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Getting a Windows RRAS VPN server working on XenServer

A quick note on this. I was troubleshooting a problem today of a newly setup Windows RRAS PPTP VPN server was not working. Or rather it was kind of working. You could connect and authenticate, but when it came time to passing traffic you could only ping the RRAS server itself. Which is a bit troublesome if you are wanting to access anything else on the network such as your file server, your domain controller, your Exchange server and so forth.

Capturing traffic via Wireshark did show that traffic from the VPN client would pass beyond the RRAS server and a reply would be sent. It just never makes it back to the client from the RRAS. Some quick queries to Google turned up little beyond more familiar problems of incorrectly configured multihomed RRAS servers. Which proved not to be the case here. It turned out that TCP offloading was rearing its ugly head again. After switching that off in the properties for the NIC in question traffic immediately started passing back and forth properly. This made for happy clients. So the moral of the story is probably that you should always suspect offloading no matter how fixed it is claimed to be. Or perhaps to use Intel NICs instead of Broadcom, but that remains as something that I will have to test out later if I get the opportunity.


USB Drive Disappears from Removable Storage on XenServer after a Reboot

Quick fix for an annoying problem I ran across where the removable storage no longer shows the attached usb drives after a reboot under XenServer 5.6. Pop open a console window on your XenServer host:

modprobe -r usb_storage … this removes the usb_storage kernel driver

modprobe usb_storage … this reinstalls the usb_storage kernel drives

That should get you your drives back and if you don’t see them then just do a rescan.

xe sr-list | grep -i removable -B 1 … use this to find the UUID of your removable storage SR

xe sr-scan uuid=<uuid of removable storage> … your usb drives should be showing up now ready to be attached to your VM

Addressing P2V 0x7b Issues

The other night I was P2Ving several systems and on one I ran into the issue of it blue screening on boot. It is unfortunate but not too uncommon as usually you need to enable IDE drivers on the system prior to the P2V. Microsoft’s article here works for all versions of XP and Server 2003, though I found I needed to expand the mentioned drivers directly from the cd for the SBS system I was working. That unfortunately did not resolve my 0x7b blue screen the other night. This article turned out to be the key to what I needed. Now the part that neither of these mentions is how to fix the problem if you can’t even boot that VM, so as to avoid having to do another P2V of the system. With Server 2008 this is possible to avoid and it can save you a lot of time, especially if the systems are large.

Server 2008 contained a great feature of being able to mount VHDs which is what we’ll be doing. For the first method you’ll want to mount the VHD to a drive letter and then expand the drivers to the \windows\system32\drivers folder in the VHD. Pull up regedit and select the HKLM key. Go to File->Load Hive and open the system registery from the \windows\system32\config\ and give it an easily identifiable name. You’ll find the registery loaded in HKLM under the name that you gave. Now loading the registery this way you won’t find a CurrentControlSet under the SYSTEM key. CurrentControlSet is just a pointer to ControlSetxxx. To find out which ControlSet number the system is set to boot with look ing SYSTEM\Select. The Current dword contains the number that it is using which in most cases will be 1, so go into that particular ControlSet i.e. for 1 it will be ControlSet001. In there you can manually implement the keys from the first article or the second article. In the case of the problem I ran into I had to set the Group Value of wdf01000 to WdfLoadGroup as it was part of the base group. If you want to learn more about service orders take a look at this article and this article.

Once done with those changes unload the hive and close out of regedit. Dismount the VHD and your virtual machine should be good to go.

Virtualization for Practice

When you start studying for your MCSE or MCITP: EA there does come a point where you have to get some hands on experience with the technology. There are simulations in the exams that you will have to face at some point and if you’re just book smart alone you might not be able to sail through those with ease. Even more importantly when you’re on the job you are going to have to do what your credentials claim you can do. So what’s an easy way to start getting all of that practice right there in the comfort of your very own home? Well for one you can start downloading a trial copy of Windows Server 2008 or of 2003. That will get you the software, but chances are you don’t have too many machines sitting around to use as servers, as well as clients. This is where virtualization comes to the rescue.

Virtualization is what enables you to run a machine, and actually several machines, inside of one physical machine. With these virtual machines you can make up a whole virtual environment of servers and clients purely for your testing and enjoyment purposes. You can even set up several different networks so as to simulate two or more separate sites and/or forests. Virtual machines are also a great way to step towards high availability, but that is for another time as we are just going to talk about them for study purposes right now. So currently there are two easily accessible ways of achieving this virtualization. One way is through the use of a bare metal hypervisor. This will require a separate machine that you will be dedicating purely to virtualization. Another way is through a hosted hypervisor. This typically installs as an application upon your OS of choice and you use at will. For enterprise use a bare metal hypervisor is usually the best solution but for a simple at home lab for study purposes you would probably be best off with a hosted hypervisor. Let’s run through a few popular options we have available.

First and most famous is VMware. You have the options here of VMware Server and VMware Workstation. Server is free but Workstation will cost you. Unless there be a must have feature from Workstation, you should stick with Server. It’s free and it will get your virtual lab going trouble free. There are version available for Windows hosts as well as Linux hosts. The interface is not too difficult to learn and once you have it set up it will stay out of your way. I have read that it is possible to install Hyper-V into VMware but I have not tested it out myself yet. This is something you may wish to keep in mind when planning your MCITP training lab.

Next up is VirtualBox. This virtualization product is relatively new to the scene compared to VMware but it is growing in popularity. This one is also freely available. This is my hosted hypervisor platform of choice in a Linux environment, and it is available for Windows as well. The reason I went with Linux for my host is simple. If you have 4 or more gigabytes of ram then you will want to use a 64-bit operating system. You will also want to make sure that you have hardware extensions such as Intel VTx or AMD-V available AND enabled in the BIOS if you are planning for 64-bit. VirtualBox I have found to be the easiest out of the box experience if you’re using Linux as a host.

Some other options are QEMU and Microsoft VirtualPC. I have not worked with either of these but VirtualPC is another good choice for Windows hosts from what I have read, with no availability for Linux hosts of course.

If you are wanting to delve into bare metal hypervisors then VMware ESX is definitely the platform of choice. VMware has a free edition available named ESXi but it misses a lot of the functionality of the full package. Hyper-V is another option to consider, especially if you are planning on MCITP studies. In the open source arena Xen is another player, with a more commercial flavor being marketed by Citrix.

For my studies I completed them primarily on openSUSE using VirtualBox. There were a few uses of VMware Server and for test machines at previous jobs I used VMware as well. My choice of using Linux for a host was purely because I did not own a 64-bit copy of Windows and was in need of a 64-bit host. I make no recommendation of host but will recommend VirtualBox for your virtualization platform for its simplicity in configuration and use. Either way pick your platform and start practicing!

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