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[Bug 1177507] Re: per route mtu settings are broken in linux kernel 3.2

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** Tags added: refused-troubleshooting

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https://bugs.launchpad.net/bugs/1177507

Title:
  per route mtu settings are broken in linux kernel 3.2

Status in “linux” package in Ubuntu:
  Confirmed

Bug description:
  Hello,

  Looks like setting per route mtu (as described in [1]) is broken in linux kernel 3.2 (default kernel from ubuntu 12.04).
  I made script to illustrate this:

  root@germany7:~# cat route-mtu
  #!/bin/bash

  uname -a
  ip tuntap add dev test mode tun
  ifconfig test 10.1.1.1/16 mtu 1500
  echo =============================================================
  echo No per route mtu entry
  ping -c1 -Mdo -s2000 10.1.1.2
  echo =============================================================
  echo Per route MTU is set to 800
  ip route add  10.1.1.2 dev test proto static src 10.1.1.1 mtu lock 800
  ip route flush cache
  ping -c1 -Mdo -s2000 10.1.1.2
  ip route del 10.1.1.2 dev test proto static src 10.1.1.1 mtu lock 800
  echo =============================================================
  echo Per route MTU is set to 600
  ip route add  10.1.1.2 dev test proto static src 10.1.1.1 mtu lock 600
  ip route flush cache
  ping -c1 -Mdo -s2000 10.1.1.2
  ip route del 10.1.1.2 dev test proto static src 10.1.1.1 mtu lock 600
  echo =============================================================
  echo No per route mtu entry
  ip route flush cache
  ping -c1 -Mdo -s2000 10.1.1.2
  ip tuntap del dev test mode tun

  With kernel 3.2 I get following output:
  Linux germany7 3.2.0-41-generic-pae #66-Ubuntu SMP Thu Apr 25 03:50:20 UTC 2013 i686 i686 i386 GNU/Linux
  =============================================================
  No per route mtu entry
  PING 10.1.1.2 (10.1.1.2) 2000(2028) bytes of data.
  From 10.1.1.1 icmp_seq=1 Frag needed and DF set (mtu = 1500)

  --- 10.1.1.2 ping statistics ---
  0 packets transmitted, 0 received, +1 errors

  =============================================================
  Per route MTU is set to 800
  PING 10.1.1.2 (10.1.1.2) 2000(2028) bytes of data.
  From 10.1.1.1 icmp_seq=1 Frag needed and DF set (mtu = 800)

  --- 10.1.1.2 ping statistics ---
  0 packets transmitted, 0 received, +1 errors

  =============================================================
  Per route MTU is set to 600
  PING 10.1.1.2 (10.1.1.2) 2000(2028) bytes of data.
  From 10.1.1.1 icmp_seq=1 Frag needed and DF set (mtu = 800)

  --- 10.1.1.2 ping statistics ---
  0 packets transmitted, 0 received, +1 errors

  =============================================================
  No per route mtu entry
  PING 10.1.1.2 (10.1.1.2) 2000(2028) bytes of data.
  From 10.1.1.1 icmp_seq=1 Frag needed and DF set (mtu = 800)

  --- 10.1.1.2 ping statistics ---
  0 packets transmitted, 0 received, +1 errors

  After once set to 800, MTU is always 800, even if you add different
  route and clean routing cache.

  It looks like that problem is fixed in ubuntu kernel 3.5. With it, everything works like expected:
  root@germany7:~# ./route-mtu
  Linux germany7 3.5.0-28-generic #48~precise1-Ubuntu SMP Wed Apr 24 21:43:05 UTC 2013 i686 i686 i386 GNU/Linux
  =============================================================
  No per route mtu entry
  PING 10.1.1.2 (10.1.1.2) 2000(2028) bytes of data.
  From 10.1.1.1 icmp_seq=1 Frag needed and DF set (mtu = 1500)

  --- 10.1.1.2 ping statistics ---
  0 packets transmitted, 0 received, +1 errors

  =============================================================
  Per route MTU is set to 800
  PING 10.1.1.2 (10.1.1.2) 2000(2028) bytes of data.
  From 10.1.1.1 icmp_seq=1 Frag needed and DF set (mtu = 800)

  --- 10.1.1.2 ping statistics ---
  0 packets transmitted, 0 received, +1 errors

  =============================================================
  Per route MTU is set to 600
  PING 10.1.1.2 (10.1.1.2) 2000(2028) bytes of data.
  From 10.1.1.1 icmp_seq=1 Frag needed and DF set (mtu = 600)

  --- 10.1.1.2 ping statistics ---
  0 packets transmitted, 0 received, +1 errors

  =============================================================
  No per route mtu entry
  PING 10.1.1.2 (10.1.1.2) 2000(2028) bytes of data.
  From 10.1.1.1 icmp_seq=1 Frag needed and DF set (mtu = 1500)

  --- 10.1.1.2 ping statistics ---
  0 packets transmitted, 0 received, +1 errors

  I also tested with kernels 2.6.35 (in lucid) and 3.8 (in precise),
  results are same to 3.5.

  Is there any chance to get fixes from 3.5/3.8 backported to the
  default precise kernel 3.2?

  1. http://lartc.org/howto/lartc.cookbook.mtu-discovery.html
  --- 
  AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.24.
  ApportVersion: 2.0.1-0ubuntu17.2
  Architecture: i386
  ArecordDevices:
   **** List of CAPTURE Hardware Devices ****
   card 0: Intel [HDA Intel], device 0: ALC268 Analog [ALC268 Analog]
     Subdevices: 1/1
     Subdevice #0: subdevice #0
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  yura       2759 F.... pulseaudio
  Card0.Amixer.info:
   Card hw:0 'Intel'/'HDA Intel at 0xf4800000 irq 45'
     Mixer name	: 'Intel Cantiga HDMI'
     Components	: 'HDA:10ec0268,1025013c,00100101 HDA:14f12c06,10250093,00100000 HDA:80862802,80860101,00100000'
     Controls      : 23
     Simple ctrls  : 10
  CheckboxSubmission: 02f685f3381c5341bcbab31fdf0318b9
  CheckboxSystem: 8278c9e6a57f68452a782d8924c0633a
  DistroRelease: Ubuntu 12.04
  HibernationDevice: RESUME=UUID=2d28cf13-ba1f-4394-9958-51ed5ccb4dd3
  MachineType: Acer Extensa 5630
  MarkForUpload: True
  Package: linux (not installed)
  PccardctlIdent:
   Socket 0:
     no product info available
  PccardctlStatus:
   Socket 0:
     no card
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: root=UUID=8f05626d-62de-43a5-87f9-1e51af186021 ro quiet splash resume=UUID=70081498-3f3e-4d20-8ccb-c31aebd900d6
  ProcVersionSignature: Ubuntu 3.2.0-41.66-generic 3.2.42
  RelatedPackageVersions:
   linux-restricted-modules-3.2.0-41-generic N/A
   linux-backports-modules-3.2.0-41-generic  N/A
   linux-firmware                            1.79.4
  Tags:  precise
  Uname: Linux 3.2.0-41-generic i686
  UpgradeStatus: Upgraded to precise on 2013-05-09 (0 days ago)
  UserGroups: adm admin disk fuse pulse-access src sudo users wireshark
  WpaSupplicantLog:
   
  dmi.bios.date: 08/05/2008
  dmi.bios.vendor: Phoenix Technologies LTD
  dmi.bios.version: V1.19
  dmi.board.name: Homa
  dmi.board.vendor: Acer
  dmi.board.version: Rev
  dmi.chassis.type: 10
  dmi.chassis.vendor: Acer
  dmi.chassis.version: N/A
  dmi.modalias: dmi:bvnPhoenixTechnologiesLTD:bvrV1.19:bd08/05/2008:svnAcer:pnExtensa5630:pvr0100:rvnAcer:rnHoma:rvrRev:cvnAcer:ct10:cvrN/A:
  dmi.product.name: Extensa 5630
  dmi.product.version: 0100
  dmi.sys.vendor: Acer

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