Core 1 Domain 2: Networking (23%)¶

Overview¶

Networking is almost a quarter of Core 1. It is the A+ slice of what Network+ covers in depth: ports and protocols, Wi-Fi, the services networked hosts provide, DNS and DHCP configuration, the hardware in a small office, IP addressing, internet connection types, and the tools you carry to fix cabling. Expect at least one PBQ that asks you to match ports to protocols or configure a SOHO router.

The objectives are:

• 2.1 Compare and contrast TCP and UDP ports, protocols, and their purposes.
• 2.2 Explain wireless networking technologies.
• 2.3 Summarize services provided by networked hosts.
• 2.4 Explain common network configuration concepts.
• 2.5 Compare and contrast common networking hardware devices.
• 2.6 Given a scenario, configure basic wired/wireless SOHO networks.
• 2.7 Compare and contrast internet connection types, network types, and their characteristics.
• 2.8 Explain networking tools and their purposes.

2.1 Ports, Protocols, TCP and UDP¶

TCP vs UDP¶

A useful memory hook: TCP is a phone call where both sides confirm they heard each other. UDP is shouting across a room and hoping.

The port list¶

These fourteen entries are named in the objective. Learn them in both directions: port to protocol and protocol to port.

POP3 vs IMAP is a favorite question. POP3 downloads and usually deletes from the server, so mail lives on one device. IMAP leaves mail on the server and keeps every device in sync.

📖 IANA Service Name and Port Number Registry - The official registry for well-known ports

2.2 Wireless Networking Technologies¶

Frequencies and channels¶

• Regulations - Each country's regulator decides which channels and power levels are legal. That is why a router has a country setting.
• Channel selection - Pick channels that do not overlap with neighbors. A Wi-Fi analyzer shows what is in use.
• Channel width - 20, 40, 80, 160 MHz, and 320 MHz on Wi-Fi 7. Wider channels are faster but more likely to overlap. On a crowded 2.4 GHz band, stick to 20 MHz.

802.11 standards¶

Real throughput is far lower than the theoretical figure. The whole cell shares the airtime, and the slowest client drags everyone down on older standards.

📖 IEEE 802.11 Working Group - The body that publishes the 802.11 standards

Other wireless technologies¶

• Bluetooth - Short-range personal area network. Low Energy (BLE) variants power fitness trackers and beacons.
• NFC - A few centimeters. Contactless payment, badge readers, quick pairing.
• RFID - Radio tags read at a distance. Inventory, toll tags, access badges. Passive tags have no battery and are powered by the reader.

2.3 Services Provided by Networked Hosts¶

Server roles¶

Internet appliances¶

Legacy, embedded, and IoT¶

• SCADA - Supervisory control and data acquisition. Controls industrial processes such as power grids, water treatment, and factories. Often old, hard to patch, and should be isolated on its own network.
• IoT devices - Smart thermostats, cameras, speakers, sensors. Weak default passwords and rare updates. Put them on a separate VLAN or guest network.

2.4 Network Configuration Concepts¶

DNS record types¶

Email authentication (spam management)¶

These three live in TXT records and work together:

flowchart LR
    M["Incoming email"] --> S{"SPF: sending server<br/>listed for domain?"}
    M --> D{"DKIM: signature<br/>valid?"}
    S --> P["DMARC policy<br/>checks alignment"]
    D --> P
    P -->|Pass| I["Deliver to inbox"]
    P -->|Fail, p=quarantine| Q["Spam folder"]
    P -->|Fail, p=reject| R["Reject message"]

How a receiving mail server combines SPF and DKIM results under the sender's DMARC policy.

📖 DMARC.org Overview - How DMARC builds on SPF and DKIM

DHCP concepts¶

The DHCP conversation is DORA: Discover, Offer, Request, Acknowledge. A client that gets no answer assigns itself an APIPA address.

VLAN and VPN¶

• VLAN - Splits one physical switch into several logical networks. Keeps guest, IoT, voice, and staff traffic apart. Traffic between VLANs must pass through a router or Layer 3 switch.
• VPN - An encrypted tunnel across an untrusted network. Site-to-site VPNs join offices. Client VPNs let remote workers reach internal resources.

2.5 Networking Hardware¶

Power over Ethernet¶

PoE sends power and data over the same Ethernet cable. It powers access points, VoIP phones, and cameras without a nearby outlet.

• PoE switch - Powers devices directly from its ports. Check the total power budget.
• PoE injector - Adds power to one cable when the switch does not support PoE.

2.6 Configuring SOHO Networks¶

IPv4 addressing¶

• Private addresses are not routable on the internet. The SOHO router uses NAT to share one public address among all internal devices.
• APIPA - A Windows client that cannot reach DHCP gives itself a 169.254.x.x address. It can talk to other APIPA hosts on the same segment, but not to the internet. Seeing APIPA almost always means a DHCP problem.
• Static addressing suits servers, printers, and network gear. Dynamic (DHCP) suits everything else.
• Subnet mask - Separates the network part from the host part. 255.255.255.0 (/24) is the SOHO default: 254 usable hosts.
• Default gateway - The router address. Without it, a host can reach only its own subnet.

IPv6 basics¶

• 128-bit addresses written as eight groups of four hex digits. Leading zeros can be dropped and one run of all-zero groups can be written ::.
• ::1 is loopback. Addresses starting fe80:: are link-local, always present on an IPv6 interface.
• IPv6 hosts can configure themselves with SLAAC, or use DHCPv6.

SOHO configuration checklist¶

flowchart TB
    A["Connect modem/ONT to router WAN port"] --> B["Log in and change the default admin password"]
    B --> C["Update firmware"]
    C --> D["Set LAN subnet and DHCP scope,<br/>add reservations for printers"]
    D --> E["Configure Wi-Fi: SSID, WPA3 or WPA2-AES,<br/>strong passphrase, guest network"]
    E --> F["Firewall: disable UPnP if not needed,<br/>forward only required ports"]
    F --> G["Test wired and wireless clients"]

A typical order of work when setting up a small office router. The security settings are covered again in 07 - Security.

2.7 Internet Connection Types and Network Types¶

Internet connection types¶

Network types¶

2.8 Networking Tools¶

Exam Tips and Traps¶

1. APIPA (169.254.x.x) means DHCP failed. Check the DHCP server, the cable, and the switch port.
2. POP3 downloads; IMAP syncs. Users with mail on several devices need IMAP (or Exchange).
3. Telnet 23 and FTP 20/21 are cleartext. The secure answer is SSH 22 or SFTP.
4. 2.4 GHz non-overlapping channels are 1, 6, 11.
5. 6 GHz means Wi-Fi 6E or Wi-Fi 7, and WPA3.
6. DHCP reservation keeps a printer on the same IP without configuring it statically.
7. MX points to mail servers; TXT holds SPF, DKIM, DMARC.
8. Toner probe traces a cable; cable tester verifies it.
9. Unmanaged switch has no VLANs. VLANs require a managed switch.
10. ONT is fiber, cable modem is coax, DSL is phone line.

Related Notes¶

• 05 - Hardware and Network Troubleshooting - Network symptoms and fixes
• 06 - Operating Systems - ipconfig, ping, tracert, nslookup, netstat
• Network+ (N10-009) - The deeper networking cert that follows A+
• Fact Sheet - Port table for last-minute review