Windows DHCP server problem on Xen VM hosts

Posted by Christian Ashby on May 6, 2010

If your XenServer hosted Windows DHCP server(s) are running on the same physical host as linux DHCP clients, then they will not receive a DHCP address.

To work around this problem, turn off checksum offloading on the network adapter. To do this, follow these steps:

  • Click Start, click Run, type regedit, and then click OK.
  • Locate and then click the following registry key: 
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
  • In the right pane, make sure that the DisableTaskOffload registry entry exists. If this entry does not exist, follow these steps to add the entry:
    • On the Edit menu, point to New, and then click DWORD value.
    • Type DisableTaskOffload, and then press ENTER.
    • Click DisableTaskOffload.
    • On the Edit menu, click Modify.
    • Type 1 in the Value data box, and then press ENTER.
    • Exit Registry Editor.

Note that this doesn’t effect Open-Source Xen as it is specifically related to the XenServer-supplied PV drivers.

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Remote desktop ‘Exceeded the number of connections’

Posted by Christian Ashby on May 4, 2010

You can optionally connect to the ‘console’ which is a screen 0 (by default screens 1 and 2 are the screens you connect to with a remote desktop client). This option is not in the Windows UI, you need to use the following command from Start->Run:

mstsc -v:{machine address} /f -console

Windows Vista / Windows 7 use the syntax /admin rather than -console.

If you use a mac, you can put /console at the end of the machine name in the machine box.

If you use linux and rdesktop then add -0 to the rdesktop command line.

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