Computer Networks workbook: OSI / TCP-IP layers, application / transport / network / link protocols, tools, and real network postmortems.http://localhost:4321/http://localhost:4321/computer-networks/aloha-and-slotted-aloha/http://localhost:4321/computer-networks/aloha-and-slotted-aloha/The original stochastic medium-access protocol from 1971 Hawaii, the throughput math (18% and 37%), and what slotting bought.Sat, 30 May 2026 00:00:00 GMTFoundationalconceptLink Layeralohaslotted-alohamacrandom-accesslink-layerhttp://localhost:4321/computer-networks/application-layer-overview/http://localhost:4321/computer-networks/application-layer-overview/What apps actually do on top of the transport layer — process-to-process messaging, architectures, and the protocols you'll meet.Sat, 30 May 2026 00:00:00 GMTFoundationalconceptApplication Layerapplication-layerhttpdnsprotocolsfundamentalshttp://localhost:4321/computer-networks/brief-history-of-the-internet/http://localhost:4321/computer-networks/brief-history-of-the-internet/ARPANET → NSFNET → commercial Internet. The forty-year arc and the design decisions that ossified into today's stack.Sat, 30 May 2026 00:00:00 GMTFoundationalconceptFoundationshistoryarpanetnsfnettcp-ipfundamentalshttp://localhost:4321/computer-networks/implementing-dijkstra-link-state-project/http://localhost:4321/computer-networks/implementing-dijkstra-link-state-project/From a link-state database to a forwarding table in O((V+E) log V). The algorithm OSPF runs on every router.Sat, 30 May 2026 00:00:00 GMTIntermediatebuilding-blockTools & Practiceprojectpythonroutingospfdijkstralink-statehttp://localhost:4321/computer-networks/implementing-rip-project/http://localhost:4321/computer-networks/implementing-rip-project/Build a small network of router processes that exchange distance vectors, converge to shortest paths, and survive a link failure.Sat, 30 May 2026 00:00:00 GMTIntermediatebuilding-blockTools & Practiceprojectpythonroutingripdistance-vectorhttp://localhost:4321/computer-networks/internet-standards-and-rfcs/http://localhost:4321/computer-networks/internet-standards-and-rfcs/Who actually governs the Internet? The bodies, the RFC process, the registries — how a protocol becomes interoperable.Sat, 30 May 2026 00:00:00 GMTFoundationalconceptFoundationsstandardsrfcietfianaicannhttp://localhost:4321/computer-networks/life-of-a-packet/http://localhost:4321/computer-networks/life-of-a-packet/A single HTTP request from address-bar keypress to rendered page — ARP, DHCP, DNS, IP, TCP, HTTP and back, narrated layer by layer.Sat, 30 May 2026 00:00:00 GMTIntermediatesystemNetwork Layerend-to-endlayershttptcpdnshttp://localhost:4321/computer-networks/network-layer-overview/http://localhost:4321/computer-networks/network-layer-overview/Forwarding vs routing, the control plane vs the data plane — what turns 'a wire between two hosts' into 'the Internet'.Sat, 30 May 2026 00:00:00 GMTFoundationalconceptNetwork Layernetwork-layeripforwardingroutingfundamentalshttp://localhost:4321/computer-networks/simulating-spanning-tree-project/http://localhost:4321/computer-networks/simulating-spanning-tree-project/A loop-free spanning tree over a switched-LAN graph: root election, port roles, BPDU exchange, the convergence walk.Sat, 30 May 2026 00:00:00 GMTIntermediatebuilding-blockTools & Practiceprojectpythonstpswitchingspanning-treehttp://localhost:4321/computer-networks/static-mac-allocation-tdma-fdma-cdma/http://localhost:4321/computer-networks/static-mac-allocation-tdma-fdma-cdma/Pre-allocated time, frequency, or code slots. The schemes mobile and satellite links rely on, and why static beats stochastic for them.Sat, 30 May 2026 00:00:00 GMTIntermediateconceptLink Layermactdmafdmacdmachannel-partitioninghttp://localhost:4321/computer-networks/static-vs-dynamic-routing/http://localhost:4321/computer-networks/static-vs-dynamic-routing/Hand-edited tables vs protocols that converge. When each is correct, and the operational cost of choosing wrong.Sat, 30 May 2026 00:00:00 GMTIntermediateconceptNetwork Layerroutingstatic-routingdynamic-routingospfbgphttp://localhost:4321/computer-networks/udp-chat-app-project/http://localhost:4321/computer-networks/udp-chat-app-project/A small but realistic project: many clients, one relay server, broadcast over UDP. The framing, the keep-alive, the cleanup.Sat, 30 May 2026 00:00:00 GMTFoundationalbuilding-blockTools & Practiceprojectpythonudpsocketschathttp://localhost:4321/computer-networks/access-networks/http://localhost:4321/computer-networks/access-networks/How end hosts get on the Internet — the last-mile technologies, their bandwidth shapes, and where they're going.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptFoundationsaccess-networklast-miledslcablefibercellularhttp://localhost:4321/computer-networks/bittorrent/http://localhost:4321/computer-networks/bittorrent/Tracker + swarm + pieces + tit-for-tat. The protocol that made P2P scale and still teaches the patterns.Sun, 24 May 2026 00:00:00 GMTIntermediatesystemApplication Layerbittorrentp2pswarmtit-for-tathttp://localhost:4321/computer-networks/client-server-vs-p2p/http://localhost:4321/computer-networks/client-server-vs-p2p/Two app-layer architectures, their scaling shapes, and the hybrid (BitTorrent + trackers) that combines them.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptApplication Layerclient-serverp2parchitecturescalinghttp://localhost:4321/computer-networks/arp/http://localhost:4321/computer-networks/arp/Mapping IPv4 addresses to MAC addresses inside a subnet. The cache, the request/reply, and the spoofing risk.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockNetwork Layerarpnetwork-layerlayer-2securityhttp://localhost:4321/computer-networks/aws-us-east-1-2017-s3-outage/http://localhost:4321/computer-networks/aws-us-east-1-2017-s3-outage/A misconfigured command in the S3 billing system; cascading failure through us-east-1; the lessons on blast radius.Sun, 24 May 2026 00:00:00 GMTFoundationalpostmortemSystems & Postmortemsawss3us-east-1cascading-failureblast-radiushttp://localhost:4321/computer-networks/cookies-and-sessions/http://localhost:4321/computer-networks/cookies-and-sessions/Stateful sessions over a stateless protocol, Set-Cookie / Cookie headers, SameSite, Secure, HttpOnly, and the alternatives.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockApplication Layercookiessessionshttpweb-securityhttp://localhost:4321/computer-networks/cloudflare-2019-regex-outage/http://localhost:4321/computer-networks/cloudflare-2019-regex-outage/A bad WAF regex with exponential backtracking; 30 minutes of global edge downtime; the postmortem on safe deploys.Sun, 24 May 2026 00:00:00 GMTFoundationalpostmortemSystems & Postmortemscloudflarewafregexedgeglobal-outagehttp://localhost:4321/computer-networks/data-link-layer-overview/http://localhost:4321/computer-networks/data-link-layer-overview/Framing, error detection, and medium access — what the link layer adds on top of raw signal.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptLink Layerdata-linkframingerror-detectionmaclayer-2http://localhost:4321/computer-networks/dhcp/http://localhost:4321/computer-networks/dhcp/DISCOVER / OFFER / REQUEST / ACK. The four-way handshake that gets your laptop an IP address.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockNetwork Layerdhcpnetwork-layerconfigurationbootphttp://localhost:4321/computer-networks/distance-vector-routing-rip/http://localhost:4321/computer-networks/distance-vector-routing-rip/Bellman-Ford on the control plane — each router advertises distances to its neighbours, count-to-infinity, split-horizon, poison-reverse, and why RIP capped at 15 hops.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockNetwork Layerroutingripdistance-vectorbellman-fordhttp://localhost:4321/computer-networks/email-smtp-pop-imap/http://localhost:4321/computer-networks/email-smtp-pop-imap/Three protocols for one job. Why SMTP is push, POP/IMAP are pull, and where modern alternatives took over.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockApplication Layeremailsmtpimappopapplication-layerhttp://localhost:4321/computer-networks/dns-hierarchy-and-records/http://localhost:4321/computer-networks/dns-hierarchy-and-records/Root → TLD → authoritative → recursive; A / AAAA / CNAME / MX / NS / TXT; the recursive resolution walk.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockApplication Layerdnsname-resolutionapplication-layerinfrastructurehttp://localhost:4321/computer-networks/encapsulation-and-headers/http://localhost:4321/computer-networks/encapsulation-and-headers/How a packet picks up headers on the way down and sheds them on the way up — the mental model for every layered protocol.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptFoundationsencapsulationheaderslayered-modelpacket-anatomyhttp://localhost:4321/computer-networks/ethernet/http://localhost:4321/computer-networks/ethernet/Preamble + dst + src + EtherType + payload + FCS; the switch fabric; VLAN tagging (802.1Q); the spanning tree.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockLink Layerethernetswitchingvlanlayer-2802-1qhttp://localhost:4321/computer-networks/facebook-2021-bgp-outage/http://localhost:4321/computer-networks/facebook-2021-bgp-outage/A maintenance command withdrew BGP routes for Facebook's nameservers; 6+ hours of global outage; the lessons on out-of-band access.Sun, 24 May 2026 00:00:00 GMTFoundationalpostmortemSystems & Postmortemsbgpdnsfacebookmetaglobal-outageout-of-bandhttp://localhost:4321/computer-networks/icmp/http://localhost:4321/computer-networks/icmp/ping, traceroute, destination-unreachable, time-exceeded, redirect — how the network tells you what went wrong.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockNetwork Layericmpnetwork-layerdiagnosticspinghttp://localhost:4321/computer-networks/interdomain-routing-bgp/http://localhost:4321/computer-networks/interdomain-routing-bgp/Path-vector routing between ASes, policy-based selection, the trust model that makes BGP both essential and fragile.Sun, 24 May 2026 00:00:00 GMTAdvancedbuilding-blockNetwork Layerbgproutinginterdomainpath-vectorinternet-routinghttp://localhost:4321/computer-networks/intradomain-routing-ospf/http://localhost:4321/computer-networks/intradomain-routing-ospf/Link-state routing inside an AS, Dijkstra's algorithm, hello protocol, area hierarchies — the routing protocol of enterprises and ISPs.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockNetwork Layerospfroutinglink-statedijkstrahttp://localhost:4321/computer-networks/ip-v6/http://localhost:4321/computer-networks/ip-v6/128-bit addresses, simplified header, no fragmentation by routers, IPv4 exhaustion as the forcing function.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockNetwork Layeripv6network-layeraddressingslaachttp://localhost:4321/computer-networks/mac-and-csma/http://localhost:4321/computer-networks/mac-and-csma/Stochastic medium access: listen, defer, transmit, detect collisions. The mechanism behind classic Ethernet and Wi-Fi.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockLink Layermaccsmacsma-cdcsma-cawirelesshttp://localhost:4321/computer-networks/nat-and-firewalls/http://localhost:4321/computer-networks/nat-and-firewalls/Why everyone is behind a NAT, how it breaks the end-to-end principle, and the firewall stances (stateful vs stateless) you'll meet.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockNetwork Layernatfirewallnetwork-layersecurityhttp://localhost:4321/computer-networks/network-types-by-medium-and-scope/http://localhost:4321/computer-networks/network-types-by-medium-and-scope/Guided vs unguided media, LAN/MAN/WAN/PAN, and the standard topologies (bus, ring, star, mesh) you'll still meet in datacenters.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptFoundationsnetwork-typestopologylan-wantaxonomyhttp://localhost:4321/computer-networks/python-sockets-tcp/http://localhost:4321/computer-networks/python-sockets-tcp/socket() + connect/listen/accept + sendall/recv. Custom framing, blocking vs non-blocking, the patterns that scale.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockTools & Practicepythonsocketstcpframingprogramminghttp://localhost:4321/computer-networks/python-sockets-udp/http://localhost:4321/computer-networks/python-sockets-udp/socket() + bind() + sendto/recvfrom. The simplest network programs that teach the model.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockTools & Practicepythonsocketsudpdatagramprogramminghttp://localhost:4321/computer-networks/reliable-data-transfer/http://localhost:4321/computer-networks/reliable-data-transfer/Stop-and-wait → Go-Back-N → Selective Repeat. The recipe TCP refines into its flow- and congestion-control machinery.Sun, 24 May 2026 00:00:00 GMTIntermediateconceptTransport Layerarqsliding-windowgo-back-nselective-repeattransport-layerhttp://localhost:4321/computer-networks/spanning-tree-protocol/http://localhost:4321/computer-networks/spanning-tree-protocol/How a switched LAN avoids loops — BPDUs, root-bridge election, port roles, blocked links — and why RSTP and MSTP exist.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockLink Layerstprstpbpdulayer-2-loopsswitchinghttp://localhost:4321/computer-networks/syn-floods-and-retransmission/http://localhost:4321/computer-networks/syn-floods-and-retransmission/Half-open connections, SYN cookies, retransmission timeouts — the security and resilience knobs on TCP.Sun, 24 May 2026 00:00:00 GMTIntermediateconceptTransport Layersyn-floodtcpsecurityddossyn-cookieshttp://localhost:4321/computer-networks/tcp-congestion-control-aimd-slow-start/http://localhost:4321/computer-networks/tcp-congestion-control-aimd-slow-start/The four canonical algorithms (slow start, congestion avoidance, fast retransmit, fast recovery) and why AIMD converges to fairness.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockTransport Layertcpcongestion-controlaimdslow-startcubicbbrhttp://localhost:4321/computer-networks/tcp-flow-control/http://localhost:4321/computer-networks/tcp-flow-control/The receive window, advertised window, zero-window probes, and the window-scaling option that fixed the 64KB limit.Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockTransport Layertcpflow-controlwindow-scalingreceive-windowtransport-layerhttp://localhost:4321/computer-networks/tcp-ip-model/http://localhost:4321/computer-networks/tcp-ip-model/Four layers (link, internet, transport, application) and the reason the Internet runs on them instead of OSI.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptFoundationstcp-iplayered-modelfundamentalsnetworking-basicshttp://localhost:4321/computer-networks/udp/http://localhost:4321/computer-networks/udp/Connectionless, unreliable, lightweight. The header, the checksum, and the cases where UDP is the right answer.Sun, 24 May 2026 00:00:00 GMTFoundationalbuilding-blockTransport Layerudptransport-layerdatagramdnsquichttp://localhost:4321/computer-networks/what-is-the-internet/http://localhost:4321/computer-networks/what-is-the-internet/An internet of internets — autonomous systems, end hosts, routers, the IP datagram contract that holds it together.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptFoundationsinternetautonomous-systemsipfundamentalshttp://localhost:4321/computer-networks/what-is-the-transport-layer/http://localhost:4321/computer-networks/what-is-the-transport-layer/End-to-end delivery over an unreliable IP network. Multiplexing, demultiplexing, and the reliability spectrum.Sun, 24 May 2026 00:00:00 GMTFoundationalconceptTransport Layertransport-layermultiplexingtcpudpfundamentalshttp://localhost:4321/computer-networks/wifi-802-11/http://localhost:4321/computer-networks/wifi-802-11/PHY layers (a/b/g/n/ac/ax/be), CSMA/CA, association, hidden terminals, RTS/CTS, the security generations (WEP→WPA→WPA3).Sun, 24 May 2026 00:00:00 GMTIntermediatebuilding-blockLink Layerwifi802-11wirelesswpacsma-cahttp://localhost:4321/computer-networks/http-fundamentals/http://localhost:4321/computer-networks/http-fundamentals/The protocol most engineers know best. Methods, status families, the headers that actually matter, persistent connections.Sun, 17 May 2026 00:00:00 GMTFoundationalbuilding-blockApplication Layerhttpapplication-layerwebresthttp://localhost:4321/computer-networks/ip-v4-fundamentals/http://localhost:4321/computer-networks/ip-v4-fundamentals/32-bit addresses, classless inter-domain routing (CIDR), subnet masks, fragmentation, the IPv4 header.Sun, 17 May 2026 00:00:00 GMTFoundationalbuilding-blockNetwork Layeripv4network-layercidrsubnettinghttp://localhost:4321/computer-networks/osi-model/http://localhost:4321/computer-networks/osi-model/Seven layers, what each one is for, why nobody actually deploys all seven, and where the model still helps reasoning.Sun, 17 May 2026 00:00:00 GMTFoundationalconceptFoundationsosilayered-modelfundamentalsnetworking-basicshttp://localhost:4321/computer-networks/tcp-fundamentals/http://localhost:4321/computer-networks/tcp-fundamentals/Three-way handshake, four-way close, sequence/ack numbers, the flags (SYN/ACK/FIN/RST/PSH/URG), what each enables.Sun, 17 May 2026 00:00:00 GMTFoundationalbuilding-blockTransport Layertcptransport-layerhandshakereliabilityhttp://localhost:4321/computer-networks/tools-ping-traceroute-tcpdump/http://localhost:4321/computer-networks/tools-ping-traceroute-tcpdump/The six commands you actually use to debug networks. Read packets, follow paths, resolve names, talk HTTP.Sun, 17 May 2026 00:00:00 GMTFoundationalbuilding-blockTools & Practicedebuggingclitcpdumptracerouteobservability