Cirros image does not configure MTU according to DHCP

[fwiesel]

It seems the 10-mtu is usually included in other distributions (debian based at least). Copied in plain-text it is just these lines.

# Configure the MTU for the interface
if [ -n "${new_interface_mtu}" ]; then
    ifconfig "${interface}" mtu "${new_interface_mtu}"
fi

[osfrickler]

I've tried to reproduce this, but if I set a custom MTU on some neutron network and then boot a cirros instance in that network, I do see eth0 getting the custom MTU value. Can you add some instructions on how to exactly reproduce your issue? (ideally something that does not involve vmware?) ;)

[fwiesel]

I suspect you could setup a devstack with a non-standard mtu lower than your standard setup like this: https://docs.openstack.org/devstack/rocky/guides/neutron.html#non-standard-mtu-on-the-physical-network

For example:

[[post-config|/$Q_PLUGIN_CONF_FILE]]
global_physnet_mtu = 1450

Our mtu comes from a "standard" neutron network agent with dnsmasq acting as dhcp server.

[osfrickler]

I still cannot reproduce this. Can you share the output of openstack network show for your network and then dhcpcd -U eth0, ip a and cirros-status from your instance?

[fwiesel]

Okay, I have now a KVM hypervisor and there it looks like it should. I'll close it, until I can reproduce it.