Libvirt is using its autoport setting to automatically allocate ports within a range starting at 5900.

Example excerpt from an XML configuration for a VM:

<graphics type='spice' port='6000' autoport='yes' listen='127.0.0.1' keymap='en-gb'>
    <listen type='address' address='127.0.0.1'/>
</graphics>

Currently, there are free ports at various points within the range 5900 to 5999.

However, newly booted VMs are picking up ports from 6000 on. I need for it to reuse the available ports in the 59xx range.

Is this possible? If so, how do I do this?

The problem arose because VMs are being accessed via websockets, and it tried to use 6000 which is a reserved port for X11. A solution that explains how to blacklist ports from being picked up by autport would also be sufficient.