Public bug reported:
Summary
With IPv6 set to "Automatic" on a wired connection (netplan-managed), name
resolution does not work after a clean boot. Raw IPv4/IPv6 connectivity works.
Toggling IPv6 to disabled and back to automatic fixes it until the next boot.
A Fedora machine on the same network does not show the problem.
Environment
- Ubuntu release: <24.04 / 26.04, output of lsb_release -rd>
- network-manager: 1.54.3-2ubuntu3 <check with: apt policy network-manager>
- systemd/systemd-resolved: <apt policy systemd>
- Interface: enp12s0, wired Ethernet, NM connection "netplan-enp12s0"
- Reproduced on both Ubuntu 24.04 and 26.04 <confirm>
Steps to reproduce
1. Set IPv6 method to "Automatic" for the wired connection.
2. Reboot.
3. Run: ping -c3 google.com
Expected result
Name resolution works (DNS servers from DHCPv4/DHCPv6/RA are applied).
Actual result
"Temporary failure in name resolution".
- ping 1.1.1.1 and ping -6 2001:4860:4860::8888 succeed.
- resolvectl status shows "Current Scopes: none" and no DNS servers on enp12s0.
- nmcli device show enp12s0 shows:
IP4.DNS[1]: 192.168.128.1
IP6.DNS[1]: fe80::ce00:f1ff:fe6f:1fb2
IP6.DNS[2]: ::
- NetworkManager journal at boot:
dhcp6 (enp12s0): state changed new lease
dns-sd-resolved[...]: send-updates SetLinkDNS@2 failed:
GDBus.Error:org.freedesktop.DBus.Error.InvalidArgs: Invalid DNS server
address
(repeated three times, also after the dhcp4 lease)
Analysis
NetworkManager appears to include the unspecified address "::" in the DNS
list it sends to systemd-resolved via SetLinkDNS. resolved rejects the whole
call, so none of the servers (including the valid IPv4 one) are applied.
NetworkManager should probably filter out invalid entries such as "::" before
calling SetLinkDNS. I have not yet confirmed whether the router's DHCPv6 reply
actually contains "::" or whether it originates elsewhere.
Workaround
nmcli connection modify netplan-enp12s0 ipv6.ignore-auto-dns yes
(or dhcp6-overrides: use-dns: false in netplan)
Attachments
ubuntu-bug attachments, plus the NM journal and nmcli output above.
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: network-manager 1.54.3-2ubuntu3.1
ProcVersionSignature: Ubuntu 7.0.0-38.38-generic 7.0.14
Uname: Linux 7.0.0-38-generic x86_64
ApportVersion: 2.34.1-0ubuntu0.1
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Sat Oct 17 18:10:20 2026
InstallationDate: Installed on 2026-10-17 (0 days ago)
InstallationMedia: Ubuntu 26.04.1 LTS "Resolute Raccoon" - Release amd64
(20260826)
IpRoute:
default via 192.168.128.1 dev enp12s0 proto dhcp src 192.168.129.10 metric 100
192.168.128.0/23 dev enp12s0 proto kernel scope link src 192.168.129.10 metric
100
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=xterm-256color
XDG_RUNTIME_DIR=<set>
RfKill:
0: hci0: Bluetooth
Soft blocked: no
Hard blocked: no
SourcePackage: network-manager
UpgradeStatus: No upgrade log present (probably fresh install)
nmcli-dev:
DEVICE TYPE STATE IP4-CONNECTIVITY
IP6-CONNECTIVITY DBUS-PATH CONNECTION
CON-UUID CON-PATH
enp12s0 ethernet connected full none
/org/freedesktop/NetworkManager/Devices/2 netplan-enp12s0
4f08c9e6-92c9-395f-b774-0ffcc4dde86f
/org/freedesktop/NetworkManager/ActiveConnection/4
lo loopback connected (externally) unknown unknown
/org/freedesktop/NetworkManager/Devices/1 lo
885841dd-9132-4522-a6fc-a0529805e81a
/org/freedesktop/NetworkManager/ActiveConnection/1
enxf01e34143084 ethernet unavailable none none
/org/freedesktop/NetworkManager/Devices/3 -- --
--
nmcli-nm:
RUNNING VERSION STATE STARTUP CONNECTIVITY NETWORKING WIFI-HW WIFI
WWAN-HW WWAN METERED
running 1.54.3 connected started full enabled missing
enabled missing enabled no (guessed)
** Affects: network-manager (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute wayland-session
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https://bugs.launchpad.net/bugs/2171300
Title:
NetworkManager passes "::" as DNS server to systemd-resolved
(SetLinkDNS "Invalid DNS server address"), leaving link with no DNS
after boot
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