Both Windows Azure Pack and Windows Azure use IPSec S2S VPN to connect on-premise environment to the virutal network in Cloud. Now the question is is that possible connect to those virtual networks together.
I decided to give it a try and first created a virutal networks in both Windows Azure (I use Mooncake in this case.) and Windwos Azure Pack (My own lab environment).
Then I created a S2S VPN on LARRYZHHNV1 (which is in Windows Azure Pack environment).
Since we didn't create VPN Gateway for Windows Azure virtual network yet, I don't have the VPN Gateway address. So I use a fake IP here. Same for the shared key. We may configure the remove VPN gateway address and pre-shared key later.
Next step, I created a gateway for my virtual network on Windows Azure. Now I have the gateway IP and key. I use that infomration update the S2S VPN configuration in WIndows Azure Pack. After that you could see the status of the S2S VPN on Azure is connected.
On WSG we may use cmdlet "Get-VpnS2SInterface" to check the VPN connection status. It also shows connected.
In my case, I need to disconnect and VPN and reconnect it again. Now the VMs in two cloud can talk to each other.