Azure: Restricted Subnet IPs
When planning for Azure network, I did not know there are IP addresses that are restricted, or reserved, and cannot be used:
x.x.x.0
: This is the network address and is used to identify the subnet itself. It cannot be assigned to any individual device.x.x.x.1
: Azure reserves this address for the default gateway of the subnet, which serves as an access point to other networks.x.x.x.2
,x.x.x.3
: These addresses are reserved to map the Azure DNS IPs to the VNet space, ensuring that DNS services are properly routed within the network.x.x.x.255
: Known as the network broadcast address, it is used to communicate with all devices within the subnet simultaneously.
Understanding these restrictions is vital when designing your network to avoid potential connectivity issues. For example, if you create a subnet with a /24
address range, you might expect to have 256 IP addresses at your disposal. However, after accounting for the five reserved addresses, the actual number of usable IP addresses is reduced to 251.
This distinction between theoretical and actual IP address availability is a key consideration in network planning to ensure sufficient address space for all your devices and services. It’s also important to remember that Azure may reserve additional addresses for its own management purposes, which can vary depending on the services you deploy within your VNet.
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