Study Hub / CompTIA Network+ (N10-009) / Domain 1.0
CompTIA Network+ (N10-009) Domain 1.0: Networking Concepts — Explained
Domain 1.0 is the language of networking: the models that describe how data moves, the ports and protocols that identify services, and the addressing that gets packets to the right place. Everything else in networking is built on this vocabulary.
1.1 — The OSI model vs. the TCP/IP model
Two models describe the same journey of data from one machine to another. The OSI model has seven layers; the TCP/IP model compresses them into four. Think in OSI and translate to TCP/IP.
- L7 Application — what the user touches: HTTP, DNS, SMTP. (TCP/IP: Application)
- L6 Presentation — data formatting: encryption, compression, encoding. (TCP/IP: Application)
- L5 Session — managing connections between apps. (TCP/IP: Application)
- L4 Transport — end-to-end delivery: TCP vs. UDP, port numbers. (TCP/IP: Transport)
- L3 Network — logical addressing and routing: IP, routers. (TCP/IP: Internet)
- L2 Data Link — physical addressing on the local network: MAC addresses, switches, frames. (TCP/IP: Network Access)
- L1 Physical — the actual bits on the wire: cables, hubs, signaling. (TCP/IP: Network Access)
1.2 — Ports, protocols, and what they do
A port number identifies the service on a machine; the protocol defines the language. Together with an IP address, they form a socket — the full address of a conversation.
- Well-known ports (0–1023) — assigned to standard services: 80 HTTP, 443 HTTPS, 22 SSH, 25 SMTP, 53 DNS, 67/68 DHCP, 389 LDAP, 3389 RDP.
- Registered ports (1024–49151) — assigned to vendor applications on request.
- Dynamic/private ports (49152–65535) — picked at random for the client side of a connection.
TCP vs. UDP is a fundamental transport question: TCP is connection-oriented — three-way handshake, sequencing, acknowledgments, retransmission. Reliable but slower. UDP is connectionless — fire and forget. Faster, no guarantees. Rule of thumb: if the application can't tolerate loss (web, email, file transfer), it's TCP; if it values speed over perfection (streaming, VoIP, DNS queries), it's UDP.
1.3 — IP addressing and subnetting concepts
Every device needs a logical address (IP) to be routable beyond its local network.
- IPv4 — 32-bit dotted decimal (192.168.1.10). About 4.3 billion addresses — exhausted long ago, which is why NAT exists.
- IPv6 — 128-bit hexadecimal (2001:db8::1). Effectively unlimited; no NAT needed, autoconfiguration built in.
- Private ranges (RFC 1918) — 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. Not routable on the internet; reused inside every organization.
- APIPA (169.254.x.x) — the address a host gives itself when DHCP fails. Seeing one means "DHCP is broken," not "the network is fine."
- Subnetting — borrowing host bits to carve one network into smaller ones. A /26 gives 4 subnets of 62 usable hosts each. The block-size method: block size = 256 − interesting octet of the mask.
1.4 — Switching and routing concepts
Switches and routers both move packets, at different layers and different scopes:
- Hub (L1) — repeats everything out every port. One collision domain; obsolete.
- Switch (L2) — learns MAC addresses per port and forwards frames only where they need to go. Each port is its own collision domain; all ports share a broadcast domain.
- Router (L3) — forwards packets between networks using IP addresses and a routing table. Each router interface is its own broadcast domain.
- VLAN — a virtual LAN: one physical switch carved into multiple logical broadcast domains. Devices on different VLANs can't talk without a router (or layer-3 switch).
- Default gateway — the router interface a host sends traffic destined off its network to. No gateway, no internet.
The must-memorize table: essential ports and protocols
If a question names a service, you name the port. Start here.
| Port | Protocol | Used for |
|---|---|---|
| 20/21 | FTP | File transfer (plaintext) |
| 22 | SSH / SFTP | Secure shell; secure file transfer |
| 23 | Telnet | Remote shell (plaintext — legacy) |
| 25 | SMTP | Sending email |
| 53 | DNS | Name resolution |
| 67/68 | DHCP | Automatic IP assignment |
| 80 | HTTP | Web (plaintext) |
| 110 | POP3 | Receiving email (download) |
| 143 | IMAP | Receiving email (server-synced) |
| 443 | HTTPS | Secure web |
| 389 | LDAP | Directory services |
| 3389 | RDP | Windows remote desktop |
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 workstation suddenly has the IP address 169.254.44.12. What does this tell the technician?
- A. A. The workstation is using a valid public IP address
- B. B. DHCP failed, and the host assigned itself an APIPA address
- C. C. The workstation has been assigned a reserved private address
- D. D. IPv6 autoconfiguration has completed successfully
Show answer & reasoning
B. 169.254.0.0/16 is APIPA — the range Windows (and others) self-assign when no DHCP server answers. It means the host has no usable network configuration: no gateway, no DNS. The technician's next step is DHCP troubleshooting, not IP troubleshooting.
2. A video-conferencing application uses UDP instead of TCP for its media streams. Why is that the right choice?
- A. A. UDP encrypts the stream, which TCP cannot do
- B. B. UDP guarantees delivery, which matters most for video
- C. C. UDP's low overhead suits real-time traffic, where a late packet is worse than a lost one
- D. D. TCP cannot carry video data at all
Show answer & reasoning
C. Real-time media would rather drop a late packet than wait for a retransmission — waiting causes stutter. UDP's fire-and-forget model fits perfectly. TCP's reliability mechanisms (A/B get the properties backwards) would add delay. TCP certainly can carry video (D) — it's just the wrong tradeoff for live streams.
3. Two departments share one physical switch but must not see each other's broadcast traffic. What is the simplest solution?
- A. A. Install a router between every workstation
- B. B. Place each department in its own VLAN
- C. C. Assign both departments APIPA addresses
- D. D. Replace the switch with a hub
Show answer & reasoning
B. A VLAN splits one switch into separate logical broadcast domains — exactly the requirement, with no new hardware. A router (A) per workstation is absurd; APIPA (C) breaks connectivity; a hub (D) makes things worse by merging everything into one collision domain.
4. A user can ping the default gateway but cannot reach any website by name — though pinging 8.8.8.8 works. Which layer is the problem at?
- A. A. Layer 1 — the cable is likely damaged
- B. B. Layer 2 — the switch MAC table is full
- C. C. Layer 3 — the routing table is missing a route
- D. D. Layer 7 — DNS resolution is failing
Show answer & reasoning
D. IP connectivity works (8.8.8.8 replies; the gateway replies), so L1–L3 are fine. Only names fail — that's DNS, an Application-layer (L7) service. The giveaway pattern: "IP works, names don't" always means DNS.
This was one domain. The simulator drills all 5.
This free preview covered Networking Concepts (Domain 1.0, 23%). Not covered here: Network Implementation (Domain 2.0, 20%); Network Troubleshooting (Domain 5.0, 24%). The hands-on domains — device configuration and scenario troubleshooting — 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 Network+ Study Guide is in the ByteBar shop on Etsy.
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