# Knowledge Check: Networking Mental Model

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**1. What's the actual difference between an IP address and a port?**

*Answer:* An IP address identifies a specific machine on a network; a port identifies WHICH
service on that machine, since one IP can host many services simultaneously.

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**2. `curl` reports "Could not resolve host." Which layer failed?**

*Answer:* DNS — the name never got translated into an IP address, so no connection attempt was
even made.

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**3. `curl` reports "Connection refused" instead. What does that specifically tell you?**

*Answer:* The name resolved fine and the destination was reachable, but nothing is listening on
the port you tried — the connection attempt was actively rejected, not silently ignored.

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**4. What is a default gateway for?**

*Answer:* It's where your machine sends traffic whose destination ISN'T in its own local subnet
— effectively "ask this router to figure out how to get there."

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**5. True or false: `0.0.0.0` is a real destination address you could `curl`.**

*Answer:* False (in the way most students initially assume) — when a SERVICE binds to
`0.0.0.0`, it means "listen on every interface," a bind convention, not a real host you'd
connect to as a destination.

## Instructor Notes

**Facilitation:** Questions 2-3 are worth spending real time on together — the point isn't
memorizing the exact error text, it's the underlying "which layer does this rule out" reasoning.

**Approximate timing:** 8 minutes (slightly longer than a typical knowledge check, given this
module's weight).