Azure Virtual Network now supports reverse DNS lookup (PTR DNS queries) for virtual machine IP addresses by default. Use this to quickly look up name of the VM from its IP address. Previously, using DNS queries to look up the fully qualified domain name (FQDN) for a virtual machine from its IP address would result in an NXDOMAIN response. Now, instead of getting an NXDOMAIN, you’ll receive valid FQDN of the virtual machine to which the IP address belongs.
For additional details please read the documentation.