← ACARA Digital Technologies Years 9–10

Domain table (name-to-address table)

A list pairing each domain name with an IP address. A DNS server looks up a name in it. A missing or wrong entry sends users to the wrong place or nowhere.

Part of: ACARA Digital Technologies Years 9–10 — Networked Systems and Access Control — Module 32

Understanding Domain table (name-to-address table) in ACARA Digital Technologies Years 9–10

What it does: The code looks up a name in the table and gets the IP address stored for it, which is exactly what a DNS server does. A domain table is a list of domain names and the IP addresses they point to. A DNS server uses it to look names up. Each row pairs a name with the IP address a browser should connect to. A missing entry means the DNS server has no IP address to give, so the traffic goes nowhere. A wrong entry redirects users to the wrong place. This is the idea behind pharming. Pharming changes where a name points. Sending a fake email is phishing.

Common mistakes: An IPv4 number can only go up to 255, so 310 is not a valid address. The entry should be 203.0.113.10, otherwise the DNS server has no real address to return. Computers send data to an IP address, not a name. When an entry is found, the request must go to the stored address from the table.

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Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 12–34) and word search (Modules 12–55).

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Learning
Duo
What does a domain table pair together?
Each domain name with an IP addressEach IP address with a MAC address
Matches
games.example.com → 203.0.113.300
↓
The table entry has an invalid IP address because 300 is above 255. The name can never be matched to a real device.
Applying
Meanings
Term
domain table
Meaning
A list pairing each domain name with an IP address. A DNS server looks up a name in it. A missing or wrong entry sends users to the wrong place or nowhere.
Practice
school.edu.au -> 203.0.113.10
Testing
Gaps
lookup school.edu.au ->
Check Answer
Spots
1school.edu -> 203.0.113.310
2shop.com.au -> 198.51.100.7

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Quick Questions

1. What does a domain table pair together?
A. Each domain name with an IP address ✓
B. Each IP address with a MAC address
A domain table is a list of domain names and the IP addresses they point to. A DNS server uses it to look names up.
2. A DNS server gets a request for shop.example.com. What does it do first?
A. Looks the name up in its domain table ✓
B. Sends the request straight to the router's MAC address
The DNS server searches its domain table for the name so it can reply with the matching IP address.
3. The table has the row: school.edu.au | 203.0.113.8. What is 203.0.113.8?
A. The password for school.edu.au
B. The IP address for school.edu.au ✓
Each row pairs a name with the IP address a browser should connect to.
4. A student types a domain name that is NOT in the DNS server's domain table. What is the most likely result?
A. The page will not load because no address is found ✓
B. The page loads faster from a backup table
A missing entry means the DNS server has no IP address to give, so the traffic goes nowhere.
5. The table lists bank.com.au with the IP address of a scammer's server. What happens when users visit bank.com.au?
A. They still reach the real bank safely
B. They are sent to the wrong server ✓
A wrong entry redirects users to the wrong place. This is the idea behind pharming.

Match the Pairs

shop.example.com → 203.0.113.15 → A domain table entry that pairs the name shop.example.com with the IP address 203.0.113.15
lookup("school.edu.au") → not found → The domain table has no entry for this name, so the DNS server cannot give back an IP address
A DNS server reads a domain table to find the IP address that matches a name → table["mail.example.com"] = "198.51.100.7"
A wrong entry can redirect users to a fake site (pharming) → bank.example.com → 192.0.2.99 (attacker's server)
games.example.com → 203.0.113.300 → The table entry has an invalid IP address because 300 is above 255. The name can never be matched to a real device.
news.example.com → 192.0.2.50 (should be 203.0.113.8) → The table holds the wrong IP address for this name, so users who type the correct name land on a different server.

Key Term

domain table
A list pairing each domain name with an IP address. A DNS server looks up a name in it. A missing or wrong entry sends users to the wrong place or nowhere.

Fill in the Blanks

1. school.edu.au 203.0.113.5 lookup school.edu.au -> 203.0.113.5
Hint: Type the IP address that the table pairs with this domain name.
2. shop.com.au 198.51.100.7 lookup news.com.au -> NOT FOUND
Hint: Type the two-word result in capitals when the table has no entry for the name.
3. bank.com.au 203.0.113.66 real bank IP: 203.0.113.10 Users are sent to the wrong server
Hint: Type the word that describes where a bad entry sends users.
4. games.com.au 192.0.2.44 mail.com.au 192.0.2.45 lookup mail.com.au -> 192.0.2.45
Hint: Type the domain name in the table that is paired with this IP address.
5. A DNS server looks up a name in the domain table to find its IP address
Hint: Type the name of the list that pairs domain names with IP addresses.

Spot the Error

Question 1
A school.edu -> 203.0.113.310
B shop.com.au -> 198.51.100.7
C news.com -> 192.0.2.44
Line A — An IPv4 number can only go up to 255, so 310 is not a valid address. The entry should be 203.0.113.10, otherwise the DNS server has no real address to return.
Question 2
A name ← 'shop.com.au'
B IF name is in the table
C SEND to the name typed
D ELSE
E SHOW 'not found'
Line C — Computers send data to an IP address, not a name. When an entry is found, the request must go to the stored address from the table.
Question 3
A bank.com.au -> 192.0.2.10
B mail.com.au -> 192.0.2.11
C game.com.au -> 192.0.2.12
D shop.com.au ->
Line D — This entry has a name but no IP address, so it is effectively a missing entry. The lookup for shop.com.au would lead nowhere. It should be shop.com.au -> 192.0.2.13.
Question 4
A # Real bank site: 192.0.2.10
B bank.com.au -> 198.51.100.99
C # Wrong entry = wrong site
Line B — The entry does not match the real bank address of 192.0.2.10. A wrong entry like this redirects users to another server, which is how pharming works.
Question 5
A table ← domain table
B ip ← table['192.0.2.50']
C OPEN ip
Line B — A domain table is searched by domain name, not by IP address. The lookup should use the name 'cafe.com.au' to get the address.

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