Computer Networks
Layers, TCP/IP, routing, and the path a packet takes from socket to wire.
Topics in this field: 71
- What is Networking? — Independent machines exchanging messages over a shared, unreliable medium.
- LAN — A local area network: one broadcast domain or a few, under one administration.
- WAN — A wide-area network spanning sites and usually several providers.
- MAN — A metropolitan network: a city-scale fabric, often provider-owned fiber.
- PAN — A personal area network: Bluetooth, USB, the devices around one person.
- Network Topology — Bus, star, ring, mesh, hybrid — how nodes are wired, logically and physically.
- Client/Server — A role split: clients initiate, servers wait and respond. Most of the internet.
- Peer-to-Peer — Nodes that are both client and server. BitTorrent, some overlay networks, some blockchains.
- Network Devices — The box-level view: hubs, switches, routers, firewalls, and where each sits in the stack.
- Hub — A physical-layer repeater: every bit out every port. Collision domain = the whole hub.
- Switch — A data-link device that forwards frames by MAC and splits collision domains.
- Router — A network-layer device that forwards packets between subnets using a routing table.
- Bridge — Connects two L2 segments and learns MACs. A switch is a multi-port bridge.
- Gateway — A node that translates between networks or protocols — often just 'the router'.
- Repeater — Amplifies or retimes a signal to extend a physical segment.
- Modem — Modulator-demodulator: analog carrier on, bits off, and the reverse.
- Access Point — A bridge between wireless stations and a wired LAN, with association and encryption.
- Firewall — A policy box: filter, NAT, or proxy traffic by rule. Host or network, stateful or not.
- OSI Model — Seven layers of function, from photons to application messages. The shared language of networking.
- Layer 7 — Application — The OSI layer where applications meet the network: HTTP, DNS, SMTP, and their data.
- Layer 6 — Presentation — Syntax and encryption: encoding, compression, TLS as it is often taught at this layer.
- Layer 5 — Session — Dialogs: setup, teardown, and checkpoints. Thin in TCP/IP, explicit in some RPC systems.
- Layer 4 — Transport — Process-to-process: ports, reliability, and congestion control. TCP and UDP live here.
- Layer 3 — Network — Host-to-host across hops: IP, routing, ICMP. Packets and logical addresses.
- Layer 2 — Data Link — Hop-to-hop frames: MAC addresses, Ethernet, switches, and error detection.
- Layer 1 — Physical — Bits on a medium: voltage, light, radio, connectors, and the limits of Shannon.
- TCP/IP Model — Four layers the internet actually runs: application, transport, internet, network access.
- OSI vs TCP/IP — A seven-layer teaching model versus a four-layer running model. Same ideas, different cuts.
- Signals — The physical representation of bits: analog vs digital, encoding, and noise.
- Bandwidth — How much spectrum or bit-rate a channel offers. Not the same thing as throughput.
- Latency — One-way or round-trip delay. Propagation, transmission, queueing, processing.
- Transmission Media — Copper, fiber, and wireless — each with a noise, cost, and distance story.
- Fiber — Light in glass. Huge bandwidth, long reach, immunity to electrical noise.
- Copper — Twisted pair and coax. Cheap, familiar, and still how most desks are wired.
- Wireless — Shared spectrum, fading, and a MAC that is nothing like a wire.
- Modulation — Imprinting bits on a carrier: AM, FM, PSK, QAM — the physical alphabet.
- Frames — The data-link PDU: header, payload, trailer. Ethernet's 14-byte header is the one you will draw.
- MAC Addresses — 48-bit link-layer identifiers. Unique-ish, local or universal, unicast or group.
- Ethernet — The LAN technology: CSMA/CD history, switching present, 802.3 framing.
- Switching — Learn MACs, flood unknowns, forward knowns, filter the rest. CAM tables and STP.
- ARP — Resolve IPv4 to MAC on a LAN. The cache, the timeout, and the spoof.
- Error Detection — Parity, checksums, CRC. Detecting corruption is cheaper than preventing it.
- VLANs — One physical switch, many broadcast domains. 802.1Q tags and trunk ports.
- IP — The internet's network protocol: best-effort datagrams and hierarchical addresses.
- IPv4 — 32-bit addresses, dotted quad, fragmentation, and a header you should be able to sketch.
- IPv6 — 128-bit addresses, no NAT-as-crutch, SLAAC, and a simpler header.
- Subnetting — Carving a prefix into smaller networks. Masks, hosts, and the all-zero/all-one rules.
- CIDR — Classless addressing: a prefix and a length. Aggregation is the point.
- Routing — Choosing a next hop. Tables, longest prefix match, and intra- vs inter-domain.
- ICMP — IP's control plane for errors and diagnostics. Ping and traceroute ride it.
- NAT — Rewriting addresses (and usually ports) so many hosts share a public IP.
- Routing Protocols — RIP, OSPF, BGP: how routers learn paths they did not configure by hand.
- TCP — Reliable, ordered, congestion-controlled byte streams between two ports.
- UDP — Datagrams with ports and a checksum. No connection, no retransmission, no congestion control.
- Ports — 16-bit transport addresses that multiplex a host. Well-known, registered, ephemeral.
- TCP Handshake — SYN, SYN-ACK, ACK. Sequence numbers exchanged so a connection can start.
- TCP Teardown — Four-way (or three-way with FIN-ACK) close, TIME-WAIT, and why half-open exists.
- Flow Control — Stopping a fast sender from drowning a slow receiver. TCP's window.
- Congestion Control — Protecting the network from collapse: slow start, AIMD, ECN, and BBR.
- DNS — The hierarchical lookup that turns names into records — usually addresses.
- DHCP — Automatic host configuration: address, mask, gateway, DNS, lease.
- HTTP — The application protocol of the web: methods, status codes, headers, and now HTTP/2 and /3.
- HTTPS — HTTP over TLS. Confidentiality, integrity, and (usually) server authentication.
- FTP — A historic file protocol with separate control and data channels. Prefer SFTP/HTTPS.
- SMTP — How mail moves between MTAs. Store-and-forward, MX records, and spam as an adversarial load.
- SSH — Authenticated, encrypted remote shells and tunnels. Keys, not passwords, if you can.
- WebSockets — A TCP-backed, full-duplex channel started with an HTTP upgrade.
- Wi-Fi — 802.11: association, airtime, and a MAC that is nothing like a switched Ethernet.
- BGP — The internet's inter-domain routing protocol: path vectors, policy, and the default-free zone.
- OSPF — A link-state IGP: flood LSAs, run Dijkstra, install routes in the RIB.
- Spanning Tree — A loop-free active topology on a switched LAN. Without it, broadcasts amplify until the LAN dies.