The previous chapter covered the fundamentals: the options, the basic filter primitives, and the output formats. This chapter covers the filters and techniques that turn tcpdump from a packet printer into a diagnostic instrument. The BPF filter language can match the specific fields inside the packet—the TCP flags, the ICMP type, the packet length, the…
tcpdump is the command-line packet analyzer that captures the traffic on a network interface and prints a summary of each packet. It is the tool that turns the abstract network into observable data: the TCP handshake, the DNS query, the HTTP request, the ICMP error. The previous chapters covered the firewall and the VPN, which…
The previous chapter covered the concepts: the tailnet, the coordination service, and the data plane. This chapter is the operational sequence. It covers the installation, the authentication, the mesh connectivity that connects every device to every other device, and the three routing features that extend the tailnet beyond its own devices: the subnet router, the…
Tailscale is a mesh VPN built on top of WireGuard. It takes the encrypted peer-to-peer tunnels that WireGuard provides and adds the coordination layer that WireGuard deliberately leaves out: identity-based authentication, automatic key distribution, NAT traversal, and a centralized control plane that tells every device how to reach every other device . The previous chapters…
OpenVPN setup is a sequence of dependent steps: the PKI must exist before the certificates can be generated, the certificates must exist before the server can start, and the server must be reachable before the client can connect. The previous chapter covered the control and data channels that make the protocol work; this chapter covers…
Installation Package Purpose zustand Core store, hooks, middleware immer Required for immer middleware zustand/middleware Built-in middleware (persist, devtools, immer) Requirement Value React version 18.0+ TypeScript syntax create<T>()(…) (curried, v5) Provider Not required Creating a Store Rule Detail Curried syntax create<T>()(…) — double parentheses Module scope Store created once, outside components set behavior Shallow merge get…
A Zustand store is a plain JavaScript object with functions, which makes it simpler to test than a React component. The store does not need a provider, does not need to be rendered, and does not depend on the React lifecycle. The test calls the store’s actions directly, reads the state with getState(), and asserts…
A transient update is a subscription to a Zustand store that reads the state without causing the component to re-render. The useStore hook re-renders the component when the selected value changes, and that is the behavior that most components need. But some components need to react to a change without rendering—a canvas that redraws itself,…
Installation Package Command Purpose Core npm install @tanstack/react-query Required DevTools npm install -D @tanstack/react-query-devtools Development only ESLint plugin npm install -D @tanstack/eslint-plugin-query Optional quality Requirement Value React version 18.0+ (v5) v4 for React 17 npm install @tanstack/react-query@4 v5 hook syntax Object only: useQuery({ queryKey, queryFn }) v4 → v5 rename cacheTime → gcTime v4 →…
Testing a TanStack Query hook is not the same as testing a plain React hook. The hook depends on a QueryClient that lives in React context, and it performs asynchronous network requests that resolve after the test’s synchronous assertions have finished. A test that renders the hook without a provider throws immediately. A test that…