Allocation Of Host Addresses

Question

Hello, i am doing a school project and have a question. I created two subnets and i am trying to figure out how the bits are allocated. I use a formula (2^8)-2 and come up with an answer of 254 IPv4 host addresses, yet displayed are 251. Was wondering if anyone had answers as to where the 3 addresses are allocated.

Answer 1

Hi Gary,

Besides IPs reserved for network and broadcast, Azure also reserves an IP for default gateway and two IP addresses for DNS in each subnet. See excerpt from Azure Virtual Network FAQ below:

Are there any restrictions on using IP addresses within these subnets?

Yes. Azure reserves the first four addresses and the last address, for a total of five IP addresses within each subnet. For example, the IP address range of 192.168.1.0/24 has the following reserved addresses:

• 192.168.1.0: Network address.
• 192.168.1.1: Reserved by Azure for the default gateway.
• 192.168.1.2, 192.168.1.3: Reserved by Azure to map the Azure DNS IP addresses to the virtual network space.
• 192.168.1.255: Network broadcast address.

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Thanks.

-TP