Networking · Lesson 19 of 26 · 8 minutes

Firewall port inventory

Compare firewall rules to a port inventory file.

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Your objectives

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1
Show firewall
Run ufw status verbose.
Hint & worked example
Inspect or adjust the training firewall rule list. No real firewall changes occur.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
ufw status verbose
```
Remember: Firewall rules should be scoped and reviewed; simulator access is not a production change approval.
2
Unique port inventory
Run cat data/ports.txt | sort | uniq.
Hint & worked example
Read one or more files to standard output without editing their contents. Order lines before comparing or grouping them; -n compares numerically and -r reverses order. Collapse adjacent duplicate lines; use sort first when duplicates are not already together.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
cat data/ports.txt | sort | uniq
```
Remember: Reading a source file should precede changing it; avoid printing real secrets. Alphabetical sorting is not numeric sorting. uniq does not find every duplicate in an unsorted stream.
3
Find telnet port
Run grep 23 data/ports.txt.
Hint & worked example
Select input lines that match a pattern; -i ignores case, -n adds line numbers, and -v inverts selection.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
grep 23 data/ports.txt
```
Remember: No matches is exit status 1, which is different from a malformed invocation.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

ufw: Inspect or adjust the training firewall rule list. No real firewall changes occur.
Firewall rules should be scoped and reviewed; simulator access is not a production change approval.
cat: Read one or more files to standard output without editing their contents.
Reading a source file should precede changing it; avoid printing real secrets.
sort: Order lines before comparing or grouping them; -n compares numerically and -r reverses order.
Alphabetical sorting is not numeric sorting.
uniq: Collapse adjacent duplicate lines; use sort first when duplicates are not already together.
uniq does not find every duplicate in an unsorted stream.
grep: Select input lines that match a pattern; -i ignores case, -n adds line numbers, and -v inverts selection.
No matches is exit status 1, which is different from a malformed invocation.

Worked example and expected result

$ ufw status verbose

Status: active
Logging: on (simulated)
Default: deny incoming, allow outgoing
- allow 22/tcp
- allow 80/tcp
- allow 443/tcp
- deny 23/tcp

Exit status: 0. The command completed successfully in the training fixture.

$ cat data/ports.txt | sort | uniq

Exit status: 0. The command completed successfully in the training fixture.

$ grep 23 data/ports.txt

Exit status: 0. The command completed successfully in the training fixture.

Try a variation

Repeat this workflow in the sandbox with a different scratch filename. Keep the system fixtures unchanged and compare the observed output with your expectation before moving on.

Explain it

In “Firewall port inventory”, which interpretation is safe?Reading a source file should precede changing it; avoid printing real secrets.A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.

Apply it elsewhere

Before adapting the cat workflow from “Firewall port inventory” to another server, what should you do?Paste the training paths unchanged into production.Skip output inspection whenever the command is familiar.Confirm the current directory, target identity, permissions, and the installed command behavior first.

Keep the momentum.

Complete the lab, then explain and apply the pattern.

Next: SSH dry-run review Try an incident drill

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