Maximum VMs in Azure Subnet /25
You have an Azure virtual network named VNet1 that contains the following settings: • IPv4 address space: 172.16.10.0/24 • Subnet name: Subnet1 • Subnet address range: 172.16.10.0/25 What is the maximum number of virtual machines that can connect to Subnet1?
Community Votes
100% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
The core concept is subtracting reserved addresses from the total host capacity, but candidates often forget Azure-specific reservations like the Service Tag or Gateway.
This question tests the calculation of usable IP addresses in a subnet to determine the maximum number of virtual machines. The correct answer is C (123) based on the exam's specific assumptions about reserved IPs.
Candidates often select D (128) by calculating 2^7 without subtracting any reserved addresses, or B (25) by misinterpreting the CIDR notation.
Community Discussion (3 comments)
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Expert Analysis
Why the Answer Is Correct
In Azure, a /25 subnet provides 2^(32-25) = 2^7 = 128 total IP addresses. However, not all are available for VMs. Microsoft reserves the first 4 IPs (e.g.,.0,.1,.2,.3) and typically the last IP (.254) for gateway purposes. This leaves 128 - 5 = 123 usable addresses for VMs. While standard networking might suggest fewer reservations, Azure's specific implementation often accounts for these five non-assignable addresses in certification contexts.Why the Other Options Are Wrong
Option A (24) and B (25) are too low, likely resulting from miscalculating the host bits or confusing /25 with /26 or other subnets. Option D (128) represents the total address count without subtracting any reserved IPs, which is incorrect because Azure does not allow assigning the network broadcast or gateway IPs to VMs. Option E (251) corresponds to a /24 subnet (256 - 5), which does not match the /25 configuration in the question.Community Comment Notes
Community comments generally align with the calculation of 128 total addresses minus reserved ones. One user noted that 'A /25 CIDR notation means... 7 bits are used to define individual hosts... 2^7 = 128 total addresses. However, 5 addresses' are reserved, leading to 123. Another user mentioned '125 free IP address numbers' but failed to account for all Azure-specific reservations, highlighting the difficulty in knowing exact reservation counts.Exam Strategy
Memorize the formula for usable IPs: Total Addresses - Reserved Addresses. For Azure, assume at least 5 reserved IPs per subnet (first 4 + last 1 for gateway). Always check the CIDR mask to calculate total hosts first using 2^n.
Frequently Asked Questions
Why is the answer 123 and not 128?
Azure reserves the first 4 IPs and the last IP (gateway) in every subnet, leaving 123 usable IPs out of 128 total.
How many bits are for hosts in a /25 subnet?
A /25 subnet uses 7 bits for hosts (32-25), resulting in 2^7 = 128 total addresses.
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