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["Christopher M. Penalver" <christopher.m.penalver@xxxxxxxxx>]

** Tags added: needs-kernel-logs raring

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https://bugs.launchpad.net/bugs/1160966

Title:
  PMTU discovery no longer works in Linux 3.6+ with routers that do not
  send next hop MTU information

Status in The Linux Kernel:
  Confirmed
Status in “linux” package in Ubuntu:
  New

Bug description:
  After upgrading to raring, I found that path MTU discovery no longer worked
  correctly for accessing some devices on the other side of an IPsec tunnel.

  Bisection revealed the problems started with 3.6 and are still present in
  3.9-rc4 (latest available at time of reporting).

  Some investigation into code changes leads me to the belief that Linux lost
  support for handling ICMP destination unreachable fragmentation needed packets
  for which the next hop MTU field is zero. This is an expected condition when
  dealing with older routers, as RFC792 originally defined ICMP destination
  unreachable fragmentation needed without a next hop MTU field, and it was later
  added in bytes previously allocated as unused.

  The particular router in my case generating such packets is a machine running
  OpenBSD 4.6.

  A commit that appears to be of particular interest in this bug is
  https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=46517008e1168dc926cf2c47d529efc07eca85c0

  I have also filed this bug in upstream kernel bugzilla as
  https://bugzilla.kernel.org/show_bug.cgi?id=55861 - I'm reporting here
  also to track this as a regression of raring vs. quantal.

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