Exam prep · Free college course
A complete introductory computer networking course, organized around the chapters of Computer Networks: A Systems Approach and checked against the RFCs and IANA registries. It starts with network types, the OSI and TCP/IP layering models, encapsulation and bandwidth-delay, then the physical and data link layers: framing, error detection, sliding windows and 802.11. Ethernet, switch learning, spanning tree, VLANs and ARP lead into IPv4 headers, private ranges, CIDR, subnet calculations, NAT, DHCP and ICMP, then IPv6 addressing. Routing covers longest-prefix match, RIP, OSPF, BGP and administrative distance. The transport units cover ports, UDP, the TCP header and flags, the handshake and state machine, flow control, retransmission, slow start and AIMD. The course closes with HTTP, email, FTP and SSH, well-known ports, DNS records and resolution, TLS, IPsec and firewalls, and the command-line tools and troubleshooting method you use to find a fault. Subnet and window calculations are typed cards whose answers were recomputed by script. Cards are text only, so every packet diagram is described in words or as a small table.
Copied straight from the course. In the app, each wrong option also gets its own explanation.
Card 1Splitting 192.168.1.0/24 into /27 subnets gives how many subnets?
8. Each /27 is 32 addresses, so a /24 splits into 256 / 32 = 8 subnets.
Card 2If the final ACK of the handshake is lost, what happens?
It still works; the server reaches ESTABLISHED on the first data segment.. Every segment carries the next-expected sequence number, so the data segment also completes the handshake.
Card 3A tcpdump capture shows a SYN going out and a RST coming back. What does that tell you?
The port is closed. A RST in reply to a SYN means the host is up and nothing listens on that port.
Encodr is a friendly, game-like flashcard app. Spaced repetition schedules every review for you, and the rest keeps you coming back.
Study a little each day to build a streak. A streak freeze forgives a missed day.
Small goals each day, like finishing a set, with a little celebration when you clear one.
Sessions come in bite-size sets of 15 to 25 answers, so there is always a natural place to stop.
Earn XP and level up, then see friends on a daily leaderboard and send them a nudge.
Yes. Create a free Encodr account and all 12 units and 1,201 cards are yours to study, with spaced repetition scheduling your reviews.
The chapters of Computer Networks: A Systems Approach (Peterson and Davie, CC BY 4.0), the IETF RFCs, and the IANA port and protocol registries. The cards are rewritten, not copied, and each one lists its source.
Network models and encapsulation, Ethernet and switching, IPv4 and IPv6 addressing, subnetting, routing protocols, UDP and TCP, congestion control, application protocols and ports, DNS, network security basics, and command-line troubleshooting.
Yes. Subnet masks, CIDR, host and subnet counts, and window and delay calculations are practice cards, and every answer was recomputed by script.
No. It is text only: there are no labs, no packet captures and no simulator, so you will not configure a router or read a live trace here. Port numbers, header fields and flag bits are memorization-heavy, which is where spaced repetition helps most; pair the course with real practice for the hands-on skills.
The course draws on the Systems Approach text under CC BY 4.0, plus RFCs and IANA registries, which are public references. The cards themselves are Encodr study material for your own learning.