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[nemith <1499827@xxxxxxxxxxxxxxxxxx>]

** Summary changed:

- [ipv6] Network manager spews logs of Lowering IPv6 MTU (1480) to match device MTU (1280)
+ [ipv6] Network manager incorrectly lowers MTU when IPv6 is enabled

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https://bugs.launchpad.net/bugs/1499827

Title:
  [ipv6] Network manager incorrectly lowers MTU when IPv6 is enabled

Status in NetworkManager:
  Fix Released
Status in network-manager package in Ubuntu:
  Confirmed

Bug description:
  Network manager is sending out a lot of warnings about changing the MTU:
  Sep 25 14:13:03 desktop NetworkManager[703]: <warn>  (wlan0): Lowering IPv6 MTU (1480) to match device MTU (1280)
  Sep 25 14:13:21 desktop NetworkManager[703]: <warn>  (wlan0): Lowering IPv6 MTU (1480) to match device MTU (0)
  Sep 25 14:13:21 desktop NetworkManager[703]: <warn>  (wlan0): IPv6 MTU (0) smaller than 1280, adjusting
  Sep 25 14:13:21 desktop NetworkManager[703]: <warn>  (wlan0): Raising device MTU (0) to match IPv6 MTU (1280)
  Sep 25 14:13:29 desktop NetworkManager[703]: <warn>  (wlan0): Lowering IPv6 MTU (1480) to match device MTU (1280)

  Lowering IPv6 MTU (1480) to match device MTU (1280) repeats about 16
  times between the other messages (about 2 mins round).

  
  This doesn't appear to be Ubuntu specific - https://bbs.archlinux.org/viewtopic.php?pid=1552751

  ProblemType: Bug
  DistroRelease: Ubuntu 15.10
  Package: network-manager 1.0.4-0ubuntu3
  ProcVersionSignature: Ubuntu 4.2.0-11.13-generic 4.2.1
  Uname: Linux 4.2.0-11-generic x86_64
  NonfreeKernelModules: nvidia
  ApportVersion: 2.19-0ubuntu1
  Architecture: amd64
  CurrentDesktop: Unity
  Date: Fri Sep 25 14:09:20 2015
  IfupdownConfig:
   # interfaces(5) file used by ifup(8) and ifdown(8)
   auto lo
   iface lo inet loopback
  InstallationDate: Installed on 2015-01-08 (259 days ago)
  InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Alpha amd64 (20150108)
  NetworkManager.state:
   [main]
   NetworkingEnabled=true
   WirelessEnabled=true
   WWANEnabled=true
   WimaxEnabled=true
  RfKill:
   0: phy0: Wireless LAN
   	Soft blocked: no
   	Hard blocked: no
  SourcePackage: network-manager
  UpgradeStatus: Upgraded to wily on 2015-08-12 (43 days ago)
  nmcli-nm: Error: command ['nmcli', '-f', 'all', 'nm'] failed with exit code 2: Error: Object 'nm' is unknown, try 'nmcli help'.

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