4.13: unable to increase MTU configuration for GRE devices

Bug #1743746 reported by James Page on 2018-01-17
8
This bug affects 1 person
Affects Status Importance Assigned to Milestone
linux (Ubuntu)
Status tracked in Bionic
Artful
Medium
Joseph Salisbury
Bionic
Medium
Joseph Salisbury

Bug Description

[Impact]
GRE overlay networks can't carry traffic with MTU > 1500

[Test Case]
sudo add-apt-repository cloud-archive:pike
sudo apt update
sudo apt install openvswitch-switch
sudo ovs-vsctl add-br br-tun
sudo ovs-vsctl add-port br-tun gre0 -- set interface gre0 type=gre options:remote_ip=10.100.1.1

gre_sys device will be configured with MTU 1472.

sudo ip link set gre_sys mtu 65000

will fail with EINVAL.

[Regression Potential]

[Bug Report]

Under Linux 4.13 its not possible to configure GRE tunnel devices with a MTU larger than 1500; this impacts on Open vSwitch (which creates tunnel devices for GRE overlay networking) and the ip tools.

The kernel will error with:

  gre_sys: Invalid MTU 65000 requested, hw max 1500

The side effect of this is that if overlay networks are configured with high MTUs, the gre devices fragment the packets and networking is generally slow/broken.

This is resolved as part of the upcoming 4.15 kernel under:

  https://github.com/torvalds/linux/commit/cfddd4c33c254954927942599d299b3865743146

James Page (james-page) on 2018-01-17
description: updated
James Page (james-page) on 2018-01-17
description: updated

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1743746

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

Changed in linux (Ubuntu):
status: New → Incomplete
James Page (james-page) on 2018-01-17
Changed in linux (Ubuntu):
status: Incomplete → Confirmed
Changed in linux (Ubuntu):
importance: Undecided → Medium
status: Confirmed → Triaged
tags: added: kernel-da-key
Changed in linux (Ubuntu):
status: Triaged → In Progress
Changed in linux (Ubuntu Artful):
status: New → In Progress
importance: Undecided → Medium
Changed in linux (Ubuntu):
assignee: nobody → Joseph Salisbury (jsalisbury)
Changed in linux (Ubuntu Artful):
assignee: nobody → Joseph Salisbury (jsalisbury)
Joseph Salisbury (jsalisbury) wrote :

I built a test kernel with commit cfddd4c. The test kernel can be downloaded from:
http://kernel.ubuntu.com/~jsalisbury/lp1743746

Can you test this kernel and see if it resolves this bug?

Note, to test this kernel, you need to install both the linux-image and linux-image-extra .deb packages.

Thanks in advance!

James Page (james-page) wrote :

Hi Joseph

I reconfirmed the bug on the current artful kernel, upgraded to your test kernel and I can confirm that the test kernel resolves the issue:

7: gre_sys@NONE: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65000 qdisc pfifo_fast master ovs-system state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether 3a:14:f5:6d:cd:93 brd ff:ff:ff:ff:ff:ff

I was able to set the MTU of the gre_sys device to 65000.

Joseph Salisbury (jsalisbury) wrote :

Thanks for testing, James. I'll submit an SRU request for this commit to be included in the Ubuntu kernel.

Seth Forshee (sforshee) on 2018-01-19
Changed in linux (Ubuntu Bionic):
status: In Progress → Fix Committed
James Page (james-page) wrote :

Thanks!

James Page (james-page) wrote :

Appreciate the kernel team has been pretty busy the last few months; is there an ETA on when this fix might make it into the 4.13 kernels? I know we've pushed the HWE kernel version forward for xenial - so any OpenStack deployments using HWE with GRE tunnels will hit this problem.

Changed in linux (Ubuntu Artful):
status: In Progress → Fix Committed

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-artful' to 'verification-done-artful'. If the problem still exists, change the tag 'verification-needed-artful' to 'verification-failed-artful'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

tags: added: verification-needed-artful
James Page (james-page) wrote :

LGTM to artful-proposed:

15: gre_sys@NONE: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65000 qdisc pfifo_fast master ovs-system state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether 92:92:4d:84:14:1d brd ff:ff:ff:ff:ff:ff

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 17.10
Release: 17.10
Codename: artful

$ uname -a
Linux juju-9b0cd0-artful-proposed-19 4.13.0-35-generic #39-Ubuntu SMP Mon Feb 12 11:06:39 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

tags: added: verification-done-artful
removed: verification-needed-artful
Timo Aaltonen (tjaalton) wrote :

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-xenial' to 'verification-done-xenial'. If the problem still exists, change the tag 'verification-needed-xenial' to 'verification-failed-xenial'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

tags: added: verification-needed-xenial
tags: removed: verification-needed-xenial
Timo Aaltonen (tjaalton) wrote :

disregard that last comment, it was caused by a buggy script

To post a comment you must log in.
This report contains Public information  Edit
Everyone can see this information.

Other bug subscribers