libvirt: Integrate passt --hostname --fqdn options
Git Pull Request
Test Plan
Description
e-tool
May 19, 2026 at 5:56 PMSince the problem described in this issue should be resolved in a recent advisory, it has been closed. For information on the advisory (Moderate: libvirt security update), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHSA-2026:18326
Enrique Llorente Pastora
April 13, 2026 at 5:18 PM@Daniel Vozenilek The description looks technically accurate and covers the integration of hostname and FQDN options in the passt backend for libvirt.
One minor note: as observed in Han Han's verification, the DHCP FQDN option is missing the trailing dot, which appears to be a passt bug (already reported upstream). Otherwise, the documentation is correct.
Daniel Vozenilek
April 29, 2026 at 6:09 PMThank you for the review!
Daniel Vozenilek
April 12, 2026 at 9:19 PM(edited)@Enrique Llorente Pastora, I've prepared an RN draft for this feature. Could you take a look and let me know if the description is technically accurate?
RN draft:
Configure hostname and FQDN options in `libvirt` XML configuration:: The `libvirt` virtualization API supports setting hostname and Fully Qualified Domain Name (FQDN) options for virtual machines on network interfaces that use the `passt` backend. This feature integrates `passt` DHCP and DHCPv6 capabilities to simplify network identity assignment. As a result, you can configure hostname and FQDN directly in the domain XML. For example: + [source,xml] ---- <backend type='passt' hostname='vm1' fqdn='vm1.kubevirt.org'/> ---- + Both attributes are optional. + link:https://issues.redhat.com/browse/RHEL-79806[RHEL-79806]
Han Han
October 29, 2025 at 7:19 PM(edited)Verified on:
libvirt-11.8.0-1.el10.x86_64
qemu-kvm-10.1.54-2.el10.wrb251008.x86_64
passt-0^20250512.g8ec1341-2.el10.x86_64
Steps:Test on libvirt as https://redhat.atlassian.net/browse/RHEL-120907?focusedId=28239687&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-28239687
Check the dhcp options in guest:
Start the domain with hostname and fqdn: <backend type="passt" hostname="vm3" fqdn="vm1.kubevirt.org."/>
Monitor the dhcp options in guest by tshark:
tshark -i eno1 -f "udp port 67 or 68 or 546 or 547" -T ek -e dhcp.fqdn.name -e dhcpv6.client_domain -e dhcp.option.hostnameIn another terminal, restart the nm connection of passt:
nmcli connection down Wired\ connection\ 1 && nmcli connection up Wired\ connection\ 1Get the dhcp options from tshark:
{"timestamp":"1761732400078","layers":{"dhcp_fqdn_name":["vm1.kubevirt.org"],"dhcp_option_hostname":["vm3"]}} ... {"timestamp":"1761732401595","layers":{"dhcpv6_client_domain":["vm1.kubevirt.org."]}}**
The value of option dhcp_fqdn_name is missing the trailing dot. I think it is a passt bug. Report it at https://bugs.passt.top/show_bug.cgi?id=170 . The others work well.
Reference for DHCP options:
DHCP options: https://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml
DHCPv6 options: https://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-parameters.xhtml
Wireshark filters for DHCP options: https://www.wireshark.org/docs/dfref/d/dhcp.html
Wireshark filter for DHCPv6 options: https://www.wireshark.org/docs/dfref/d/dhcpv6.html
Han Han
October 14, 2025 at 2:21 PM
Details
NormalPagerDuty
The passt project now support the DHCP and DHCPv6 options to pass the hostname (DHCPv6) and fqdn, the libvirt project should integrate those into the domain xml part that configure passt.
A possible syntax would be:
<backend type='passt' hostname='vm1' fqdn='vm1.kubevirt.org'/>Both options are optional.