cant change the MTU to 9000

[zack_123]

So i have had no luck setting the mtu of my 10 gb nic card I have found this: https://forum.proxmox.com/threads/enable-mtu-9000-jumbo-frames.34523/#post-199464
I have tried pretty much every suggestion for proxmox 5.1 my current /etc/network/interfaces is

auto lo
iface lo inet loopback
iface enp4s0 inet manual
iface enp6s0 inet manual
iface enx8cae4cee5150 inet manual

auto vmbr0
iface vmbr0 inet static
address 192.168.50.50
netmask 255.255.255.0
gateway 192.168.50.1
bridge_ports enp4s0
bridge_stp off
bridge_fd 0
#Wan

auto vmbr1
iface vmbr1 inet static
address 192.168.50.51
netmask 255.255.255.0
bridge_ports enx8cae4cee5150
bridge_stp off

auto vmbr2
iface vmbr2 inet manual
bridge_ports enp6s0
bridge_stp off
bridge_fd 0
ip link set dev enp6s0 mtu 9000
#lan pf sense

auto vmbr3
iface vmbr3 inet static
address 192.168.5.2
netmask 255.255.255.0
bridge_ports vmbr2
bridge_stp off
bridge_fd 0
#USMedia

I have a PfSense kvm witch grabs internet from enp4s0 (1gb nic) witch feeds enp6s0 (10gb nic) card from vmbr2.
I test it from another pc with ping -M do -s 8000 but just says:
ping: local error: Message too long, mtu=1500

I don't know where i'm going wrong I appreciate any help.

 

[Klaus Steinberger]

add "mtu 9000" to the iface definitions of the interfaces:

iface enp4s0 inet manual
mtu 9000

iface enp6s0 inet manual
mtu 9000

iface enx8cae4cee5150 inet manual
mtu 9000

you also have to change mtu in the VM's, the local PC's and _all_ your switches have to support it.
I warn you: if you don't have a strong need (like _very_ high performance filesystem access) don't play around with jumbo frames