I installed Ubuntu 15.10 in VMware Workstation 12 Player to give it a try and I noticed that the network disconnects and reconnects every several minutes. I can't see this in other virtual machines or in the host machine (which runs Ubuntu 14.04 LTS). Here is a part of the syslog:
Sep 19 14:04:49 ubuntu NetworkManager[725]: <info> (eno16777736): link disconnected (deferring action for 4 seconds)
Sep 19 14:04:49 ubuntu kernel: [ 6157.643978] e1000: eno16777736 NIC Link is Down
Sep 19 14:04:53 ubuntu NetworkManager[725]: <info> (eno16777736): link disconnected (calling deferred action)
Sep 19 14:04:53 ubuntu NetworkManager[725]: <info> (eno16777736): device state change: activated -> unavailable (reason 'carrier-changed') [100 20 40]
Sep 19 14:04:53 ubuntu NetworkManager[725]: <info> (eno16777736): canceled DHCP transaction, DHCP client pid 23002
Sep 19 14:04:53 ubuntu NetworkManager[725]: <info> (eno16777736): DHCPv4 state changed bound -> done
Sep 19 14:04:53 ubuntu avahi-daemon[721]: Withdrawing address record for 172.16.110.138 on eno16777736.
Sep 19 14:04:53 ubuntu avahi-daemon[721]: Leaving mDNS multicast group on interface eno16777736.IPv4 with address 172.16.110.138.
Sep 19 14:04:53 ubuntu avahi-daemon[721]: Interface eno16777736.IPv4 no longer relevant for mDNS.
Sep 19 14:04:53 ubuntu avahi-daemon[721]: Withdrawing address record for fe80::20c:29ff:fed8:4c0c on eno16777736.
Sep 19 14:04:53 ubuntu avahi-daemon[721]: Leaving mDNS multicast group on interface eno16777736.IPv6 with address fe80::20c:29ff:fed8:4c0c.
Sep 19 14:04:53 ubuntu avahi-daemon[721]: Interface eno16777736.IPv6 no longer relevant for mDNS.
Sep 19 14:04:53 ubuntu NetworkManager[725]: <info> Writing DNS information to /sbin/resolvconf
Sep 19 14:04:53 ubuntu whoopsie[693]: [14:04:53] Cannot reach: https://daisy.ubuntu.com
Sep 19 14:04:53 ubuntu whoopsie[693]: [14:04:53] Cannot reach: https://daisy.ubuntu.com
Sep 19 14:04:53 ubuntu dnsmasq[829]: setting upstream servers from DBus
Sep 19 14:04:53 ubuntu NetworkManager[725]: <info> NetworkManager state is now CONNECTED_LOCAL
Sep 19 14:04:53 ubuntu NetworkManager[725]: <info> NetworkManager state is now DISCONNECTED
Sep 19 14:04:53 ubuntu dbus[611]: [system] Activating via systemd: service name='org.freedesktop.nm_dispatcher' unit='dbus-org.freedesktop.nm-dispatcher.service'
Sep 19 14:04:53 ubuntu systemd[1]: Starting Network Manager Script Dispatcher Service...
Sep 19 14:04:53 ubuntu dbus[611]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
Sep 19 14:04:53 ubuntu systemd[1]: Started Network Manager Script Dispatcher Service.
Sep 19 14:04:53 ubuntu nm-dispatcher: Dispatching action 'down' for eno16777736
Sep 19 14:04:54 ubuntu gnome-session[2339]: (deja-dup-monitor:2783): GLib-CRITICAL **: Source ID 211 was not found when attempting to remove it
Sep 19 14:04:54 ubuntu org.freedesktop.Notifications[2212]: ** Message: resizing pixbuf to 44
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> (eno16777736): link connected
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> (eno16777736): device state change: unavailable -> disconnected (reason 'carrier-changed') [20 30 40]
Sep 19 14:04:55 ubuntu kernel: [ 6163.654550] e1000: eno16777736 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> Device 'eno16777736' has no connection; scheduling activate_check in 0 seconds.
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> Auto-activating connection 'Wired connection 1'.
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> (eno16777736): Activation: starting connection 'Wired connection 1' (63e6e203-d873-4bdb-b106-bc9cf709d023)
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> (eno16777736): device state change: disconnected -> prepare (reason 'none') [30 40 0]
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> NetworkManager state is now CONNECTING
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> (eno16777736): device state change: prepare -> config (reason 'none') [40 50 0]
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> (eno16777736): device state change: config -> ip-config (reason 'none') [50 70 0]
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> Activation (eno16777736) Beginning DHCPv4 transaction (timeout in 45 seconds)
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> dhclient started with pid 23200
Sep 19 14:04:55 ubuntu dhclient: DHCPREQUEST of 172.16.110.138 on eno16777736 to 255.255.255.255 port 67 (xid=0x162927e3)
Sep 19 14:04:55 ubuntu dhclient: DHCPACK of 172.16.110.138 from 172.16.110.254
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> address 172.16.110.138
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> plen 24 (255.255.255.0)
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> gateway 172.16.110.2
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> server identifier 172.16.110.254
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> lease time 1800
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> nameserver '172.16.110.2'
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> domain name 'localdomain'
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> wins '172.16.110.2'
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> (eno16777736): DHCPv4 state changed unknown -> bound
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> (eno16777736): device state change: ip-config -> ip-check (reason 'none') [70 80 0]
Sep 19 14:04:55 ubuntu avahi-daemon[721]: Joining mDNS multicast group on interface eno16777736.IPv4 with address 172.16.110.138.
Sep 19 14:04:55 ubuntu avahi-daemon[721]: New relevant interface eno16777736.IPv4 for mDNS.
Sep 19 14:04:55 ubuntu avahi-daemon[721]: Registering new address record for 172.16.110.138 on eno16777736.IPv4.
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> (eno16777736): device state change: ip-check -> secondaries (reason 'none') [80 90 0]
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> (eno16777736): device state change: secondaries -> activated (reason 'none') [90 100 0]
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> NetworkManager state is now CONNECTED_LOCAL
Sep 19 14:04:55 ubuntu whoopsie[693]: [14:04:55] Cannot reach: https://daisy.ubuntu.com
Sep 19 14:04:55 ubuntu whoopsie[693]: [14:04:55] Cannot reach: https://daisy.ubuntu.com
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> NetworkManager state is now CONNECTED_GLOBAL
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> Policy set 'Wired connection 1' (eno16777736) as default for IPv4 routing and DNS.
Sep 19 14:04:55 ubuntu dnsmasq[829]: setting upstream servers from DBus
Sep 19 14:04:55 ubuntu dnsmasq[829]: using nameserver 172.16.110.2#53
Sep 19 14:04:55 ubuntu dhclient: bound to 172.16.110.138 -- renewal in 842 seconds.
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> Writing DNS information to /sbin/resolvconf
Sep 19 14:04:55 ubuntu NetworkManager[725]: <info> (eno16777736): Activation: successful, device activated.
Sep 19 14:04:55 ubuntu nm-dispatcher: Dispatching action 'up' for eno16777736
Sep 19 14:04:55 ubuntu whoopsie[693]: [14:04:55] The default IPv4 route is: /org/freedesktop/NetworkManager/ActiveConnection/5
Sep 19 14:04:55 ubuntu whoopsie[693]: [14:04:55] Not a paid data plan: /org/freedesktop/NetworkManager/ActiveConnection/5
Sep 19 14:04:55 ubuntu whoopsie[693]: [14:04:55] Found usable connection: /org/freedesktop/NetworkManager/ActiveConnection/5
Sep 19 14:04:55 ubuntu org.freedesktop.Notifications[2212]: ** Message: resizing pixbuf to 44
Sep 19 14:04:55 ubuntu gnome-session[2339]: (deja-dup-monitor:2783): GLib-CRITICAL **: Source ID 211 was not found when attempting to remove it
Sep 19 14:04:55 ubuntu whoopsie[693]: [14:04:55] online
Sep 19 14:04:56 ubuntu avahi-daemon[721]: Joining mDNS multicast group on interface eno16777736.IPv6 with address fe80::20c:29ff:fed8:4c0c.
Sep 19 14:04:56 ubuntu avahi-daemon[721]: New relevant interface eno16777736.IPv6 for mDNS.
Sep 19 14:04:56 ubuntu avahi-daemon[721]: Registering new address record for fe80::20c:29ff:fed8:4c0c on eno16777736.*.
ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: network-manager 1.0.4-0ubuntu3
ProcVersionSignature: Ubuntu 4.2.0-10.12-generic 4.2.0
Uname: Linux 4.2.0-10-generic x86_64
ApportVersion: 2.18.1-0ubuntu1
Architecture: amd64
CurrentDesktop: Unity
Date: Sat Sep 19 14:08:34 2015
IfupdownConfig:
# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback
InstallationDate: Installed on 2015-09-19 (0 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Alpha amd64 (20150919)
IpRoute:
default via 172.16.110.2 dev eno16777736 proto static metric 100
169.254.0.0/16 dev eno16777736 scope link metric 1000
172.16.110.0/24 dev eno16777736 proto kernel scope link src 172.16.110.138 metric 100
IwConfig:
eno16777736 no wireless extensions.
lo no wireless extensions.
NetworkManager.state:
[main]
NetworkingEnabled=true
WirelessEnabled=true
WWANEnabled=true
WimaxEnabled=true
RfKill:
SourcePackage: network-manager
UpgradeStatus: No upgrade log present (probably fresh install)
nmcli-con:
NAME UUID TYPE TIMESTAMP TIMESTAMP-REAL AUTOCONNECT AUTOCONNECT-PRIORITY READONLY DBUS-PATH ACTIVE DEVICE STATE ACTIVE-PATH
Wired connection 1 63e6e203-d873-4bdb-b106-bc9cf709d023 802-3-ethernet 1442696839 Sat 19 Sep 2015 02:07:19 PM PDT yes 0 no /org/freedesktop/NetworkManager/Settings/0 yes eno16777736 activated /org/freedesktop/NetworkManager/ActiveConnection/5
nmcli-dev:
DEVICE TYPE STATE DBUS-PATH CONNECTION CON-UUID CON-PATH
eno16777736 ethernet connected /org/freedesktop/NetworkManager/Devices/1 Wired connection 1 63e6e203-d873-4bdb-b106-bc9cf709d023 /org/freedesktop/NetworkManager/ActiveConnection/5
lo loopback unmanaged /org/freedesktop/NetworkManager/Devices/0 -- -- --
nmcli-nm: Error: command ['nmcli', '-f', 'all', 'nm'] failed with exit code 2: Error: Object 'nm' is unknown, try 'nmcli help'.
Status changed to 'Confirmed' because the bug affects multiple users.