Networking

The seven layers networking gets described in, the four-layer model the internet actually uses, what happens to one request on its way down and back up, and how to use the layers to troubleshoot.

An IPv4 address is one 32-bit number, and the /n in CIDR notation says how many of those bits are locked.

The steps between typing a name and connecting to an address, who answers each question along the way, why changes take time to show up, and where Route 53 fits.

A hosts-file line or an SSH config alias can point a name at a machine without touching DNS. How each works, which to use, and how to tell a naming problem from a network one.

Layer 4 vs. layer 7, NLBs vs. ALBs, what it means to terminate TLS, and how to put HTTPS in front of a single server without a load balancer at all.

What a TLS certificate is, how keys and signatures make it trustworthy, what root, intermediate, and leaf certificates are for, how you get one, and what to do when a client refuses to trust it.

The first few messages of every HTTPS connection, where the browser checks who it's talking to and the two sides agree on a secret key in public, plus what's different in TLS 1.2, what someone watching can still see, and how to watch it happen.

How a VPC is carved into subnets, how route tables make a subnet public or private, how security groups and network ACLs filter traffic, and how to lay it all out.

The ways into a private network, from connecting whole networks with VPNs and Transit Gateway to forwarding one port for an afternoon, and what to check when you're connected but still can't reach anything.

How machines share folders over a network with SMB and NFS, how a NAS differs from a SAN or a local disk, which ports each one needs and which way the connections go, and why port 445 never belongs on the internet.