CIDR blocks and IP addressing in AWS - Step-by-Step Execution

Process Flow - CIDR blocks and IP addressing

Start with IP address

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Apply CIDR mask

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Calculate network address

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Calculate range of IPs

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Identify usable IPs

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Assign IPs to devices

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End

This flow shows how an IP address and CIDR mask combine to define a network and usable IP range.

Execution Sample

AWS

IP = 192.168.1.0/29
# Calculate network and usable IPs

This example calculates the network and usable IP addresses for the CIDR block 192.168.1.0/29.

Process Table

Step	Action	Calculation/Condition	Result
1	Start with IP and CIDR	IP=192.168.1.0, Mask=/29	Given IP block
2	Calculate subnet mask	/29 means 29 bits for network	Subnet mask = 255.255.255.248
3	Calculate number of IPs	2^(32-29) = 8	Total IPs = 8
4	Calculate network address	IP & subnet mask	192.168.1.0
5	Calculate broadcast address	Network + total IPs - 1	192.168.1.7
6	Identify usable IPs	Exclude network and broadcast	192.168.1.1 to 192.168.1.6
7	Assign IPs to devices	Use usable IP range	Devices get IPs 192.168.1.1-192.168.1.6
8	End	All usable IPs assigned	Finished

💡 All usable IPs assigned, network and broadcast reserved

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	Final
IP	192.168.1.0/29	192.168.1.0/29	192.168.1.0/29	192.168.1.0	192.168.1.0	192.168.1.0	192.168.1.0
Subnet Mask	N/A	255.255.255.248	255.255.255.248	255.255.255.248	255.255.255.248	255.255.255.248	255.255.255.248
Total IPs	N/A	N/A	8	8	8	8	8
Network Address	N/A	N/A	N/A	192.168.1.0	192.168.1.0	192.168.1.0	192.168.1.0
Broadcast Address	N/A	N/A	N/A	N/A	192.168.1.7	192.168.1.7	192.168.1.7
Usable IP Range	N/A	N/A	N/A	N/A	N/A	192.168.1.1-192.168.1.6	192.168.1.1-192.168.1.6

Key Moments - 3 Insights

Why do we exclude the first and last IP addresses in the range?

The first IP is the network address and the last is the broadcast address, both reserved and not assignable to devices (see execution_table steps 4 and 5).

How do we calculate the total number of IPs from the CIDR mask?

Subtract the CIDR number from 32, then raise 2 to that power (2^(32 - CIDR)). For /29, 2^(32-29) = 8 (see execution_table step 3).

What does the subnet mask 255.255.255.248 mean in binary?

It means the first 29 bits are network bits (ones), and the last 3 bits are host bits (zeros), defining the size of the subnet (see execution_table step 2).

Visual Quiz - 3 Questions

Look at the execution table, what is the broadcast address calculated at step 5?

A 192.168.1.0

B 192.168.1.6

C 192.168.1.7

D 192.168.1.1

💡 Hint

Check the 'Result' column at step 5 in the execution_table.

At which step do we find the number of total IP addresses in the block?

A Step 3

B Step 2

C Step 4

D Step 6

💡 Hint

Look for the calculation of 2^(32 - CIDR) in the execution_table.

If the CIDR was changed to /30, how would the total IPs change in the execution table?

A Total IPs would be 8

B Total IPs would be 4

C Total IPs would be 16

D Total IPs would be 2

💡 Hint

Recall the formula 2^(32 - CIDR) and apply it for /30.

Concept Snapshot

CIDR blocks define IP ranges using a mask.
CIDR /n means n bits for network, rest for hosts.
Total IPs = 2^(32 - n).
First IP = network address (not usable).
Last IP = broadcast address (not usable).
Usable IPs lie between these two.

Full Transcript

CIDR blocks combine an IP address with a mask to define a network range. The mask tells how many bits are for the network part. For example, /29 means 29 bits for network and 3 bits for hosts. We calculate total IPs by 2 raised to the power of (32 minus the mask). The first IP is the network address and the last is the broadcast address; both are reserved and cannot be assigned to devices. Usable IPs are those in between. This process helps assign IPs efficiently in cloud networks.