Comment 0 for bug 1547754

1. If the MTU of eth0 is 1500, network-manager fails to establish a pppoe connection, and the MTU of eth0 (not ppp0) is then automatically lowered to 1492. Now network-manager can successfully establish a pppoe connection. If I manually set the MTU of eth0 back to 1500, network-manager would fail again. See attached log.

2. The Access Concentrator of my ISP offers MTU values of both 1492 and 1442. pppd-4.3.5 in Ubuntu 14.04 adopts 1492 as the MTU of the ppp device, while pppd-4.3.7 in Xenial adopts 1442. Setting the lower MTU on the WAN link (ppp0) can easily cause PMTU-D problems, especially for remote VPN clients.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: network-manager 1.0.4-0ubuntu9
ProcVersionSignature: Ubuntu 4.4.0-6.21-generic 4.4.1
Uname: Linux 4.4.0-6-generic i686
ApportVersion: 2.20-0ubuntu3
Architecture: i386
CurrentDesktop: LXDE
Date: Sat Feb 20 09:56:32 2016
IpRoute:
 default via 172.16.10.1 dev eth0 proto static metric 100
 169.254.0.0/16 dev eth0 scope link metric 1000
 172.16.10.0/24 dev eth0 proto kernel scope link src 172.16.10.32 metric 100
NetworkManager.state:
 [main]
 NetworkingEnabled=true
 WirelessEnabled=false
 WWANEnabled=true
RfKill:
 0: phy0: Wireless LAN
  Soft blocked: yes
  Hard blocked: no
SourcePackage: network-manager
UpgradeStatus: Upgraded to xenial on 2016-02-19 (0 days ago)
WpaSupplicantLog:

nmcli-dev:
 DEVICE TYPE STATE DBUS-PATH CONNECTION CON-UUID CON-PATH
 eth0 ethernet connected /org/freedesktop/NetworkManager/Devices/1 Auto eth0 dff18f4d-6732-4eab-bd06-5209635b9bab /org/freedesktop/NetworkManager/ActiveConnection/11
 irda0 unknown disconnected /org/freedesktop/NetworkManager/Devices/2 -- -- --
 eth1 wifi unavailable /org/freedesktop/NetworkManager/Devices/3 -- -- --
 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'.