Friday, September 11, 2009

VPC:s and Shared Networking

I used VPC:s all the time and we often clone VPC:s to all project members. However, there is a very tricky part of VPC:s and Microsoft CRM environments and this concerns SID:s.

As you might know, each windows machine has a SID, which is supposed to be a unique identifier for the machine. Exactly when it is used, I am not certain of but I know that you can get into a whole lot of strange trouble if you have two computers with the same SID on the same LAN.

It can easily be changed on any normal windows machine or server with forinstance the tool newsid. However, there is one type of machine that you cannot change SID on and that is a domain controller.

To ease the managing of normal VPC:s it is usually best to create VPC:s that contain everything in one. That is, Windows server, Domain controller, SQL Server, Reporting Services, Visual Studio 2008 and, of course, CRM.

So, we have several VPC:s that have the same SID and we have people sitting next to eachother running them at the same time. The only network setting that can be selected, to still conect to the internet in the VPC is hence, Shared Networking.

This setting is actually a small local network in it self with a NAT (Network Address Translation)/ DHCP server/switch in the VPC host program.

I noticed a problem today when I started up a VPC and noted that I had forgotten to connect the network cable. After I had inserted the network cable and my host PC had full access, I still had problems getting an IP address and a propper connection to the internet from my VPC.

After some fiddeling with trying to run ipconfig /release, ipconfig /renew and sleeping the VPC, I finally shut down the host program and opened the VPC again after which I ran ipconfig /renew, finally it worked.

My interpretation of this is that the NAT/DHCP server need to have a working network connection in the VPC to intitialize properly. Since I didn't, it just miss started and my VPC:s never got any proper IP:s. The only possible way of restarting it is to restart the VPC host program. After it has been started, you just have to run ipconfig /renew to get a new IP from the VPC DHCP/NAT server.

Gustaf Westerlund
Microsoft Dynamics CRM Architect


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