[ovs-dev] Odd gre_sys MTU setting (2.6.x vs 2.8.x)

[James Page]

On Tue, 16 Jan 2018 at 16:26 James Page <james.page at ubuntu.com> wrote:

> On Tue, 16 Jan 2018 at 16:23 James Page <james.page at ubuntu.com> wrote:
>
>>
>> On Tue, 16 Jan 2018 at 15:47 Eric Garver <e at erig.me> wrote:
>> [...]
>>
>>> > Re-tested with the mainline kernel; gre_sys device is still configured
>>> with
>>> > a 1472 MTU, however I was then able to increase it using ip link set
>>> > gre_sys mtu XXXX, confirming that the kernel applied hardware limit
>>> was not
>>> > longer being enforced - however looks like the IFLA_MTU settings
>>> provided
>>> > from OVS are still being ignored by the kernel.
>>>
>>> What was the value of XXXX? Did you try 66535 (what OVS uses)? Any dmesg
>>> for the OVS case?
>>>
>>
>> Good question:
>>
>> # ip link set gre_sys mtu 65535
>> RTNETLINK answers: Invalid argument
>> # ip link set gre_sys mtu 9000
>> # ip link
>> [...]
>> 18: gre_sys at NONE: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc
>> pfifo_fast master ovs-system state UNKNOWN mode DEFAULT group default qlen
>> 1000
>>     link/ether ea:38:bd:61:29:4d brd ff:ff:ff:ff:ff:ff
>>
>> so the value set by OVS was not accepted using ip as well.
>>
>
> 65490 was the largest MTU value I am able to set via the ip command
>

And to confirm no error messages in dmesg.