Networking foundations

Computer networking for people who run data platforms: what slow is made of, names and requests, the TCP connection, addresses and routes, routes between networks, one link at a time, and the secured path. Eight parts, every mechanism animated.

Part 1

Where slow comes from: four delays, the queue and the narrowest link

Every hop charges four delays, and distance sets a floor that no faster link lowers. A queue grows sharply near full load, a copy runs at its narrowest link, and a traceroute shows which of these you pay.

7 figures · 18 min

Part 2

Names, ports and requests: DNS and HTTP before the first byte

Before an API call returns its first byte, a resolver turns the name into an address, a socket opens on a port, and HTTP sends a request. Every new connection costs round trips that a kept connection and a cache save.

8 figures · 21 min

Part 3

TCP, the connection: handshake, numbers, losses and windows

TCP numbers every byte and resends what is not acknowledged, so a network that loses packets still carries one ordered stream. How fast that stream runs over a long path is at most the smaller of two windows divided by the round-trip time.

8 figures · 20 min

Part 4

Addresses, routes and NAT: what a router does to a packet

A router reads one address, takes the longest matching row of its table, lowers the TTL and sends the packet on. Subnets, DHCP and NAT decide which addresses it carries.

8 figures · 20 min

Part 5

Routes between networks: BGP, route selection and ICMP

Nobody types the route from one network to another. Routers announce prefixes with the path they took, pick by policy before path length, and use ICMP to say what went wrong.

8 figures · 19 min

Part 6

One link at a time: frames, ARP, switches and the data center

IP picks the next router; the link carries the packet there in a frame addressed to a MAC. ARP finds that address, a switch learns where it lives, and a data center connects many equal paths.

7 figures · 20 min

Part 8

Securing the path: keys, certificates, TLS, IPsec and firewalls

Every router on the path can read, change or replay a packet. TLS seals one connection after a certificate proves the server's name, IPsec seals everything between two networks, and a firewall decides who may start a connection.

7 figures · 22 min

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