[Pkg-utopia-maintainers] Bug#1125800: network-manager: Disabling IPv4 manually causes n-m to disconnect after few seconds from IPv6
Witold Baryluk
witold.baryluk at gmail.com
Sun Jan 18 06:47:11 GMT 2026
Package: network-manager
Version: 1.54.3-1+b1
Severity: important
Tags: ipv6
X-Debbugs-Cc: witold.baryluk at gmail.com
I decided to disable manually IPv4 (DHCP) on the interface via gnome
network manager integration.
Network is dual stacked, but I also did setup NAT64 and DNS64, and
things do work, but IPv4 is still prefered (because network manager does
not support DHCP option 108 - aha PREF64, or it is simply not enabled by
default on debian for some reasons - unclear, I do have lxcbr0 with some
IPv4, but I doubt that this is it).
Similarly n-m puts IPv4 nameservers from DHCPv4 at the top of the
/etc/resolv.conf, so the DNS IPv6 servers that are received via IPv6 RA
that are used for DNS64/NAT64 are later in the chain of nameservers
tried, and in practice are never tried. Thus preventing utilization of
nat64 or IPv6-only network. I know there is ipv{4,6}.dns-priority, but
that must be modified on each host, and cannot be influenced right now
by DHCP or RA, or other easy means I think.
Because I cannot influence this via DHCP (other than by mac address or
also disabling IPv4 for all other hosts in that ethernet broadcast
domain), I decided to switch off IPv4 manually on this host / network
interface.
In gnome shell n-m interfae i simply did set IPv4 to Disabled.
IPv6 still at Automatic.
After offlining interface and putting it back online. (Flipping the
toggle in the gnome shell n-m interface), IPv6 works, but gnome-shell
shows that it is still connecting, and after between 5 to 50 seconds I
got an error popup notification ("Connection failed - Activation of
network connection failed"), and interface is taken down, bringing down
IPv6 too.
During that period nmcli shows:
enp65s0f0np0: connecting (getting IP configuration) to Wired connection 1
"Intel E810-C for QSFP"
ethernet (ice), 64:9D:99:11:22:33, hw, sriov, mtu 1500
ip6 default
DNS configuration:
servers: 2001:cafe:bafe:1::64
domains: foo.example.com
interface: enp65s0f0np0
but inspecting "ip a" shows interface up (ra mtu 9000 is ignored but
that is separate maner), SLAAC addresses assigned, routes and defaults
routes assigned to, and even /etc/resolv.conf listing proper
nameserver(s) and dns search list.
Both DNS, IPv6, and DNS64 / NAT64 work perfectly fine for short time
(between 5 and maybe 120 seconds depending on my luck) - tested with
dig, host, curl, firefox, ping, etc.
After disconnecting nmcli shows:
enp65s0f0np0: disconnected
"Intel E810-C for QSFP"
Router is VyOS 1.5, using radv, with nat64 prefix set too (ignored on
Linux, but usable on Android and iPhone), and other generic options that
work fine if I do not disable IPv4 on the debian desktop machine.
This totally looks like a bug in n-m.
root at debian:~# nmcli con edit f662d320-87ec-3fcf-8c29-17814411099a
...
nmcli> print
===============================================================================
Connection profile details (Wired connection 1)
===============================================================================
connection.id: Wired connection 1
connection.uuid: f662d320-87ec-3fcf-8c29-aabbccddee1099a
connection.stable-id: --
connection.type: 802-3-ethernet
connection.interface-name: enp65s0f0np0
connection.autoconnect: yes
connection.autoconnect-priority: -999
connection.autoconnect-retries: -1 (default)
connection.multi-connect: 0 (default)
connection.auth-retries: -1
connection.timestamp: 1768717797
connection.permissions: --
connection.zone: --
connection.controller: --
connection.master: --
connection.slave-type: --
connection.port-type: --
connection.autoconnect-slaves: -1 (default)
connection.autoconnect-ports: -1 (default)
connection.down-on-poweroff: -1 (default)
connection.secondaries: --
connection.gateway-ping-timeout: 0
connection.ip-ping-timeout: 0
connection.ip-ping-addresses: --
connection.ip-ping-addresses-require-all:-1 (default)
connection.metered: unknown
connection.lldp: default
connection.mdns: -1 (default)
connection.llmnr: -1 (default)
connection.dns-over-tls: -1 (default)
connection.mptcp-flags: 0x0 (default)
connection.wait-device-timeout: -1
connection.wait-activation-delay: -1
-------------------------------------------------------------------------------
802-3-ethernet.port: --
802-3-ethernet.speed: 0
802-3-ethernet.duplex: --
802-3-ethernet.auto-negotiate: no
802-3-ethernet.mac-address: --
802-3-ethernet.cloned-mac-address: --
802-3-ethernet.generate-mac-address-mask:--
802-3-ethernet.mac-address-denylist: --
802-3-ethernet.mtu: auto
802-3-ethernet.s390-subchannels: --
802-3-ethernet.s390-nettype: --
802-3-ethernet.s390-options: --
802-3-ethernet.wake-on-lan: default
802-3-ethernet.wake-on-lan-password: --
802-3-ethernet.accept-all-mac-addresses:-1 (default)
-------------------------------------------------------------------------------
ipv4.method: disabled
ipv4.dns: --
ipv4.dns-search: --
ipv4.dns-options: --
ipv4.dns-priority: 0
ipv4.addresses: --
ipv4.gateway: --
ipv4.routes: --
ipv4.route-metric: -1
ipv4.route-table: 0 (unspec)
ipv4.routing-rules: --
ipv4.replace-local-rule: -1 (default)
ipv4.dhcp-send-release: -1 (default)
ipv4.routed-dns: -1 (default)
ipv4.ignore-auto-routes: no
ipv4.ignore-auto-dns: no
ipv4.dhcp-client-id: --
ipv4.dhcp-iaid: --
ipv4.dhcp-dscp: --
ipv4.dhcp-timeout: 0 (default)
ipv4.dhcp-send-hostname-deprecated: yes
ipv4.dhcp-send-hostname: -1 (default)
ipv4.forwarding: -1 (default)
ipv4.dhcp-hostname: --
ipv4.dhcp-fqdn: --
ipv4.dhcp-hostname-flags: 0x0 (none)
ipv4.never-default: no
ipv4.may-fail: yes
ipv4.required-timeout: -1 (default)
ipv4.dad-timeout: -1 (default)
ipv4.dhcp-vendor-class-identifier: --
ipv4.dhcp-ipv6-only-preferred: -1 (default)
ipv4.link-local: 0 (default)
ipv4.dhcp-reject-servers: --
ipv4.auto-route-ext-gw: -1 (default)
ipv4.shared-dhcp-range: --
ipv4.shared-dhcp-lease-time: 0 (default)
-------------------------------------------------------------------------------
ipv6.method: auto
ipv6.dns: --
ipv6.dns-search: --
ipv6.dns-options: --
ipv6.dns-priority: 0
ipv6.addresses: --
ipv6.gateway: --
ipv6.routes: --
ipv6.route-metric: -1
ipv6.route-table: 0 (unspec)
ipv6.routing-rules: --
ipv6.replace-local-rule: -1 (default)
ipv6.dhcp-send-release: -1 (default)
ipv6.routed-dns: -1 (default)
ipv6.ignore-auto-routes: no
ipv6.ignore-auto-dns: no
ipv6.never-default: no
ipv6.may-fail: yes
ipv6.required-timeout: -1 (default)
ipv6.ip6-privacy: -1 (default)
ipv6.temp-valid-lifetime: 0 (default)
ipv6.temp-preferred-lifetime: 0 (default)
ipv6.addr-gen-mode: default
ipv6.ra-timeout: 0 (default)
ipv6.mtu: auto
ipv6.dhcp-pd-hint: --
ipv6.dhcp-duid: --
ipv6.dhcp-iaid: --
ipv6.dhcp-timeout: 0 (default)
ipv6.dhcp-send-hostname-deprecated: yes
ipv6.dhcp-send-hostname: -1 (default)
ipv6.dhcp-hostname: --
ipv6.dhcp-hostname-flags: 0x0 (none)
ipv6.auto-route-ext-gw: -1 (default)
ipv6.token: --
-------------------------------------------------------------------------------
proxy.method: none
proxy.browser-only: no
proxy.pac-url: --
proxy.pac-script: --
-------------------------------------------------------------------------------
-- System Information:
Debian Release: forky/sid
APT prefers testing-debug
APT policy: (500, 'testing-debug'), (500, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386
Kernel: Linux 6.19.0-rc1 (SMP w/32 CPU threads; PREEMPT)
Kernel taint flags: TAINT_CPU_OUT_OF_SPEC, TAINT_UNSIGNED_MODULE
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages network-manager depends on:
ii adduser 3.153
ii dbus [default-dbus-system-bus] 1.16.2-2
ii libaudit1 1:4.1.2-1+b1
ii libbluetooth3 5.84-1
ii libc6 2.42-7
ii libcurl3t64-gnutls 8.18.0~rc2-1
ii libglib2.0-0t64 2.86.3-1
ii libgnutls30t64 3.8.11-3
ii libjansson4 2.14-2+b4
ii libmm-glib0 1.24.2-2
ii libndp0 1.9-1+b1
ii libnewt0.52 0.52.25-1+b1
ii libnm0 1.54.3-1+b1
ii libpsl5t64 0.21.2-1.1+b1
ii libreadline8t64 8.3-3
ii libselinux1 3.9-4+b1
ii libsystemd0 259-1
ii libteamdctl0 1.31-1+b3
ii libudev1 259-1
Versions of packages network-manager recommends:
ii dnsmasq-base [dnsmasq-base] 2.92~rc3-1
ii libpam-systemd 259-1
ii modemmanager 1.24.2-2
ii network-manager-l10n 1.54.3-1
ii polkitd 127-1
ii ppp 2.5.2-1+1.1
ii udev 259-1
ii wireless-regdb 2025.10.07-1
ii wpasupplicant 2:2.10-25
Versions of packages network-manager suggests:
ii iptables 1.8.11-4
ii libteam-utils 1.31-1+b3
Versions of packages network-manager is related to:
pn isc-dhcp-client <none>
-- no debconf information
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