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Recap: Ports

Lesson 14 of 47 in Coddy's Networking with the Terminal course.

The address is the machine, the port is the program on it, and the two together are a socket.

Servers listen, clients connect, and only one program can listen on a given port at a time.

python3 -m http.server 9108 &   # listen
nc -z 127.0.0.1 9108             # is anything there?
curl -s http://127.0.0.1:9108/   # connect and ask

Worth remembering: 22 SSH, 53 DNS, 80 HTTP, 443 HTTPS, and that ports under 1024 normally need administrator rights.

And the two failures that mean different things: refused is reachable but nothing listening, timeout is nothing answered at all.

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Challenge

Medium

Put the whole chapter together: listen, check, connect.

  1. Create a file index.html containing exactly ports are doors
  2. Serve the folder on port 9108 in the background
  3. Fetch http://localhost:9108/index.html with curl -s

Expected output:

ports are doors

Use the name localhost rather than the address, to prove it resolves.

Try it yourself

Terminal
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This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Networking with the Terminal

1How Networks Talk

What Is a NetworkClients and ServersIP AddressesYour First Request

4Is It Reachable?

ICMP and pingReading Ping OutputWhen Ping LiesRefused or Timed OutRecap: Reachability

7Sending Data

POST with -dWhat -d Actually SendsForm EncodingSending JSONPUT and DELETERecap: Writing Data

2Names and DNS

Why Names ExistThe Hosts FileLooking Up a NameRecord TypesRecap: Names

5HTTP by Hand

Anatomy of a RequestRequest MethodsStatus CodesResponse HeadersWriting a ResponseRecap: HTTP Basics

8HTTPS and TLS

Why HTTPSThe Scheme Picks the PortCertificates and TrustWhen TLS FailsRecap: HTTPS

3Ports and Sockets

What Is a PortWell-Known PortsLocalhostListening vs ConnectingRecap: Ports

6curl in Depth

Seeing the HeadersSaving ResponsesCustom HeadersStatus and Timingcurl Exit CodesRecap: curl Flags

9Auth and Debugging

API Keys and BearerThe User AgentTimeouts and RetriesReading a FailureRecap: Debugging

Practice on your own: Terminal playground