[ovs-discuss] How does MTU work with tunnels?

Benjamin benjamin.reis at vates.fr
Tue Sep 10 13:03:52 UTC 2019

Hi all,

I working with openvswitch 2.5.3 (tried with 2.11.0 same behavior) on 
XCP-ng (XenServer fork).

I'm trying to undersand how the mtu works with GRE and VxLAN tunnels.
As for now when I create a GRE tunnel with any MTU, I think the MTU is 
not taken in consideration because i can ping -s 15000 on the 
corresponding interface.
However, with VxLAN if I set a MTU greater than 1450 then the MTU is 
1450 and if I set a MTU lower than 1450 I have same behavior as for GRE.

So I'm a but confused.

When I check the mtu value with : ovs-vsctl get int xapi0 mtu_request or 
ovs-vsctl get int xapi0 mtu the returned value is what I expect.

Thanks in advance,


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