless internet service provider or WISP) and network types (LAN, WAN, PAN, MAN, SAN, WLAN).
- What to understand
- Fiber offers the highest speeds and symmetric options; cable is shared among neighbors on a coaxial segment; DSL runs on telephone lines and slows with distance from the provider; geostationary satellite has high latency, while low Earth orbit satellite service reduces it considerably; WISP uses fixed outdoor wireless links. A SAN is a dedicated storage network, not a geographic size.
- How it shows up
- A remote site, a latency-sensitive application or a budget is described and you pick the connection type, or a scope is described and you name the network type.
- Common confusion
- Treating SAN as a size like LAN or MAN. It is a purpose-built network for block storage.
2.8 Explain networking tools and their purposesCrimpers, strippers, testers, toner probes, punchdown tools, loopback plugs and taps.
- What it means
- Covers the crimper, cable stripper, Wi-Fi analyzer, toner probe, punchdown tool, cable tester, loopback plug and network tap.
- What to understand
- Crimpers attach RJ45 connectors, punchdown tools seat wires into patch panels and keystone jacks, a toner probe traces an unlabeled cable to its port, a cable tester checks continuity and pinout, a loopback plug tests a NIC or switch port by sending its signal back, a Wi-Fi analyzer shows channels and signal strength, and a tap copies traffic for monitoring.
- How it shows up
- A technician must find which patch panel port a wall jack uses, or verify a new cable, and you choose the tool.
- Common confusion
- Picking a cable tester to locate an unlabeled cable. Locating is the toner probe's job; the tester confirms wiring once you have both ends.
High-yield concepts
The terms, rules and formulas this domain turns into questions most often.
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Well-known ports
FTP 20/21, SSH 22, Telnet 23, SMTP 25, DNS 53, DHCP 67/68, HTTP 80, POP3 110, NetBIOS 137-139, IMAP 143, LDAP 389, HTTPS 443, SMB 445, RDP 3389.
- Remember
- Group them by job: remote access (22, 23, 3389), mail (25, 110, 143), web (80, 443), file sharing (20/21, 137-139, 445), infrastructure (53, 67/68, 389).
- Tested as
- Directly tested and reused in firewall and troubleshooting scenarios.
- Trap
- Choosing Telnet 23 when the scenario requires an encrypted command-line session, which is SSH 22.
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TCP vs. UDP
TCP sets up a session and guarantees ordered delivery; UDP sends datagrams with no handshake or retransmission.
- Remember
- DHCP and most DNS queries use UDP; file transfer, web, mail and remote sessions use TCP.
- Tested as
- Asked as a comparison and inside port questions.
- Trap
- Thinking UDP is unreliable and therefore never used for important services.
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APIPA (169.254.0.0/16)
The address Windows assigns itself when it requests DHCP and receives no reply.
- Remember
- An APIPA address means the client can talk only to other APIPA hosts on the same segment and cannot reach the gateway or internet.
- Tested as
- One of the most common clues in network troubleshooting questions.
- Trap
- Replacing the NIC when the real fault is a down DHCP server, exhausted scope or wrong VLAN.
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Private IPv4 ranges
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are reserved for internal networks and are not routed on the internet.
- Remember
- SOHO routers use NAT to translate these to one public address.
- Tested as
- Address-type questions and SOHO setup.
- Trap
- Calling 172.32.x.x private; the range stops at 172.31.255.255.
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DNS record types
A (IPv4), AAAA (IPv6), CNAME (alias), MX (mail server), TXT (text including SPF, DKIM and DMARC).
- Remember
- MX tells senders where to deliver mail for a domain; TXT records carry the mail authentication policies.
- Tested as
- Mail delivery and spam scenarios.
- Trap
- Choosing an A record to fix mail routing instead of the MX record.
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SPF, DKIM and DMARC
SPF lists servers allowed to send for a domain, DKIM publishes a key to verify message signatures, DMARC tells receivers how to handle failures and where to report.
- Remember
- All three are published as DNS TXT records and work together to reduce spoofing.
- Tested as
- A company's mail is landing in spam or being spoofed.
- Trap
- Thinking DMARC encrypts mail; it only sets policy and reporting.
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DHCP reservation vs. exclusion
A reservation always gives one MAC address the same IP; an exclusion removes addresses from the pool.
- Remember
- Use a reservation to keep DHCP management of a printer's address; use an exclusion for devices configured statically.
- Tested as
- Printer or server addressing scenarios.
- Trap
- Setting a static IP inside the active scope without an exclusion, which causes conflicts.
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802.11 standards and bands
802.11b/g use 2.4 GHz; a and ac use 5 GHz; n uses 2.4 and 5 GHz; ax (Wi-Fi 6/6E) uses 2.4, 5 and 6 GHz.
- Remember
- A device can join a 6 GHz network only if it supports Wi-Fi 6E or later.
- Tested as
- Compatibility and band-selection questions.
- Trap
- Expecting an 802.11ac-only client to connect to a 2.4 GHz network; ac radios are 5 GHz, though most such devices also include an older 2.4 GHz radio.
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Non-overlapping 2.4 GHz channels
In North America only channels 1, 6 and 11 avoid overlap at 20 MHz width.
- Remember
- In crowded areas, move to a less congested channel among these or to 5 or 6 GHz.
- Tested as
- Interference and slow Wi-Fi scenarios.
- Trap
- Choosing channel 3 or 9, which overlap neighbors on both sides.
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Power over Ethernet
Delivers DC power over twisted-pair cabling to devices such as phones, cameras and access points.
- Remember
- 802.3af supplies up to 15.4 W per port, 802.3at (PoE+) up to 30 W, 802.3bt more; use an injector if the switch lacks PoE.
- Tested as
- Installing devices where there is no outlet.
- Trap
- Assuming any switch provides power on its ports.
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VLAN
A logical network created on managed switches that separates traffic as if the ports were on different switches.
- Remember
- Moving between VLANs requires a router or Layer 3 switch.
- Tested as
- Separating guest, voice or departmental traffic.
- Trap
- Thinking VLANs encrypt traffic; they segment it.
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Toner probe
A tone generator on one end of a cable and an inductive probe that beeps near the matching cable at the other end.
- Remember
- It finds a cable; it does not verify pinout or performance.
- Tested as
- Tool-selection questions in wiring closets.
- Trap
- Choosing a cable tester or loopback plug to locate the cable.
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Satellite latency
Geostationary satellites orbit about 35,786 km up, adding hundreds of milliseconds of round-trip delay.
- Remember
- Low Earth orbit services cut latency substantially but still depend on line of sight to the sky.
- Tested as
- Choosing a link for a remote site with voice or video needs.
- Trap
- Recommending geostationary satellite for latency-sensitive applications when another option exists.
Side by side
Concepts candidates mix up, compared on the point that decides the answer.
Switch vs. router vs. access point
| Concept | Meaning | Key difference | Common trap |
|---|---|---|---|
| Switch | Connects devices within one network and forwards frames by MAC address. | Works inside a LAN; managed models add VLANs. | Expecting it to route between subnets or provide internet access by itself. |
| Router | Forwards packets between networks using IP addresses; SOHO models add NAT, DHCP and firewall. | Connects different networks, such as the LAN to the internet. | Choosing a router when the requirement is simply more wired ports. |
| Access point | Bridges wireless clients onto the wired network. | Adds Wi-Fi coverage; does not route on its own. | Confusing a standalone AP with a SOHO wireless router that combines all three roles. |
POP3 vs. IMAP vs. SMTP
| Concept | Meaning | Key difference | Common trap |
|---|---|---|---|
| SMTP (25) | Sends mail from client to server and between servers. | Outbound delivery only. | Choosing SMTP for a client that cannot download mail. |
| POP3 (110) | Downloads mail to one client, usually removing it from the server. | Poor for users on several devices. | Recommending POP3 when mail must stay in sync across phone and laptop. |
| IMAP (143) | Keeps mail on the server and syncs folders and read status across clients. | Best for multi-device access. | Mixing up its port with POP3's 110. |
Fiber vs. cable vs. DSL vs. satellite
| Concept | Meaning | Key difference | Common trap |
|---|---|---|---|
| Fiber | Light over glass to an ONT. | Highest speeds, low latency, immune to EMI. | Assuming it is available everywhere. |
| Cable | Coaxial cable TV infrastructure with a cable modem. | Fast but shared with neighbors on the segment. | Expecting consistent speed at peak hours. |
| DSL | Data over telephone copper. | Speed drops with distance from the provider's equipment. | Ignoring distance limits in a rural scenario. |
| Satellite | Radio link to orbiting satellites. | Available almost anywhere; geostationary adds high latency. | Choosing it for real-time voice when cable or fiber is available. |
Exam traps
Each trap is an answer that looks right. Learn the clue that should change your mind.
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Insecure protocol picked for a secure need
- What candidates pick
- Telnet on port 23 for remote router administration.
- Why it looks right
- Telnet is the classic remote command-line protocol.
- Why it's wrong
- Telnet sends credentials in plaintext; SSH on port 22 provides the same function encrypted.
Clue to watch for The scenario says secure, encrypted or across an untrusted network.
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APIPA blamed on hardware
- What candidates pick
- Replace the network card on a PC showing 169.254.12.5.
- Why it looks right
- The PC clearly cannot reach the network.
- Why it's wrong
- APIPA proves the NIC works and has a link; the client did not get a DHCP response, so check the DHCP server, scope, relay or VLAN.
Clue to watch for An address in 169.254.0.0/16.
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A record for mail delivery
- What candidates pick
- Update the domain's A record when inbound mail is not arriving at the new mail server.
- Why it looks right
- A records map names to addresses, which seems like the fix.
- Why it's wrong
- Senders look up the MX record to find a domain's mail server; the MX must point to the new server's host name.
Clue to watch for The problem is specific to incoming email for the domain.
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5 GHz as the universal fix
- What candidates pick
- Move a client in a far bedroom to 5 GHz to improve its weak signal.
- Why it looks right
- 5 GHz is faster and less congested.
- Why it's wrong
- Higher frequencies attenuate more through walls and distance; at the edge of coverage 2.4 GHz or an extra access point is better.
Clue to watch for Distance, walls or floors between client and access point.
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Static IP inside the DHCP pool
- What candidates pick
- Give the printer a static address from the middle of the DHCP range.
- Why it looks right
- It makes the address fixed immediately.
- Why it's wrong
- DHCP may lease that address to another device and cause a conflict; use a reservation or exclude the address from the scope.
Clue to watch for Intermittent duplicate address warnings or a printer that disappears.
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Unmanaged switch for segmentation
- What candidates pick
- An inexpensive unmanaged switch to separate guest and staff traffic.
- Why it looks right
- It adds ports cheaply.
- Why it's wrong
- Unmanaged switches cannot create VLANs; segmentation needs a managed switch or separate physical networks.
Clue to watch for The words separate, isolate or VLAN in the requirement.
Answer framework
For any A+ networking scenario, work from the layer the symptom points to.
- Read the client's IP address, mask and gateway first, because APIPA, a wrong subnet or a missing gateway each point to a different fault.
- Identify the service involved and its port and transport, then check whether a firewall rule or wrong port explains the failure.
- For wireless issues, compare band, channel, standard and distance before changing hardware.
- Choose devices by role: switch for local ports, managed switch for VLANs, router between networks, PoE where no outlet exists.
- Prefer the secure, standard option the scenario allows, such as SSH over Telnet, HTTPS over HTTP and reservations over ad hoc static addresses.
Practice question
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Study strategy
Begin with objective 2.1 and drill the port table until recall is instant, grouping ports by job rather than memorizing a flat list. Then study 2.6 and 2.4 together: private ranges, APIPA, masks and gateways, followed by DHCP scopes and DNS record types. These are the concepts most often turned into scenario clues.
Give 2.2 its own session with a frequency and standards table, and include channel overlap and channel width; candidates often underestimate how many questions hinge on 2.4 versus 5 versus 6 GHz behavior. Objectives 2.3, 2.5 and 2.7 reward a one-line definition for each device, service and connection type, so build flash cards that state the job and the distinguishing feature.
Treat 2.8 as a hands-on topic: watch or perform a cable termination and a toner trace so the tools stick. Afterwards, move to Core 1 objective 5.5 (troubleshoot network issues), which applies this material to symptoms, then to Core 2 objectives 1.7 and 2.10 on Windows networking and SOHO security. Finish with timed port and addressing drills until you can answer them without hesitation.
FAQ
How much of A+ Core 1 is Networking?
Networking is 23% of Core 1 (220-1201), second only to Hardware and Network Troubleshooting at 28%. It is not a Core 2 domain, though Core 2 uses it heavily in Windows networking and security objectives.
Which ports must I memorize for A+?
All of those named in objective 2.1: 20/21, 22, 23, 25, 53, 67/68, 80, 110, 137-139, 143, 389, 443, 445 and 3389. Learn the service, purpose and transport for each.
What does a 169.254.x.x address mean?
It is an APIPA address, which Windows assigns when it asks for DHCP and gets no reply. The link works, so look at the DHCP server, scope exhaustion, relay or VLAN placement.
Is 6 GHz Wi-Fi on the A+ exam?
Yes. The V15 objectives list 2.4, 5 and 6 GHz. Know that 6 GHz requires Wi-Fi 6E or later and trades range for clean spectrum and speed.
Do I need subnetting for A+?
Not full subnet calculation. You should recognize common masks, know that the gateway must be on the client's subnet, and identify private, public and APIPA addresses.
What is the difference between a proxy server and a load balancer?
A proxy makes requests on behalf of internal clients and can filter or cache content. A load balancer sits in front of servers and spreads incoming requests across them for performance and availability.
How does this domain relate to troubleshooting?
Core 1 objective 5.5 tests network symptoms such as limited connectivity, high latency, jitter and port flapping, and every diagnosis relies on the addressing, wireless and device knowledge from this domain.
Other IT Fundamentals & Hardware certifications
Where the same subject shows up in other exams. Cards marked "Same subject" open the matching domain.
Test your Domain 2 knowledge
You have covered ports and protocols, Wi-Fi bands, DNS and DHCP, SOHO addressing, network hardware and tools. Check whether you can read the addressing and port clues quickly under timed conditions.
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