[Bug 2138794] Re: [Ubuntu26.04] [FW1110] : Guest network is going down, as MAC address mismatches!
Frank Heimes
2138794 at bugs.launchpad.net
Wed Jan 21 10:47:05 UTC 2026
** Package changed: ubiquity (Ubuntu) => ubiquity
** Also affects: ubuntu-power-systems
Importance: Undecided
Status: New
** Changed in: ubuntu-power-systems
Assignee: (unassigned) => Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage)
** Changed in: ubiquity
Assignee: Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage) => (unassigned)
** Changed in: ubuntu-power-systems
Importance: Undecided => Medium
** Project changed: ubiquity => subiquity
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https://bugs.launchpad.net/bugs/2138794
Title:
[Ubuntu26.04] [FW1110] : Guest network is going down, as MAC address
mismatches!
Status in subiquity:
New
Status in The Ubuntu-power-systems project:
New
Bug description:
== Comment: #0 - Anushree Mathur <Anushree.Mathur2 at ibm.com> - 2026-01-19 15:02:17 ==
Host ENV:
OS : ubuntu26.04
kernel : 6.18.0-8-generic
libvirt : libvirtd (libvirt) 11.6.0
qemu : QEMU emulator version 10.1.0 (Debian 1:10.1.0+ds-5ubuntu4)
Guest ENV:
OS : Ubuntu26.04
kernel : 6.18.0-8-generic
When I installed the guest I can see that the network interface is up but if I bringup the guest after destroying and undefying the guest as the MAC address will be changed for the network interface, now the guest is not getting network up. After some debugging I saw that in the netplan yaml file there is a specific tag "match" i.e for the mac address match. Now whenever the guest bringup is happening the MAC address defined at the time of guest installation is getting mismatched and the network bringup is failing.
Steps to reproduce:
1) Install the 26.04 guest!
2) Check in the guest if the network is up
2: enp0s1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 52:54:00:54:10:8b brd ff:ff:ff:ff:ff:ff
altname enx52540054108b
inet 192.168.122.122/24 metric 100 brd 192.168.122.255 scope global dynamic enp0s1
valid_lft 3322sec preferred_lft 3322sec
inet6 fe80::5054:ff:fe54:108b/64 scope link proto kernel_ll
valid_lft forever preferred_lft forever
3) Check the netplan yaml file
# This is the network config written by 'subiquity'
network:
ethernets:
enp0s1:
dhcp4: true
dhcp6: true
match:
macaddress: 52:54:00:54:10:8b
set-name: enp0s1
version: 2
4) Destroyed and undefined the guest.
5) Bringup the guest again with virt-install, now MAC address will be
randomly given.
6) virsh start network_anu --console
7) sudo ip a
2: enp0s1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
link/ether 52:54:00:0b:d4:fb brd ff:ff:ff:ff:ff:ff
altname enx5254000bd4fb
Now the network will be down.
8) Remove the "match" tag from the netplan and then re apply the
netplan rules. Need to remove the set-name as it also require "match"
tag.
New netplan yaml file is
network:
ethernets:
enp0s1:
dhcp4: true
dhcp6: true
version: 2
9) Now the network is getting brought up.
2: enp0s1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 52:54:00:0b:d4:fb brd ff:ff:ff:ff:ff:ff
altname enx5254000bd4fb
inet 192.168.122.122/24 metric 100 brd 192.168.122.255 scope global dynamic enp0s1
valid_lft 3597sec preferred_lft 3597sec
inet6 fe80::5054:ff:fe0b:d4fb/64 scope link proto kernel_ll
valid_lft forever preferred_lft forever
From the KVM perspective this will be a thing to consider as MAC address will be assigned randomly. I would really like to have more thoughts and a better solution around this as this is the temporary solution I have found until now.
Thanks!
== Comment: #1 - Anushree Mathur <Anushree.Mathur2 at ibm.com> - 2026-01-20 00:53:11 ==
I tried cloning the guest with virt-clone, the cloned guest also doesn't have network up!
Steps I tried:
1) Install ubuntu26.04 guest freshly.
2) Check if the network is there :
2: enp0s1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 52:54:00:6b:81:26 brd ff:ff:ff:ff:ff:ff
altname enx5254006b8126
inet 192.168.122.38/24 metric 100 brd 192.168.122.255 scope global dynamic enp0s1
valid_lft 3581sec preferred_lft 3581sec
inet6 fe80::5054:ff:fe6b:8126/64 scope link proto kernel_ll
valid_lft forever preferred_lft forever
3) Didn't change anything in the netplan rule kept it as it is.
# This is the network config written by 'subiquity'
network:
ethernets:
enp0s1:
dhcp4: true
dhcp6: true
match:
macaddress: 52:54:00:6b:81:26
set-name: enp0s1
version: 2
4) Destroyed the guest.
5) Cloned the guest : virt-clone --original network_check --auto-clone
Allocating 'ubuntu_anu_check-clone.qcow2' | 10 GB 00:00:01
Clone 'network_check-clone' created successfully.
6) Start the cloned guest
7) Check for the network:
2: enp0s1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
link/ether 52:54:00:42:e4:89 brd ff:ff:ff:ff:ff:ff
altname enx52540042e489
Guest doesn't have network up. Cloned guest also doesn't have the
network up. We tested all this in Ubuntu24.04 Ubuntu25.04 also but
this was not the case there.
== Comment: #2 - Raman Singh <Raman.Singh5 at ibm.com> - 2026-01-20 01:21:36 ==
(In reply to comment #1)
> I tried cloning the guest with virt-clone, the cloned guest also doesn't
> have network up!
>
> Steps I tried:
>
> 1) Install ubuntu26.04 guest freshly.
> 2) Check if the network is there :
>
> 2: enp0s1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state
> UP group default qlen 1000
> link/ether 52:54:00:6b:81:26 brd ff:ff:ff:ff:ff:ff
> altname enx5254006b8126
> inet 192.168.122.38/24 metric 100 brd 192.168.122.255 scope global
> dynamic enp0s1
> valid_lft 3581sec preferred_lft 3581sec
> inet6 fe80::5054:ff:fe6b:8126/64 scope link proto kernel_ll
> valid_lft forever preferred_lft forever
>
> 3) Didn't change anything in the netplan rule kept it as it is.
>
>
> # This is the network config written by 'subiquity'
> network:
> ethernets:
> enp0s1:
> dhcp4: true
> dhcp6: true
> match:
> macaddress: 52:54:00:6b:81:26
> set-name: enp0s1
> version: 2
>
> 4) Destroyed the guest.
> 5) Cloned the guest : virt-clone --original network_check --auto-clone
> Allocating 'ubuntu_anu_check-clone.qcow2'
> | 10 GB 00:00:01
>
> Clone 'network_check-clone' created successfully.
>
> 6) Start the cloned guest
> 7) Check for the network:
>
> 2: enp0s1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group
> default qlen 1000
> link/ether 52:54:00:42:e4:89 brd ff:ff:ff:ff:ff:ff
> altname enx52540042e489
>
> Guest doesn't have network up. Cloned guest also doesn't have the network
> up. We tested all this in Ubuntu24.04 Ubuntu25.04 also but this was not the
> case there.
Could you please attach the network config written by 'subiquity' for
Ubuntu24.04 Ubuntu25.04
== Comment: #3 - Anushree Mathur <Anushree.Mathur2 at ibm.com> - 2026-01-20 02:19:58 ==
Hi Raman,
This is the Network config for Ubuntu25.04
ubuntu at ubuntu:~$ sudo cat /etc/netplan/50-cloud-init.yaml
network:
version: 2
ethernets:
enp0s1:
dhcp4: true
Thanks
== Comment: #4 - Raman Singh <Raman.Singh5 at ibm.com> - 2026-01-20 05:04:37 ==
(In reply to comment #3)
> Hi Raman,
> This is the Network config for Ubuntu25.04
>
> ubuntu at ubuntu:~$ sudo cat /etc/netplan/50-cloud-init.yaml
> network:
> version: 2
> ethernets:
> enp0s1:
> dhcp4: true
>
> Thanks
Netplan yaml file of Ubuntu25.04 does not have "match" tag.
While Ubuntu26.04 have this.
== Comment: #5 - Anushree Mathur <Anushree.Mathur2 at ibm.com> - 2026-01-21 00:08:32 ==
(In reply to comment #4)
> (In reply to comment #3)
> > Hi Raman,
> > This is the Network config for Ubuntu25.04
> >
> > ubuntu at ubuntu:~$ sudo cat /etc/netplan/50-cloud-init.yaml
> > network:
> > version: 2
> > ethernets:
> > enp0s1:
> > dhcp4: true
> >
> > Thanks
>
> Netplan yaml file of Ubuntu25.04 does not have "match" tag.
>
> While Ubuntu26.04 have this.
yes Ubuntu26.04 has that and ubutu25.04 didn't have that.
== Comment: #6 - Raman Singh <Raman.Singh5 at ibm.com> - 2026-01-21 04:26:16 ==
Created mirror request (44922) Canonical Launchpad.
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