[ovs-discuss] OVS MTU regression problem on kernel > 3.11

Reno Gan reno.gan at gmail.com
Sun Oct 5 07:49:04 UTC 2014


Hi,

I installed ubuntu 14.04.1 and tested openswitch GRE tunnel function and 
found a regression problem about MTU. When I use "ping -c 1 -s 1500" to 
ping the remote gre endpoint, the request will hang and the ack will 
never come  back. This problem never happens on kernel version < 
3.12,for example, ubuntu 13.10 or ubuntu 12.04

* What you did that make the problem appear
     - install two nodes with ubuntu 14.04.1, kernel 3.13.0-24
     - openvswitch version is 2.0.2,I did not compiler it, just used 
the default one along with this kernel
     - on one node, configure gre tunnel with the following commands:
         # ovs-vsctl add-br br0
         # ovs-vsctl add-port br0 gre0 -- set Interface gre0 type=gre 
options:remote_ip=10.80.89.125 options:key=1234
         # ip addr add 192.168.1.10/24 dev br0
     - on the other node, configure gre tunnel with the following commands:
         # ovs-vsctl add-br br0
         # ovs-vsctl add-port br0 gre0 -- set Interface gre0 type=gre 
options:remote_ip=10.80.77.154 options:key=1234
         # ip addr add 192.168.1.11/24 dev br0
     - now if I run "ping -c 1 -s 1500 192.168.1.11", the ping ack will 
not come back.

     I also tried to install tow nodes with ubuntu 13.10, kernel 
3.11.0-12,openvswitch version is 1.10.2,use the same commands to set 
up tow nodes, the ping command will return correctly.

     If I use "ping -c 1 -s 1400 192.168.1.11",the ping responds correctly


* What you expected to happen.
     - ping will return correctly with MTU >= 1500.

* Fix or workaround
     - use "ping -c 1 -s 1400 192.168.1.11",ping will respond correctly

I tried openvswitch 2.1.2 on ubuntu 13.10(kernel 3.11),it has no problem.
I also tried openvswitch 2.3.0,compiler and install it on ubuntu 
14.04.1,the same problem appeared. This let me to think it is related 
to new linux kernel.

I found in openvswitch release note:
     Support for Linux kernels up to 3.14. From Kernel 3.12 onwards OVS 
uses tunnel API for GRE and VXLAN.

Could it be possible that new tunnel API caused this regression?

Best Regards,
Reno


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