OpenStack 10G NIC MTU 9000

Hi Team,

I used separate 10G interfaces for each OpenStack network in my OpenStack setup. MAAS was used to deploy OS on baremetal metal machines. In MAAS there was an option to change the MTU from 1500 to 9000 on each network. If I make a change, will it only apply to bare metal machines or will it also apply MTU 9000 to JUJU VM and LXD containers?

Multi node HA setup: 3 x Controller + 3 CEPH + 10 Compute nodes

MAAS 3.2 + Juju + OpenStack Yoga + Ubuntu Focal

It should apply to all devices running on the physical network. If they run less than what you enter it will be fine. But if any device transmits a larger Packet you will get fragments. A VM should abide by what is designated by the host which means it can broadcast any packet size up to the limit designated.

TL;DR: Plan for what your hardware limitations such as switches may be. If you’re broadcasting publicly choose safer sizes such as 1500. Private network only, feel free to go ham.

I should clarify and perhaps this answers your question better. You will want to define the network before creating the VMs. If you change it afterwards they will likely complain and drop packets.