[TUTORIAL] MTU - Jumbo Frames - Bridge Interface - EXAMPLE Post #3

liszca

Active Member
May 8, 2020
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I want to use Jumbo Frames. From my understanding I have to set the MTU to a value supported by the hardware. But which Interface has to be changed, Bridge Interface or eth0?

When changes are set how can it be tested?
 
You could use the below as an example, and replace or remove the bond configs (in the create stanza as well as the iface) with OVS bridge. This has given me the most flexible way of doing

First and foremost the physical interface must be at the highest mtu that you plan to use.
So using eth0 as an example

iface eth0 inet manual
mtu 9100

then add the bridge to eth0, and set the bridge to the mtu of the interface.

Here is where you will run into problems if you set the higher mtu you must be doing some sort of vlan to support this.
If you don't all interfaces will need to be set at the higher mtu. This means traffic on this bridge will not be able to be used in a normal 1500 MTU network and only traffic within this bridge interface will properly work. (MTU mismatch causing packet fragmentation will occur)

Any VM that is created must then have the MTU set in the creation or update of the VM. This would require setting the advance check in the GUI and placing 1500 in the MTU field.


Gives you some idea of how this can be done and keeps an MTU (1500) that works with one interface and allows normal traffic to flow, i.e. Internet, local workstations.

I used the below to get around the need for this as my switches have full layer 2 support.

Code:
auto enp4s0f0
iface enp4s0f0 inet manual

auto enp4s0f1
iface enp4s0f1 inet manual


auto bond0
allow-netbr0 bond0
iface bond0 inet manual
        ovs_type OVSBond
        ovs_bonds enp4s0f0 enp4s0f1
        ovs_bridge netbr0
        ovs_options bond_mode=balance-tcp lacp=active other_config:lacp-time=fast

auto netbr0
iface netbr0 inet manual
        ovs_type OVSBridge
        ovs_ports bond0 net0
         ovs_mtu 9100 ################################################################       

auto net0
allow-netbr0 net0
iface net0 inet static
        address  0.0.0.2/24
        gateway  0.0.0.1
        dns-nameservers 1.1.1.1
        dns-search
        ovs_type OVSIntPort
        ovs_bridge netbr0
        ovs_options tag=10
        ovs_extra set interface ${IFACE} external-ids:iface-id=$(hostname -s)-${IFACE}-vif
        ovs_mtu 1500 #################################################################
 

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