Dom0 mem allocation and domU network issues

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    If your network is disappearing on you or if you would rather have a working Xen setup, in your /boot/grub/grub.conf put this line at the end of the kernle line for your Xen kernel: dom0_mem=768M lowmem_emergency_pool=16M

    It should look like this:

    kernel /xen.gz-3.3.0 dom0_mem=768M lowmem_emergency_pool=16M

    Why you wonder?  Xen will hand all of the system memory over to dom0 if you don't restrict it at boot.  Then, as the virtuals fire up, Xen will remove memory from dom0 and pass it to the starting domU.  This is not a very fun thing for it to do and it results in the domU losing access to things like the network driver.  So, if you find that when your virtuals are starting suddenly they lose their network connectivity or if you seem to be running just fine and then your networking on your domU's goes away, this is quite likely your issue.

    Here's what your syslog has to say to you when you're having this issue:

    kernel: xen_net: Memory squeeze in netback driver.

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