[PVE-User] mtu setting for virtual ethernet

Konold, Martin martin.konold at konsec.com
Tue Mar 23 13:03:45 CET 2021

Hi Proxmox Users,

I learned from the Proxmox forum that appending mtu=1 to the network 
definition of a virtual machine instructs the virtual ethernet device to 
inherit the mtu from the corresponding bridge.

In my case

net0: virtio=FA:FF:FF:FF:FF:D8,bridge=vmbr15,mtu=1

and the bridge definition

iface vmbr15 inet static
         bridge-ports enp35s0.4015
         bridge-stp off
         bridge-fd 0
         bridge-vlan-aware yes
         bridge-vids 2-4094
         mtu 1400

According to my tests this seams to work indeed. The guest OS shows the 
1400 mtu.

Question 1: Can the mtu=1 (magic value for auto mtu inheritance) be made 
the default?

Question 2: It seams that appending mtu=1 breaks the webUI. I get 
"Unable to parse network options".

Kind Regards
ppa. Martin Konold

Martin Konold - Prokurist, CTO
KONSEC GmbH -⁠ make things real
Amtsgericht Stuttgart, HRB 23690
Geschäftsführer: Andreas Mack
Im Köller 3, 70794 Filderstadt, Germany

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