We have a web application on the Hyper V Guest attempting to use SMTP services on the Hyper V Host. We're setting up our first Hyper-V server with a guest OS W2008. The Hosting ISP account has 4 IPs set as perferred IPs. So, we're using an internal network adaptor for the VM which is shared to the NIC adaptor and have assigned guest OS network a single perferred IP. Guest Machine : Setup a network adapter using an External IP - 62.34.123.98, Subnet mask - 255.255.255.0 and the Default gateway 62.34.123.1 On the Host Computer: Using the Virtual Network manager created an Internal Connection Type called “My internal Connection to the Virtual Machine” Changed the Network Adapters properties of the “My internal Connection to the Virtual Machine” connection; Sharing Tab – selected the “Allow other networks users to connect through this computer’s internet connection”Networking Tab – selected the “Internet Protocal Version 4(TCP/IPv4) properties. Under ‘General’ Selected 'Use the following IP addresses' entered an External IP - 62.34.123.98 , Subnet mask - 255.255.255.0, and the Default gateway 'blank' Clicked ‘Ok’ Seemed to work well, the Webserver is resolving to the internet and FTP Server works. Unfortunately, we're unable to communicate between the Host and Guest for any SMTP requests. We've tried to debug using telnet without success. Using Telnet from an external computer, we can resolve the IIS,SMTP and FTP to the Host and the Guest OS. Additionally we are able to resolve those from the respective host or guest using Telnet. But, When we are unsuccessful using telnet to resolve to the Host from the Guest for those same services.

Hi ErgoDave,Why don't you use the Internal Network adapter? Since Virtual machines connected to this type of network can communicate among themselves and the management OS. There is no connectivity with the physical network. I think you may need to take a look at the following article:http://www.microsoft.com/downloads/details.aspx?FamilyID=3FAC6D40-D6B5-4658-BC54-62B925ED7EEA&displaylang=en&displaylang=en

Thanks for the reply and the link to the suggested reading. The Internal Network Adapter is being used. In the earlier description this adapter is called "My internal connection to the Virtual Machine" We did choose the internal adapter with a shared based on the circumstances. We have static ip and RDP to this server and as noted in the 'Understanding Networking with Hyper-V'"When applying changes for an external network switch, network connectivity may be lost temporarily; this will disrupt network operations in progress. If the physical network adapter has static settings, these settings will be overwritten and will need to be reapplied to the newly created virtual NIC in the management OS. This is important when working on the configuration via Remote Desktop." How can we create an external network adapter with those circumstances?

I do not like including the host in a setup like this. I find it best to ignore the host OS and regard the host as simply the "engine" to power the vms. Instead of using an internal virtual network use a private virtual network (with no connection to the host). Do your testing from another machine. You can RDP directly to each vm. Forget about Hyper-V and regard each vm as just another machine in your network. The message you quote only effects you when you actually create the virtual network. If you are sitting at the console of the server you may not even notice. You will certainly notice if if you are connected to the Hyper-V server by RDP! Your connection will drop and you will have to reconnect to the "new" NIC.Bill

Hi, I just want to check if the information provided was helpful. If there is any update on this issue, please feel free to let us know. We are looking forward to your reply.

I have a VERY similar problem going on. In my case, I have service running in several different VMs across 32 Hyper-V hosts which need to send SMTP messages through an SMTP relay residing on a physical host not running Hyper-V. Using a Telnet client from any Hyper-V host, I can susccessfully connect to the SMTP relay. However, using th same methodology, I CANNOT connect to the SMTP relay from any virtual machine. I CAN ping the SMTP relay and connect to web services running on that same host from any virtual machine. Any thoughts or suggestions would be welcome!