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Recap: Reachability

Lesson 19 of 47 in Coddy's Networking with the Terminal course.

Diagnosis is a ladder, and each rung rules something out.

Is the machine there? Ping it. Remember that a failed ping proves little, since many hosts ignore ICMP.

Is the port open? nc -z. This is where "the server is up but the site is down" gets caught.

Is the service answering? Make a real request with curl and read the exit code: 0 worked, 7 refused, 28 timed out.

Climb in that order and each answer narrows the next question. Skipping to the top is how people end up restarting things at random.

challenge icon

Challenge

Hard

Climb the whole ladder against a server you start yourself.

  1. Create index.html containing up
  2. Serve the folder on port 9109
  3. Print 1: and the ping result (ok)
  4. Print 2: and the port result (ok)
  5. Print 3: and the page you fetched

Expected output:

1: ok
2: ok
3: up

Try it yourself

Terminal
quiz iconTest yourself

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