[Bug 1499827] [NEW] [ipv6] Network manager incorrectly lowers MTU when IPv6 is enabled

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Sebastien Bacher (seb128):

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'.

** Affects: network-manager
     Importance: Medium
         Status: Fix Released

** Affects: network-manager (Ubuntu)
     Importance: High
         Status: Confirmed


** Tags: amd64 apport-bug wily
-- 
[ipv6] Network manager incorrectly lowers MTU when IPv6 is enabled
https://bugs.launchpad.net/bugs/1499827
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