Up until August 1st if you had 2 vNets in the same Azure region (USWest for example) you needed to create a site to site VPN between them in order for the VMs within each vNet to be able to see each other. I’m happy to report that this is no longer the case (it is still the default configuration). On August 1st, 2016 Microsoft released a new version of the Azure portal which allows you to enable vNet peering between vNets within an account.
Now this feature is in public preview (aka. Beta) so you have to turn it on, which is done through Azure PowerShell. Thankfully it uses the Register-AzureRmProviderFeature cmdlet so you don’t need to have the newest Azure PowerShell installed, just something fairly recent (I have 1.0.7 installed). To enable the feature just request to be included in the beta like so (don’t forget to login with add-AzureRmAccount and then select-AzureRmSubscription).
Read the whole thing for details on how to enroll in this feature and how to set it up.