------- Comment From [email protected] 2026-07-01 02:13 EDT------- **[Triage Analysis ? AI Assistant (bzr-triage-new skill)]**
**Root cause:** The second KVM guest interface (vnet1/enp0s8) does not get a DHCP lease from nattest3/virbr3 because the guest's **netplan configuration only enumerates one interface**. cloud-init (which writes `/etc/netplan/50-cloud-init.yaml`) only generates a DHCP stanza for the interface it discovers at first boot ? the first virtio NIC (enp0s1). The second virtio NIC is not added to netplan, so no DHCP request is sent for it. **Evidence:** - Both Ubuntu 26.04 (kernel 6.18.0-8) and Ubuntu 25.04 (6.14.0-37) netplan configs contain **only one interface** ? confirming this is a cloud-init/netplan issue, not kernel-version-specific - `virsh net-dhcp-leases nattest3` is empty across all tests ? the DHCP server never received a request on virbr3 - `dhclient` on the second interface works manually ? confirms the bridge/dnsmasq are correctly configured; the problem is the guest never issues a DHCP request for the second NIC at boot - On kernel 7.0.0-22 both interfaces DO get IPs at boot (comment #13), but the netplan yaml still only has enp0s1 ? this strongly suggests a recent **cloud-init or netplan fix** started enumerating/configuring additional unconfigured interfaces using a fallback mechanism (netplan's "unmanaged" fallback or a cloud-init multi-NIC enumeration fix) **Component:** This is a **cloud-init / netplan** bug, not a kernel or KVM/libvirt bug. The kernel fix observation is a side-effect ? the fix is in userspace packages updated alongside the newer kernel. **Non-bug scenarios ruled out:** - libvirt/dnsmasq are correctly configured (both DHCP ranges are defined, nattest3 is active) - Duplicate bridge MAC address was tested and ruled out (comment #3) - Reproducible on both Ubuntu 25.04 and 26.04 guests ? not release-specific **Upstream status:** Mirrored to Canonical Launchpad as bug #44986 (core-network). Fix appears present in Ubuntu packages shipping with kernel 7.0.0-22-generic. Backport to earlier kernels (6.14/6.18) needed. **Recommended actions:** 1. Follow up on LP #44986 to identify the specific cloud-init or netplan commit that introduced the fix 2. Confirm the fix is backported to Ubuntu 25.04 (Plucky) and 26.04 LTS packages independent of kernel version 3. Upgrade severity to **major** ? a VM with two NICs silently losing one at boot has broad impact for multi-homed guest deployments 4. Assignee: request Canonical to identify the fixing package version so the bug can be closed with a specific fix reference -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2140533 Title: [Ubuntu 26.04] DHCP not working on second bridge for guest network To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-power-systems/+bug/2140533/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
