[Pkg-utopia-maintainers] Bug#1021655: network-manager: randomly "forgets" IPv6 default route, resulting in loss of connectivity

[Russell King]

Package: network-manager
Version: 1.30.6-1+deb11u1
Severity: important
Tags: ipv6

Dear Maintainer,

Using Debian Stable on a laptop and on the WiFi router.
WiFi router has network-manager connection sharing enabled to a Linux bridge, to which an ethernet interface and the WiFi AP-mode interface is bound.

Laptop sporadially loses the IPv6 default route, which can be re-gained by disconnecting and reconnecting to the WiFi, or alternatively manually adding it back.

When the default route is removed, existing IPv6 connections (e.g. mosh, ssh etc) hang.

This happens repeatedly, but sporadically.

Nothing appears in the logs on the laptop when the default route is deleted - it seems Network Manager just decides to delete it. The IPv4 default route remains, along with all the other interface configuration. It is only the IPv6 default route that seems to vanish.

-- System Information:
Debian Release: 11.5
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 5.10.0-18-amd64 (SMP w/4 CPU threads)
Kernel taint flags: TAINT_WARN
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages network-manager depends on:
ii  adduser          3.118
ii  dbus             1.12.24-0+deb11u1
ii  libaudit1        1:3.0-2
ii  libbluetooth3    5.55-3.1
ii  libc6            2.31-13+deb11u4
ii  libcurl3-gnutls  7.74.0-1.3+deb11u3
ii  libglib2.0-0     2.66.8-1
ii  libgnutls30      3.7.1-5+deb11u2
ii  libjansson4      2.13.1-1.1
ii  libmm-glib0      1.14.12-0.2
ii  libndp0          1.6-1+b1
ii  libnewt0.52      0.52.21-4+b3
ii  libnm0           1.30.6-1+deb11u1
ii  libpsl5          0.21.0-1.2
ii  libreadline8     8.1-1
ii  libselinux1      3.1-3
ii  libsystemd0      247.3-7+deb11u1
ii  libteamdctl0     1.31-1
ii  libudev1         247.3-7+deb11u1
ii  libuuid1         2.36.1-8+deb11u1
ii  policykit-1      0.105-31+deb11u1
ii  udev             247.3-7+deb11u1
ii  wpasupplicant    2:2.9.0-21

Versions of packages network-manager recommends:
ii  dnsmasq-base [dnsmasq-base]  2.85-1
ii  iptables                     1.8.7-1
ii  libpam-systemd               247.3-7+deb11u1
ii  modemmanager                 1.14.12-0.2
ii  ppp                          2.4.9-1+1
ii  wireless-regdb               2022.04.08-2~deb11u1

Versions of packages network-manager suggests:
ii  isc-dhcp-client  4.4.1-2.3+deb11u1
pn  libteam-utils    <none>

-- no debconf information