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AP Networking · Unit 1 of 5
Network Foundations
Pilot course — no published weighting yet3 lessons · 54 min40 terms
What this unit covers
The topics below follow the published Networking course framework for Unit 1. Networking publishes no per-unit weighting, so there is no percentage to chase here.
Network modelsDevicesAddressingTraffic flow
Lessons in this unit
- Network Models and Encapsulation18 min · 3 objectivesExplain layered network communication · Apply the idea to evidence from a realistic technology scenario · Justify a decision using security, reliability, cost, and user impact
- Addresses, Subnets, and Default Gateways18 min · 3 objectivesExplain IPv4 addressing and subnet boundaries · Apply the idea to evidence from a realistic technology scenario · Justify a decision using security, reliability, cost, and user impact
- Ethernet, Wi-Fi, and Performance18 min · 3 objectivesExplain local media, switching, and performance measures · Apply the idea to evidence from a realistic technology scenario · Justify a decision using security, reliability, cost, and user impact
Every term in Unit 1
All 40 terms we publish for Network Foundations, with definitions. Reading them through is the fastest way to find the ones you cannot define — then drill those in cram mode until you can produce them without the prompt.
- Encapsulation
- Each layer adds its own header to the payload from the layer above: transport header, then IP header, then link frame. The receiver strips them in reverse.
- Broadcast domain
- The set of devices a broadcast reaches. Bounded by routers, and by VLANs on a switch. Oversized broadcast domains waste bandwidth on every host.
- TCP three-way handshake
- SYN → SYN-ACK → ACK. Synchronizes initial sequence numbers in both directions and confirms both hosts are willing before data flows.
- Default gateway
- The router address a host sends traffic to when the destination is not on its own subnet. Wrong or missing gateway is the classic "local works, internet does not" fault.
- Subnet mask
- Marks which bits of an address are network and which are host. Tells a host whether a destination is local or must go via the gateway.
- Computer network
- Two or more devices connected so they can exchange data. Everything else in the course is about how that exchange is organized and protected.
- Protocol
- An agreed set of rules for communication. Devices from different manufacturers interoperate only because the rules are public and shared.
- OSI model
- A seven-layer reference model: Physical, Data Link, Network, Transport, Session, Presentation, Application. A teaching and troubleshooting framework rather than a description of real software.
- Layer 1 — Physical
- Bits on the wire, radio or fiber: cables, connectors, voltages, signaling. Faults here are cut cables and bad ports.
- Layer 2 — Data Link
- Frames on the local segment, addressed by MAC. Switches operate here, and so do VLANs.
- Layer 3 — Network
- Packets between networks, addressed by IP. Routers operate here, and this is the layer that makes the internet possible.
- Layer 4 — Transport
- End-to-end delivery between processes, using TCP or UDP and identified by port number.
- Layers 5–7 — Session, Presentation, Application
- Session establishment, formatting and encryption, and the protocols users meet — HTTP, DNS, SMTP. In practice most software treats these as one.
- TCP/IP model
- The four-layer model actually implemented: Link, Internet, Transport, Application. It maps onto OSI with the top three OSI layers collapsed into one.
- Protocol data unit names
- Data at the application layers, segment at Transport, packet at Network, frame at Data Link, bits at Physical. Naming the PDU names the layer.
- TCP
- Connection-oriented and reliable: a three-way handshake, sequence numbers, acknowledgements and retransmission. Used where every byte must arrive — web, email, file transfer.
- UDP
- Connectionless and unreliable, with no handshake and no retransmission. Lower overhead and latency, used for DNS, streaming, voice and games where a late packet is worse than a lost one.
- Choosing TCP or UDP
- Ask whether a missing piece must be recovered. If a retransmission arrives too late to be useful, UDP is the right answer.
- MAC address
- A 48-bit hardware address, written as twelve hexadecimal digits, burned into a network interface. Used only within a local segment and rewritten at every router hop.
- IPv4 address
- 32 bits, written as four decimal octets from 0 to 255. About 4.3 billion possible addresses, which ran out — hence NAT and IPv6.
- IPv6 address
- 128 bits, written as eight groups of four hexadecimal digits. The address space is large enough that exhaustion is not a concern.
- CIDR notation
- A slash and the number of network bits: 192.168.1.0/24. Replaced the old fixed classes with arbitrary boundaries.
- Network and broadcast addresses
- In a subnet, the all-zeros host portion is the network address and the all-ones is the broadcast. Neither is assignable to a host, which is why a /24 holds 254 usable addresses, not 256.
- Private IP ranges
- 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Not routable on the public internet, which is why NAT is needed to reach it.
- Loopback address
- 127.0.0.1 (::1 in IPv6). Refers to the device itself — pinging it tests the local TCP/IP stack and nothing beyond it.
- APIPA / link-local
- 169.254.x.x, self-assigned when a host wants DHCP and gets no reply. Seeing it is a diagnosis: the DHCP server was unreachable.
- Static vs dynamic addressing
- Static addresses are configured by hand and suit servers, printers and infrastructure. Dynamic addresses come from DHCP and suit everything else.
- Unicast, broadcast, multicast, anycast
- One-to-one, one-to-all-on-the-segment, one-to-a-subscribed-group, and one-to-the-nearest-of-many. Broadcasts do not cross a router.
- Collision domain
- The set of devices whose transmissions can collide. A hub is one shared collision domain; every switch port is its own, which is why switches replaced hubs.
- Hub
- A layer 1 device repeating every frame out of every port. Obsolete, and useful in this course as the contrast that explains what a switch does.
- Switch
- A layer 2 device forwarding frames only to the port where the destination MAC lives, learned from traffic it has seen.
- Router
- A layer 3 device forwarding packets between different networks using IP addresses and a routing table. Blocks broadcasts by design.
- Access point
- Bridges wireless clients onto a wired network. A layer 2 device, and not a router even though home equipment usually combines the two.
- Modem
- Converts between the signaling of a provider medium and Ethernet. Not a router, and not a firewall.
- Load balancer
- Distributes incoming connections across several servers for capacity and availability. Also hides how many servers there actually are.
- Bandwidth vs throughput vs latency
- Bandwidth is theoretical capacity, throughput is what you actually achieve, and latency is delay before data starts arriving. A high-bandwidth satellite link still feels slow.
- Jitter
- Variation in latency between packets. Barely matters for a file transfer and is the main quality problem for voice and video.
- Full vs half duplex
- Full duplex sends and receives simultaneously; half duplex alternates. A duplex mismatch produces a link that works badly rather than not at all — the hardest kind of fault to spot.
- Twisted pair, fiber, wireless
- Copper is cheap and distance-limited; fiber carries more, further, and is immune to electromagnetic interference; wireless trades throughput and predictability for mobility.
- LAN, WAN, MAN, PAN
- Local, wide, metropolitan and personal area networks — categories by geographic scope rather than by technology.
What examiners penalize here
- For a scenario about **layered network communication**, identify the decisive evidence before naming a response. A defensible conclusion here is: The application data remains conceptually the same while lower-layer framing changes from link to link.
- For a scenario about **IPv4 addressing and subnet boundaries**, identify the decisive evidence before naming a response. A defensible conclusion here is: A router must move the packet between the two /24 networks.
- For a scenario about **local media, switching, and performance measures**, identify the decisive evidence before naming a response. A defensible conclusion here is: The evidence points to wireless quality, not insufficient advertised internet bandwidth.
Practice Networking
Our practice bank is drawn from across the whole course rather than filtered to one unit, which is closer to how the exam asks anyway — it will not tell you which unit a question is testing.
Questions about this unit
How much of the AP Networking exam is Unit 1?
The Networking course framework does not publish a per-unit weighting, so there is no percentage to quote for Unit 1 and anyone who gives you one is guessing. Spread your time by where your own errors are instead.
What topics are covered in Networking Unit 1?
Network Foundations covers Network models, Devices, Addressing and Traffic flow. We publish 40 terms with definitions for this unit, all of them on this page.
How should I study Networking Unit 1?
Read the 3 lessons below first — about 55 minutes — then drill the 40 terms in cram mode until you can produce each definition from memory rather than just recognize it. Recognition is what makes a unit feel finished when it is not. Finish with practice questions and read the explanation for every one you get right by elimination as well as the ones you miss.
All 5 units of AP Networking
Unit names, topics and exam weights follow the published College Board course framework for AP Networking. AP® is a trademark registered by the College Board, which does not endorse this site.