Classify any IPv4 or IPv6 address by its leading bits (private, loopback, link-local, documentation, public), read CIDR /N to predict host count, and compress an IPv6 address to canonical form with a single ::.

Run ifconfig and one line reads inet 192.168.1.42, which looks like four small numbers with dots between them. It is really one 32-bit integer, and its leading bits alone already say whether it can leave your machine at all.

Name the four numbers that identify a TCP connection, predict whether two bind() calls collide before running them, and read a TIME_WAIT row in ss as an address still held after close.

ss -tn on a machine serving traffic prints dozens of rows, and every one shows 10.0.0.5:443 on the left with a different address on the right. One slot, dozens of live conversations, and the right column is why.

Separate the stub's single query from the recursive's walk down the root, TLD, and authoritative chain, read a dig +trace block by block, and predict when a repeat lookup skips the walk from cache.

dig example.com prints one answer in a few milliseconds, but dig +trace example.com prints three screens of servers handing you off, each one saying ask them instead until the last one finally answers.

Read a dig answer line as five fields, match A, AAAA, CNAME, MX, and TXT to the payload each carries, and predict how long a record change takes to clear every cache from the TTL already in flight.

dig example.com prints one line: a name, a couple of numbers, and an address. Change that address at the source and half the internet keeps handing out the old one for hours, each server on its own clock.

Trace the hosts: line of /etc/nsswitch.conf to predict which source answers a name, distinguish an /etc/hosts override that ping honors from one dig ignores, and read the [NOTFOUND=return] bracket that keeps .local names off your ISP's resolver.

Add one line to a file on your disk and ping app.example answers with the address you picked. Run dig app.example right after and it ignores that line entirely, going straight to the network instead.