Theory alone does not carry networking — the concepts stay abstract until you actually see a packet in Packet Tracer or Wireshark. The sysadmin material here is organised around certification syllabi, which turns it into an ordered plan.
75 links
A Mozilla article that uses cartoons to explain why DNS is a privacy problem and how DoH changes it. Unlike protocol specs it assumes no background and quickly shows what the DoH debate is about.
Takes and restores sector-level disk images. Unlike file backup it copies everything bit for bit, operating system and boot record included.
The most comprehensive free reference on Bash scripting, every topic with a runnable example. Compared with the Wooledge BashGuide its coverage is still unmatched, but its style is dated and some examples now count as bad habits.
A project bringing mainline Linux to Apple Silicon Macs, reverse-engineering the GPU driver and power management. Unlike a virtual machine it runs on the metal, so you get the M-series chip’s full performance.
A list of Arch Linux–based distributions and projects. Unlike the Arch Wiki, it collects not documentation but the distributions derived from Arch and their tools, side by side.
A resource list for eBPF, which runs safe programs inside the kernel. Unlike writing a kernel module, the program must first pass the verifier, so it runs without the risk of crashing the kernel.
A list of eBPF projects, articles and tools, with compilers, tracing and networking (XDP) under separate headings. Unlike the other eBPF list already in the directory it is still being updated, and is kept by someone who writes eBPF documentation.
A list of apps and extensions for the GNOME desktop environment. Unlike the KDE list, it covers GTK/libadwaita apps that follow GNOME’s interface guidelines, plus shell extensions.
A list of tools and projects for IPFS, the decentralised file protocol. Unlike HTTP, it addresses a file by the hash of its content (CID) rather than by the server that holds it.
A list of apps and resources for the KDE desktop environment. Unlike the GNOME list, it focuses on Qt-based KDE apps and Plasma customisation.
A list of tools and examples for Scapy, the Python packet-manipulation library. Unlike general network lists it centres on crafting and sending packets by hand.
A list of recommended apps and tools for the Windows desktop. Unlike the Microsoft Store it is curated and puts free and open-source options first.
An introduction to shell scripting. Unlike the Advanced Bash-Scripting Guide, it lays the groundwork without that guide’s weight.
Bash’s official manual. Unlike tutorials, it has the final word on contested topics such as expansion rules and parameter substitution.
A Bash guide centred on the most common mistakes, such as quoting and word splitting. Unlike older sources such as the Advanced Bash-Scripting Guide, it was written to correct the bad examples circulating online.
A video working networking concepts from the OSI layers through routing in full-course format. Unlike exam-driven certification courses it builds concepts without tying them to objectives — groundwork before certification study.
The blog and tools of a widely cited expert on Linux performance and observability. Unlike general guides it gives kernel-level measurement and flame-graph methods.
A service that bridges websites, the fediverse (Mastodon etc.) and Bluesky/AT Protocol so accounts can follow and reply across networks. Unlike single-network clients, it translates between the protocols themselves.
A minimal check for whether a given port is reachable from outside. Unlike scanning locally it looks in from the internet, which is the only way to tell whether router port forwarding actually works.
The CCSA and CCSE certifications. What differs from other firewall vendors is that Check Point’s management architecture is its own body of knowledge — centralised policy management sits at the centre of the training.
A reference site that lists every TLS cipher suite searchably, with IANA and OpenSSL names, a security rating (secure/weak/insecure) and protocol-version support. For when you meet a suite name and want to know what it means and whether to allow it. Unlike the raw IANA registry, it gives each suite a readable security rating.
Cisco’s official networking curriculum, with part of the CCNA track free. Unlike video courses it comes with Packet Tracer labs, so you test the theory by building topologies.
The networking certification programme from CCNA to CCIE. Unlike vendor-neutral certificates it is specific to Cisco equipment; even so, CCNA is widely treated as a solid networking fundamentals curriculum regardless of vendor.
Datasheets for the SG500 series. Unlike a single model’s manual, they compare port counts, PoE budgets and stacking support — the differences you need when buying second-hand.
First-time setup of one specific switch model, screenshot by screenshot. Unlike the official manual, it shows the practical details that manual skips.
An archive of user-submitted UNIX one-liners ranked by vote. Unlike per-tool summaries such as tldr, you search by task — to check whether a shortcut exists.
The site for the standard command-line tool for transferring data with URLs and for the libcurl library; it has the manual, a protocol list and the free book "Everything curl". With "copy as cURL" in browser dev tools it is the basic way to debug an API call. It makes a request repeatable from the command line, instead of living only in browser dev tools.
Send a test email to the temporary address it gives you and it reports SPF, DKIM and SpamAssassin scores. Instead of checking records in isolation, it tests a real message end to end.
Verisign's tool that validates a domain's DNSSEC chain of trust from the root down and shows where it breaks. Unlike general DNS checkers it concentrates on the signature chain alone.
The NSE programme and security training. Against other vendor programmes most of it has been made free — the broadest no-cost resource for firewall and network security fundamentals.
A bootable Windows PE environment for systems that will not start, bundling disk cloning, password reset and data recovery in one image. Unlike Linux-based rescue disks it offers a familiar Windows interface and runs Windows tools.
Domain registration lookup through ICANN’s own interface. Against third-party WHOIS sites there are no ads and no sales pitch — you do not get an email the next day about the domain you looked up.
A Cloudflare page that tests from your browser whether your ISP filters invalid BGP routes (RPKI). It turns an abstract topic, routing security, into a one-click result. Unlike the technical RPKI documentation, it gives you the answer in one click from your browser.
Junos-based networking certifications. Against Cisco’s programme the entry-level exams have long been offered free and the training material is open — the no-cost route into networking.
Teaches Linux in small modules — filesystem, permissions, processes, package management. Unlike comprehensive books, it offers digestible pieces with exercises at the end of each lesson.
Distribution-neutral Linux certifications (LPIC-1, LPIC-2). Against Red Hat’s programme it is not tied to one distribution — this is the certificate that still applies if you run Debian, SUSE or Arch.
Teaches the command line from nothing and carries you into shell scripting; the home of "The Linux Command Line". Against a list of commands it follows a path — a sequenced course rather than a scattered cheat sheet.
An explorer visualising Bitcoin’s pending transaction pool and the chain, runnable against your own node. Against other block explorers it adds fee estimation and a mempool view — it shows how congested the network is right now.
Looks up an IP or domain in hundreds of DNS blocklists (RBLs) at once. Shows which list is behind a mail server being rejected, and also checks forward and reverse DNS consistency. Rather than checking one blocklist, it queries hundreds of RBLs at once.
An email and DNS diagnostic that runs MX, DNS, blacklist, SPF, DMARC, ping and port lookups from a single box. A common first stop for mail delivery problems, replacing several single-purpose checkers. Unlike single-purpose checkers, it runs MX, SPF, DMARC and blacklist lookups from one box.
The Turkish catalogue of Cisco networking courses, with free entry-level classes that award badges. Turkish-language networking training is not easy to find locally.
A wildcard DNS service that resolves names like 10.0.0.1.nip.io to the IP embedded in them, so you can reach a local or test server by hostname without editing the hosts file. No setup or sign-up. Instead of editing /etc/hosts, it embeds the address in the name itself.
The source of cryptographic standards, where you check which algorithms remain approved; the post-quantum selections were published here too. Unlike blog posts, it is the binding official source.
A map rendering power lines, plants, oil/gas pipelines and telecom infrastructure from OpenStreetMap data. Unlike general maps, it has infrastructure-specific layers with voltage and capacity detail.
A browser-based speed test needing no Flash and no app, and self-hostable on your own server. That self-hosting is the difference from Speedtest.net: you can measure your LAN’s real throughput without an internet hop.
The official site of the TLS/SSL and general-purpose cryptography library and the openssl command-line tool; command manuals, release notes and library API docs live here. The basic reference for generating certificates, converting keys and inspecting a handshake against a server. It is a library as well as a command tool, so it covers more than single-purpose certificate utilities.
A step-by-step guide to building a root and intermediate certificate authority with OpenSSL, signing certificates and publishing revocation lists. Unlike ready-made CA software it shows the file layout and configuration by hand, so you see how a PKI works.
Turns the operating system into something you query with SQL — running processes, open ports and installed packages become tables. Instead of separate commands such as ps and netstat, you ask everything in one query language; common in endpoint monitoring.
The Packet Tracer download plus lab files, letting you practise VLAN, OSPF and ACL configuration without buying switches and routers. Unlike GNS3 it is a simulator — no real IOS images needed, but command coverage is limited.
PCNSA and PCNSE certifications with firewall and cloud security training. Against Fortinet it targets the upper enterprise segment — the certificate pays off directly at organisations running those products.
Free video courses covering the whole CompTIA A+, Network+ and Security+ syllabus; course notes and practice exams are paid. Unlike general networking courses, every lesson is numbered one to one against the exam objectives.
A collection of ways to do things with Bash’s own facilities instead of calling external programs, which speeds scripts up markedly by removing sed and awk calls. The repository is archived (last update November 2023); the techniques rest on Bash itself so most still hold, but nobody closes issues any more.
The RHCSA and RHCE certifications. Unlike multiple-choice vendor exams these are entirely practical — you complete tasks on a live system, which is why they carry weight on the Linux side.
RIPE NCC's network of thousands of small probes that run ping, traceroute and DNS measurements from around the world. It lets you see a target from other countries and operators rather than your own connection, which helps diagnose reachability problems.
An introduction to Linux and Bash with exercises closing every section. Against LinuxCommand.org it is shorter and more drill-oriented — for getting through the basic commands quickly.
Simulates working a real helpdesk queue — prioritisation, escalation, SLA tracking. Unlike IT support courses that stay theoretical, it has you practise the job.
TeleGeography's interactive map of the world's submarine internet cables, landing points and owners. Unlike generic network maps it makes the physical backbone of the internet traceable cable by cable.
Community-maintained Turkish wiki covering Ubuntu and GNU/Linux system administration, package management, networking, and hardware troubleshooting; organizes step-by-step guides instead of scattered forum threads.
A toolbox of dozens of DNS and domain queries in one place: reverse IP lookup, DNS history, whois, a port scanner, domain-to-IP mapping. Each query is a small separate tool and no sign-up is needed.
A checker that runs a domain's DNS setup (delegation, SOA, DNSSEC, nameserver consistency) through dozens of tests; the open-source engine of the Swedish registry. Unlike tools that query one record, it reports on the whole zone against a standard test suite.