Config for any Debian-based distro (Mint, Ubuntu, Proxmox, Debian itself, etc.)

Add line mtu 9000

/etc/network/interfaces

auto lo
iface lo inet loopback

iface enp2s0f0 inet manual
    mtu 9000  # for fiber 10g nic

iface enp3s0 inet manual

iface enp4s0 inet manual

iface enp2s0f1 inet manual
    mtu 9000  # for fiber 10g nic

auto vmbr0
iface vmbr0 inet static
    address 192.168.2.2/24
    gateway 192.168.2.1
    bridge-ports enp2s0f0 enp2s0f1
    bridge-stp off
    bridge-fd 0
    mtu 9000  # for bridge

source /etc/network/interfaces.d/*

reload config

ifreload -a

Verify MTU configured previous

ip link show enp2s0f0
ip link show enp2s0f1
ip link show vmbr0

output should include “mtu 9000”