SDN testing , changing MTU on specified interface not changing TAP MTU

[Szymons]

Hello,

proxmox 6.3-6 with latest updates
Linux 5.4.106-1-pve #1 SMP PVE 5.4.106-1 (Fri, 19 Mar 2021 11:08:47 +0100) x86_64 GNU/Linux
libpve-network-perl is already the newest version (0.4-6).

I want to change mtu on vlan.
My steps :
I am editing /etc/network/interfaces to insert new MTU.
When I am using "ifreload -a" to do this it is changing MTU setting for vlan but not for TAP's on this vlan.

 

[spirit]

Hi, yes.

for the vm interface, (the tap interface), you need to reduce mtu inside your guest os , or it's possible to define "netX: ....,mtu=1" in vm configuration file (/etc/pve/qemu-server/<vmid>).conf. This is not yet available in the gui.(should be available soon)

 

[Szymons]

Hello,

Thanks for reply.
"This is not yet available in the gui.(should be available soon)"
Now I am using console with ip link set "tap..." mtu XX .
My point was that also console command ifreload not touching this if we change mtu in /etc/network/interfaces .

 

[spirit]

Hello,

Thanks for reply.
"This is not yet available in the gui.(should be available soon)"
Now I am using console with ip link set "tap..." mtu XX .
My point was that also console command ifreload not touching this if we change mtu in /etc/network/interfaces .

yes, this is expected, tap interfaces are not manage by ifupdown or in /etc/network/interfaces.

proxmox create and plug them at vm startup (and set mtu at vm startup).
so you can't juste "update" mtu on /etc/network/interfaces , you also need to stop/start vms (or live migrate them)