OpenCyber AcademyLesson map
Lesson 10. Map, example, EX056.
flowchart TD
V["198.51.100.400"] --> P["ip_address raises"]
P --> D{"Digits only after dots are removed?"}
D -->|Yes| I["print invalid and skip"]
G["203.0.113.9"] --> OK["ip_address accepts"]
One call rejects the broken octet. A different value passes the same call.
Logical drawing
rejected
198.51.100.400
octet 400
accepted as an address
203.0.113.9
not a lookup
no DNS
no route
Learning outcomes
After this chapter, you should be able to:
- Say which call rejects
198.51.100.400. - Separate that rejection from a domain.
- Refuse a network lookup this file does not make.
10.1 The library raises. The digit test then chooses the invalid line.
ipaddress.ip_address accepts 203.0.113.9 and raises ValueError for 198.51.100.400, because 400 is above 255. The except branch then removes dots and asks whether the rest is all digits. 19851100400 is all digits, so the script prints invalid: and does not append the pair. A domain fails the address call too, but the leftover characters are not all digits, so the domain is appended instead of rejected. The digit test is how this file tells a broken address from a name. It is not a reputation check.
The header of the book already limits addresses to documentation ranges. 203.0.113.9 parses and sits in such a range. 198.51.100.400 does not parse, so it is not a host in 198.51.100.0/24. The script never asks the network which of them exists. There is no DNS call in lab_rapid.py. Visiting either name is outside the lab, and this chapter does not add a lookup.
Lesson table; scroll horizontally to read all columns →
| Value | Branch |
|---|---|
203.0.113.9 |
Accepted by ip_address |
198.51.100.400 |
Raised, then classified invalid |
| A domain with letters | Raised, then appended |
| A DNS answer | Not requested |
10.2 Worked example
Lesson table; scroll horizontally to read all columns →
| Offered claim | What the branch did | Decision |
|---|---|---|
| "400 cannot be an octet, so the line says invalid." | The raise plus the digit test | Keep |
| "203.0.113.9 is kept by the same call." | No exception | Keep |
| "The script resolved the name." | No DNS call | Refuse |
| "The invalid address is a domain because it failed." | The digit test separated it | Refuse |
Synthetic case. Both values are classroom literals.
Errors and limits
Do not go and look the rejected value up.
Apply
- EX056 — The octet. Why is
198.51.100.400invalid while203.0.113.9is kept, and does the script query DNS?Show marking criteria
Rubric: 3 = 400 is above 255 so ip_address raises; the digit test prints invalid and skips; 203.0.113.9 parses; there is no DNS call;; 2 = the octet fails and the other address parses;; 1 = one value;; 0 = none.