[Bug 1154378] Re: MTU not set on 'tunnel' interfaces

[Stéphane Graber]

*** This bug is a duplicate of bug 1074048 ***
    https://bugs.launchpad.net/bugs/1074048

** This bug has been marked a duplicate of bug 1074048
   When setting up a GRE tunnel through the 'tunnel' method, the mtu parameter is not respected

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https://bugs.launchpad.net/bugs/1154378

Title:
  MTU not set on 'tunnel' interfaces

Status in “ifupdown” package in Ubuntu:
  New

Bug description:
  Setting MTU via /etc/network/interfaces for GRE tunnels ('tunnel'
  type) doesn't get applied at ifup:

  iface HYDRUS inet tunnel
     mode gre
     address 10.170.1.4
     netmask 255.255.255.254
     endpoint 10.0.0.1
     dstaddr 10.170.1.5
     local 10.255.255.12
     mtu 1472

  37: HYDRUS: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 8976 qdisc noqueue state UNKNOWN
      link/gre 10.255.255.12 peer 10.0.0.1

  It seems to calculate the MTU based on the parent interface's MTU and
  ignore the directive. man 5 interfaces indicates that mtu should be a
  valid option for interfaces of type 'tunnel'. I have worked around
  this with an 'up' directive to manually set the MTU. Upon examining
  the ifupdown.nw source, it appears that MTU is never set for 'tunnel'
  type interfaces. Please rectify or remove it from the documentation.

  $> lsb_release -rd
  Description:    Ubuntu 12.04.1 LTS
  Release:        12.04
  $> apt-cache policy ifupdown
  ifupdown:
    Installed: 0.7~beta2ubuntu8
    Candidate: 0.7~beta2ubuntu8
    Version table:
   *** 0.7~beta2ubuntu8 0
          500 http://mirrors.kernel.org/ubuntu/ precise/main amd64 Packages
          100 /var/lib/dpkg/status

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