CIDR notation in Computer Networks - Step-by-Step Execution

Concept Flow - CIDR notation

Start with IP address

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Add '/' and prefix length

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Calculate subnet mask from prefix

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Determine network and host parts

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Use for routing and IP allocation

CIDR notation shows an IP address with a suffix that tells how many bits are for the network part, helping to divide IP addresses efficiently.

Execution Sample

Computer Networks

192.168.1.0/24

# /24 means first 24 bits are network
# subnet mask: 255.255.255.0
# host bits: 8 (32-24)
# total addresses: 256 (254 usable)

This shows an IP address with a /24 prefix, meaning the first 24 bits are network bits, leaving 8 bits for hosts.

Analysis Table

Step	Action	Value/Calculation	Result
1	Start with IP address	192.168.1.0	192.168.1.0
2	Add prefix length	/24	192.168.1.0/24
3	Calculate subnet mask	24 bits network	255.255.255.0
4	Determine network part	First 24 bits fixed	192.168.1.0
5	Determine host part	32 - 24 = 8 bits	256 addresses total
6	Calculate usable hosts	256 - 2 (network & broadcast)	254 usable IPs
7	Use in routing	Route traffic to 192.168.1.0/24	Network identified
8	End	Prefix length defines subnet size	Execution complete

💡 Prefix length fully defines network and host division, stopping further calculation.

State Tracker

Variable	Start	After Step 3	After Step 5	Final
IP Address	192.168.1.0	192.168.1.0	192.168.1.0	192.168.1.0
Prefix Length	N/A	24	24	24
Subnet Mask	N/A	255.255.255.0	255.255.255.0	255.255.255.0
Host Bits	N/A	N/A	8	8
Total Addresses	N/A	N/A	256	256
Usable Hosts	N/A	N/A	N/A	254

Key Insights - 3 Insights

Why does /24 mean 255.255.255.0 as subnet mask?

Because /24 means the first 24 bits are network bits, which in decimal form is 255.255.255.0 as shown in execution_table step 3.

Why subtract 2 from total addresses to get usable hosts?

Two addresses are reserved: one for the network itself and one for broadcast, so usable hosts are total minus 2, as shown in step 6.

What does the prefix length tell us about the IP address?

It tells how many bits are fixed for the network part, separating network and host bits, as seen in steps 3 and 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the subnet mask calculated at step 3?

A 255.0.0.0

B 255.255.0.0

C 255.255.255.0

D 255.255.255.255

💡 Hint

Check the 'Result' column in step 3 of the execution_table.

At which step do we find out how many host bits are available?

A Step 5

B Step 2

C Step 4

D Step 6

💡 Hint

Look for where 'Host Bits' or '32 - prefix' is calculated in execution_table.

If the prefix length changed from /24 to /26, how would the total addresses change?

A Decrease to 128

B Decrease to 64

C Increase to 512

D Stay the same at 256

💡 Hint

Recall total addresses = 2^(32 - prefix length). Check variable_tracker for prefix length effect.

Concept Snapshot

CIDR notation shows an IP address with a slash and number (e.g., /24).
The number is how many bits are for the network part.
Subnet mask is derived from this prefix length.
It divides IPs into network and host parts.
Used to allocate IPs efficiently and route traffic.

Full Transcript

CIDR notation is a way to write IP addresses that includes how many bits are used for the network part. For example, 192.168.1.0/24 means the first 24 bits are network bits. This corresponds to a subnet mask of 255.255.255.0. The remaining bits are for hosts, so with 8 host bits, there are 256 total addresses. Two addresses are reserved for network and broadcast, leaving 254 usable IPs. This notation helps computers know which part of the address is the network and which part is the device, making routing and IP allocation more efficient.