Thank you all very much,for replying.
Can I ask the following questions :
1. are the fw rules added by libvirtd, hardcoded in libvirtd source code or editable ?
2. can a sys admin enable ou disable these rules inclusion (ie set a paramater somewhere
so that these rules are or are not included in currently running firewall) ?
Given the variety of roles a Linux host can run, having a single set of rules to fit all
these roles is impossible.
Giving sys admins the keys (documentation, examples, ...) to let them tune whatever they
need is enough.