Public bug reported: 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. ** Affects: linux Importance: Unknown Status: Unknown ** Affects: linux (Ubuntu) Importance: Medium Status: New ** Tags: kernel-da-key regression-release ** Bug watch added: Linux Kernel Bug Tracker #55861 http://bugzilla.kernel.org/show_bug.cgi?id=55861 ** Also affects: linux via http://bugzilla.kernel.org/show_bug.cgi?id=55861 Importance: Unknown Status: Unknown -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. 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 To manage notifications about this bug go to: https://bugs.launchpad.net/linux/+bug/1160966/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
