Private vs public IP addresses in Computer Networks - Visual Side-by-Side Comparison

Concept Flow - Private vs public IP addresses

Start

↓

Device needs IP

↓

Is device inside local network?

No→Assign Public IP

Yes↓

Assign Private IP

↓

Use NAT to connect to Internet

↓

End

This flow shows how devices get either private or public IPs depending on their network location and how private IPs use NAT to access the internet.

Execution Sample

Computer Networks

Device in home network requests IP
Is device inside local network? Yes
Assign private IP 192.168.1.5
Device accesses internet via router's public IP

Shows a device inside a home network getting a private IP and using the router's public IP to connect outside.

Analysis Table

Step	Device Location	IP Assigned	Reason	Network Access
1	Inside local network	192.168.1.5 (Private)	Private IP used for local devices	Access internet via NAT
2	Outside local network	203.0.113.10 (Public)	Public IP used for internet devices	Direct internet access
3	Inside local network	10.0.0.7 (Private)	Private IP used for local devices	Access internet via NAT
4	Outside local network	198.51.100.25 (Public)	Public IP used for internet devices	Direct internet access
5	End	-	No more devices to assign	Process stops

💡 All devices assigned appropriate IPs based on location; process ends.

State Tracker

Variable	Start	After 1	After 2	After 3	After 4	Final
Device Location	Unknown	Inside local network	Outside local network	Inside local network	Outside local network	End
IP Assigned	None	192.168.1.5	203.0.113.10	10.0.0.7	198.51.100.25	None

Key Insights - 3 Insights

Why do devices inside a local network get private IPs instead of public IPs?

Devices inside local networks get private IPs to save public IP addresses and for security. This is shown in execution_table rows 1 and 3 where private IPs are assigned.

How can devices with private IPs access the internet?

They use a process called NAT (Network Address Translation) through a router with a public IP, as shown in execution_table rows 1 and 3 under Network Access.

What is the difference between private and public IP addresses in terms of accessibility?

Public IPs are reachable from the internet directly (rows 2 and 4), while private IPs are only reachable within local networks and need NAT for internet access (rows 1 and 3).

Visual Quiz - 3 Questions

Look at the execution_table at step 2. What type of IP is assigned and why?

A No IP assigned because device is offline

B Private IP because device is inside local network

C Public IP because device is outside local network

D Private IP because device needs internet access

💡 Hint

Check the 'Device Location' and 'IP Assigned' columns at step 2 in execution_table.

At which step does a device inside a local network get assigned the IP 10.0.0.7?

A Step 3

B Step 1

C Step 4

D Step 5

💡 Hint

Look at the 'IP Assigned' column for private IPs in execution_table.

If a device inside a local network was assigned a public IP directly, how would the execution_table change?

A The device would not get any IP assigned

B Private IP would be replaced by a public IP in that step

C No change, private IPs are always assigned

D The device would get two IPs assigned

💡 Hint

Consider the 'IP Assigned' and 'Device Location' columns and how they relate in execution_table.

Concept Snapshot

Private IPs are used inside local networks and are not reachable from the internet.
Public IPs are unique on the internet and allow direct access.
Devices with private IPs use NAT on routers to access the internet.
Private IP ranges include 192.168.x.x, 10.x.x.x, and 172.16.x.x to 172.31.x.x.
Public IPs are assigned by internet providers and are globally unique.

Full Transcript

This visual execution trace shows how devices get assigned either private or public IP addresses based on their location. Devices inside local networks receive private IPs like 192.168.1.5 or 10.0.0.7, which are used only within that network. Devices outside local networks get public IPs such as 203.0.113.10, which are unique on the internet. Private IP devices access the internet through a router using NAT, which translates their private IP to the router's public IP. The execution table tracks each step of IP assignment and network access, clarifying common confusions about why private IPs are used and how internet access works for local devices.

Practice

1. Which of the following IP address ranges is reserved for private networks?

easy

A. 192.168.0.0 to 192.168.255.255

B. 8.8.8.8 to 8.8.8.255

C. 172.32.0.0 to 172.47.255.255

D. 1.1.1.1 to 1.1.1.255

Solution

1. Step 1: Identify private IP ranges

   Private IP addresses include 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 ranges.

2. Step 2: Match given options to private ranges

   A and B are public ranges. C (172.32.0.0 to 172.47.255.255) is outside the private 172.16.0.0/12 range. D matches the private 192.168.0.0/16 range.

3. Final Answer:

   192.168.0.0 to 192.168.255.255 -> Option A

4. Quick Check:

   Private IP range = 192.168.x.x [OK]

Hint: Private IPs start with 10., 172.16-31., or 192.168. [OK]

Common Mistakes:

• Confusing public IPs like 8.8.8.8 as private
• Not knowing the specific private IP ranges
• Assuming all IPs starting with 1 or 8 are private

2. Which of the following is a valid public IP address?

easy

A. 192.168.1.1

B. 8.8.8.8

C. 172.20.10.5

D. 10.0.0.1

Solution

1. Step 1: Identify private IP addresses

   10.0.0.1, 192.168.1.1, and 172.20.10.5 are all within private IP ranges.

2. Step 2: Check which IP is outside private ranges

   8.8.8.8 is a public IP address used by Google DNS servers.

3. Final Answer:

   8.8.8.8 -> Option B

4. Quick Check:

   Public IP example = 8.8.8.8 [OK]

Hint: Public IPs are not in private ranges like 10., 172.16-31., 192.168. [OK]

Common Mistakes:

• Choosing private IPs as public by mistake
• Not recognizing common public IPs like 8.8.8.8
• Assuming all IPs starting with low numbers are private

3. Consider a device with IP address 192.168.1.10. What type of IP address is this?

medium

A. Loopback IP address

B. Public IP address

C. Broadcast IP address

D. Private IP address

Solution

1. Step 1: Identify the IP address range

   192.168.1.10 falls within the 192.168.0.0 to 192.168.255.255 range, which is reserved for private networks.

2. Step 2: Understand IP address types

   Private IPs are used inside local networks and are not routable on the internet. This matches the given IP.

3. Final Answer:

   Private IP address -> Option D

4. Quick Check:

   192.168.x.x = Private IP [OK]

Hint: 192.168.x.x always means private IP [OK]

Common Mistakes:

• Confusing private IP with public IP
• Thinking 192.168.x.x is loopback or broadcast
• Not knowing IP address classifications

4. A network administrator assigns the IP address 172.32.0.1 to a device. What is the issue with this assignment?

medium

A. 172.32.0.1 is outside the private IP range and should be public

B. 172.32.0.1 is a loopback address and cannot be assigned to devices

C. 172.32.0.1 is a private IP address and cannot be used publicly

D. 172.32.0.1 is a broadcast address and cannot be assigned

Solution

1. Step 1: Check the private IP range for 172.x.x.x

   The private range for 172 is from 172.16.0.0 to 172.31.255.255. The IP 172.32.0.1 is just outside this range.

2. Step 2: Understand implications of IP outside private range

   Since 172.32.0.1 is outside the private range, it is considered a public IP and must be assigned carefully to avoid conflicts.

3. Final Answer:

   172.32.0.1 is outside the private IP range and should be public -> Option A

4. Quick Check:

   172.16-31.x.x = Private, 172.32.x.x = Public [OK]

Hint: 172.16 to 172.31 is private; 172.32 is public [OK]

Common Mistakes:

• Assuming all 172.x.x.x are private
• Confusing broadcast or loopback with this IP
• Not checking exact private IP range boundaries

5. You want to set up a home network that connects multiple devices but does not expose them directly to the internet. Which IP address type should you use and why?

hard

A. Public IP addresses, because they allow direct internet access

B. Broadcast IP addresses, because they send data to all devices

C. Private IP addresses, because they keep devices hidden from the internet

D. Loopback IP addresses, because they test network connections

Solution

1. Step 1: Understand the purpose of private IP addresses

   Private IPs are used inside local networks to allow devices to communicate without being directly visible on the internet.

2. Step 2: Match network setup needs to IP type

   For a home network that should not expose devices directly, private IP addresses are ideal to provide local connectivity and security.

3. Final Answer:

   Private IP addresses, because they keep devices hidden from the internet -> Option C

4. Quick Check:

   Home networks use private IPs for local security [OK]

Hint: Use private IPs for local networks hidden from internet [OK]

Common Mistakes:

• Choosing public IPs and risking exposure
• Confusing broadcast or loopback IPs with usable device IPs
• Not understanding network security basics