Networking Fundamentals
The OSI model, subnetting, TCP versus UDP, DNS and firewalls explained from first principles — the network fundamentals every DevOps and backend engineer is expected to know, remembered with spaced repetition.
- flashcards
- 69
- flashcards
- per day
- ~10 min
- per day
- level
- Beginner → Intermediate
- level
- modules
- 6
- modules
Why learn networking fundamentals?
Every deploy, API call and container you ship rides on the same handful of networking concepts — the OSI model, IP addressing, ports, DNS and firewalls. Yet these are exactly the topics developers skip, then re-learn under pressure when a service cannot reach its database or a request mysteriously times out.
This track builds the mental model layer by layer: how data is encapsulated as it moves down the stack, how CIDR and subnet masks split a network, why TCP is reliable and UDP is fast, how a DNS name becomes an IP address, and how switches, routers and firewalls actually move and filter packets.
It stays vendor-neutral and conceptual — the theory that outlasts any single tool or cloud. Spaced repetition turns "I think it is a /24…" into subnetting you can do in your head. For the command-line side (dig, ss, tcpdump) and the application layer, see the Linux and HTTP tracks.
6 modules, seed to bloom
Each module is a set of flashcards — 69 in total. Answer, review, and watch your knowledge grow from seed to full bloom.
Network Models
OSI and TCP/IP layered models
9 cardsIP Addressing & Subnetting
IPv4/IPv6, CIDR, subnets, and NAT
13 cardsTransport & Ports
TCP vs UDP, the handshake, ports and sockets
13 cardsDNS
Name resolution, record types, and DNSSEC
12 cardsRouting & Switching
Switches, routers, MAC/ARP, and routing tables
11 cardsFirewalls, Security Groups & Load Balancing
Firewalls, cloud security groups, and load balancing
11 cardsSample questions
A taste of the real flashcards. Pick an answer, then reveal the explanation.
What are the seven OSI model layers in order from Layer 1 to Layer 7?
- APhysical, Data Link, Network, Transport, Session, Presentation, Application
- BPhysical, Data Link, Transport, Network, Session, Presentation, Application
- CPhysical, Network, Data Link, Transport, Session, Presentation, Application
- DPhysical, Data Link, Network, Transport, Presentation, Session, Application
How many usable host addresses does a /24 (255.255.255.0) subnet provide?
- A254 — the 256 addresses in the block minus the network and broadcast addresses
- B256 — every address in the block can be freely assigned to a host on the subnet
- C255 — every address in the block except the single reserved network address itself
- D253 — the block minus the network, the broadcast, and the reserved gateway address
What is the key difference between TCP and UDP?
- ATCP is connection-oriented and reliable; UDP is connectionless and best-effort
- BTCP is connectionless and best-effort; UDP is connection-oriented and reliable
- CTCP is encrypted end-to-end; UDP is unencrypted and therefore always faster
- DTCP works only on local networks; UDP works only across the public internet
What does DNSSEC add to the DNS?
- ACryptographic signatures that let resolvers verify a record's authenticity
- BTransport encryption that hides every DNS query from network eavesdroppers
- CLoad balancing that spreads DNS queries across many redundant resolvers
- DAutomatic caching that stores popular records closer to the requesting client
Learn it once, keep it for good
Answer a question
Each card is one practical concept with multiple options. Pick what you think is right.
Get the full answer
See the correct option plus a clear explanation, and a link to deeper docs when one is available.
Review at the right time
A spaced-repetition engine (SM-2 or FSRS) resurfaces each card just before you would forget it.
Why networking is worth your time
The base layer of everything
Containers, clouds, CI/CD and microservices all sit on networking. It pays off in every other track.
Debug connectivity fast
Reading subnets, ports, DNS records and firewall rules correctly turns "it cannot connect" into a quick fix.
Vendor-neutral and durable
OSI, TCP/IP and subnetting do not change with the tool of the month — learn them once, use them for good.
Interview-ready
OSI layers, TCP vs UDP, subnetting and DNS are staples of DevOps, SRE and backend interviews.
Common questions
How is this different from the HTTP & Networking track? +
This track covers the lower layers — the OSI and TCP/IP models, IP addressing, ports, DNS, routing and firewalls. The HTTP & Networking track focuses on the application layer: HTTP methods, status codes, caching and TLS.
Do I need any prior networking knowledge? +
No. It starts from the OSI model and IP addressing and builds up, so beginners can start from zero while experienced engineers fill the gaps.
Is it free? +
Yes, completely free. No registration or credit card is required, and all your progress is stored locally in your browser.
Does it cover subnetting and CIDR? +
Yes. A full module covers IP addressing, subnet masks, CIDR notation, usable host counts, private ranges and NAT.
Ready to master networking?
Plant your first seed today. Ten minutes a day is all it takes to understand the network from the wire up.