Hoi Artyom,

Not an authoritative answer, although perhaps Damjan can confirm:
Is the semantic difference between max frame size (==device will reject
frames larger than that on Rx, and never Tx frames larger than that) and
mtu (L3 IP/IP6/MPLS packets will not be larger than that) with an
implication that MTU can bever be larger than max_frame_size.

Regardless, Artyom, here's how I manipulate the MTU of VXLAN tunnels - the
trick is to use the 'mtu packet' rather than 'mtu' option (see the CLI call
in bold):

create vxlan tunnel instance 10 src $A dst $B vni 320501 decap-next l2
set interface state vxlan_tunnel10 up

*set interface mtu packet 1522 vxlan_tunnel10*set interface l2 xconnect
TenGigabitEthernet5/0/0.50 vxlan_tunnel10
set interface l2 xconnect vxlan_tunnel10 TenGigabitEthernet5/0/0.50

pim@ddln1:~$ vppctl show ver
vpp v22.06-rc0~93-g360aee3e0 built by pim on dellr610 at 2022-02-13T11:56:07

pim@ddln1:~$ vppctl show int vxlan_tunnel10
              Name               Idx    State  MTU (L3/IP4/IP6/MPLS)
Counter          Count
vxlan_tunnel10                    17     up          *1522/0/0/0*     rx
packets                209408
                                                                    rx
bytes                81834552
                                                                    tx
packets               1616124
                                                                    tx
bytes              2471872228

Does that help for you? I actually noticed that it doesn't prevent
vxlan_tunnel10 from emitting larger frames, so I'm not quite sure what
benefit it brings.

On Thu, Feb 17, 2022 at 11:38 AM Artyom Glazychev <
artyom.glazyc...@xored.com> wrote:

> Hello,
>
> There is a problem with setting MTU for VxLAN. I see, that there was a
> change related to MTU and Max_frame_size -
> https://gerrit.fd.io/r/c/vpp/+/34928
>
> I don't know, what VxLAN configuration is right (I've asked about it here
> https://lists.fd.io/g/vpp-dev/topic/vxlan_l3_mode/89205942?p=,,,20,0,0,0::recentpostdate/sticky,,,20,2,0,89205942,previd=1645090589967474984,nextid=1643993575016104745&previd=1645090589967474984&nextid=1643993575016104745
> )
>
> But neither this:
> DBGvpp# create vxlan tunnel src 10.0.3.1 dst 10.0.3.3 vni 55 l3
> vxlan_tunnel0
> DBGvpp# set interface mtu 1400 vxlan_tunnel0
> set interface mtu: Unsupported (underlying driver doesn't support changing
> Max Frame Size)
>
> Nor this:
> DBGvpp# create vxlan tunnel src 10.0.3.1 dst 10.0.3.3 vni 55
> vxlan_tunnel0
> DBGvpp# set interface mtu 1400 vxlan_tunnel0
> set interface mtu: not supported
> is not working.
>
> So, my final question is how to configure the VxLAN L2-tunnel and set MTU?
> Thank you.
>
>
> 
>
>

-- 
Pim van Pelt <p...@ipng.nl>
PBVP1-RIPE - http://www.ipng.nl/
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