Comment 32 for bug 1771749

I have been affected by this one for a time now on a 18.04 LTS install on a laptop with both wired and wireless ethernet. Not a fresh install, but one that had been upgraded from earlier releases.

I have both Wireless and wired ethernet configured. NetworkManager is taking care of network IP address assignment, which is done dynamically on both cases through DHCP from the AP/router.

Every now and then, I get both network interfaces with no IP address assigned whatsoever. It may happen after resuming from suspend (laptop being powered down from hours to days) or while actively using the laptop. In all cases it seems NetworkManager service is still running and "dhclient" processes are up and running for the interfaces. For the latest time this has occured to me:
"""
# service NetworkManager status
● NetworkManager.service - Network Manager
   Loaded: loaded (/lib/systemd/system/NetworkManager.service; enabled; vendor preset: enabled)
   Active: active (running) since Fri 2018-11-16 21:31:31 CET; 4 days ago
     Docs: man:NetworkManager(8)
 Main PID: 845 (NetworkManager)
    Tasks: 5 (limit: 4915)
   CGroup: /system.slice/NetworkManager.service
           ├─ 845 /usr/sbin/NetworkManager --no-daemon
           ├─12154 /sbin/dhclient -d -q -sf /usr/lib/NetworkManager/nm-dhcp-helper -pf /run/dhclient-wlp3s0.pid -lf /var/lib/NetworkManager/dhclient-cef3df46-08a4-4e76-b0d8-3a2c21cd504e-wlp3s0.lease -cf /var/lib/NetworkManager/dhclient-wl
           └─23839 /sbin/dhclient -d -q -sf /usr/lib/NetworkManager/nm-dhcp-helper -pf /run/dhclient-enp0s25.pid -lf /var/lib/NetworkManager/dhclient-7d46e9cc-ee9c-366d-a025-73d355f9d046-enp0s25.lease -cf /var/lib/NetworkManager/dhclient-

# ps -efa | grep Netwo
root 845 1 0 nov16 ? 00:00:20 /usr/sbin/NetworkManager --no-daemon
root 1207 2521 0 14:13 pts/1 00:00:00 grep --color=auto Netwo
root 12154 845 0 nov20 ? 00:00:00 /sbin/dhclient -d -q -sf /usr/lib/NetworkManager/nm-dhcp-helper -pf /run/dhclient-wlp3s0.pid -lf /var/lib/NetworkManager/dhclient-cef3df46-08a4-4e76-b0d8-3a2c21cd504e-wlp3s0.lease -cf /var/lib/NetworkManager/dhclient-wlp3s0.conf wlp3s0
root 23839 845 0 nov20 ? 00:00:00 /sbin/dhclient -d -q -sf /usr/lib/NetworkManager/nm-dhcp-helper -pf /run/dhclient-enp0s25.pid -lf /var/lib/NetworkManager/dhclient-7d46e9cc-ee9c-366d-a025-73d355f9d046-enp0s25.lease -cf /var/lib/NetworkManager/dhclient-enp0s25.conf enp0s25
"""

For me, getting IP addresses assigned again to interfaces is as easy as running "service NetworkManager restart".

Last significant logs in /var/log/syslog prior to losing connectivity (IP address) on both network interfaces (wired "enp0s25" and wireless "wlp3s0") are as below:
"""
#### Wireless interface goes "timed out"
Nov 21 12:13:40 laptop NetworkManager[845]: <info> [1542798820.8236] connectivity: (wlp3s0) timed out
Nov 21 12:13:40 laptop avahi-daemon[841]: Withdrawing address record for 192.168.1.17 on wlp3s0.
Nov 21 12:13:40 laptop avahi-daemon[841]: Leaving mDNS multicast group on interface wlp3s0.IPv4 with address 192.168.1.17.
Nov 21 12:13:40 laptop avahi-daemon[841]: Interface wlp3s0.IPv4 no longer relevant for mDNS.

#### And exactly 20 minutes later so does the wired interface...
Nov 21 12:33:40 laptop NetworkManager[845]: <info> [1542800020.8236] connectivity: (enp0s25) timed out
Nov 21 12:33:40 laptop NetworkManager[845]: <info> [1542800020.8237] manager: NetworkManager state is now CONNECTED_SITE
Nov 21 12:33:40 laptop avahi-daemon[841]: Withdrawing address record for 192.168.1.19 on enp0s25.
Nov 21 12:33:40 laptop systemd[1]: Starting Network Manager Script Dispatcher Service...
Nov 21 12:33:40 laptop avahi-daemon[841]: Leaving mDNS multicast group on interface enp0s25.IPv4 with address 192.168.1.19.
Nov 21 12:33:40 laptop gsd-sharing[1976]: Failed to StopUnit service: GDBus.Error:org.freedesktop.systemd1.NoSuchUnit: Unit gnome-user-share-webdav.service not loaded.
Nov 21 12:33:40 laptop avahi-daemon[841]: Interface enp0s25.IPv4 no longer relevant for mDNS.
Nov 21 12:33:40 laptop gsd-sharing[1976]: Failed to StopUnit service: GDBus.Error:org.freedesktop.systemd1.NoSuchUnit: Unit rygel.service not loaded.
Nov 21 12:33:40 laptop dbus-daemon[812]: [system] Activating via systemd: service name='org.freedesktop.nm_dispatcher' unit='dbus-org.freedesktop.nm-dispatcher.service' requested by ':1.9' (uid=0 pid=845 comm="/usr/sbin/NetworkManager --no-daemon " label="unconfined")
Nov 21 12:33:40 laptop gsd-sharing[1976]: Failed to StopUnit service: GDBus.Error:org.freedesktop.systemd1.NoSuchUnit: Unit gnome-remote-desktop.service not loaded.
Nov 21 12:33:40 laptop dbus-daemon[812]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
Nov 21 12:33:40 laptop systemd[1]: Started Network Manager Script Dispatcher Service.
Nov 21 12:33:40 laptop nm-dispatcher: req:1 'connectivity-change': new request (1 scripts)
Nov 21 12:33:40 laptop nm-dispatcher: req:1 'connectivity-change': start running ordered scripts...
Nov 21 12:33:40 laptop nm-dispatcher: req:2 'connectivity-change': new request (1 scripts)
Nov 21 12:33:40 laptop nm-dispatcher: req:2 'connectivity-change': start running ordered scripts...
Nov 21 12:34:00 laptop whoopsie[1357]: [12:34:00] Cannot reach: https://daisy.ubuntu.com
Nov 21 12:34:00 laptop whoopsie[1357]: [12:34:00] offline
"""

It can't be a coincidence both network devices lose the IP addresses due to some "timed out" event exactly 20 minutes apart. As the event comes from NetworkManager, so must be the bug causing the observed behavior.

Please check if possible to strengthen NetworkManager in the current and upcoming releases. Mine being now:
"""
# cat /etc/os-release
NAME="Ubuntu"
VERSION="18.04.1 LTS (Bionic Beaver)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 18.04.1 LTS"
VERSION_ID="18.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=bionic
UBUNTU_CODENAME=bionic
"""