unable to set mtu on default VLAN

[James Page]

trying to set the MTU on the default vlan for a fabric fails:

{"__all__": ["Cannot modify the default VLAN for a fabric."]}

This really should work; workaround is to set mtu on all interfaces attached to the VLAN.

[Dongwon Cho (dongwoncho)]

It affects me too.

$ maas 1st version read
Success.
Machine-readable output follows:
{
    "subversion": "trusty1",
    "version": "1.9.1+bzr4543-0ubuntu1",
    "capabilities": [
        "networks-management",
        "static-ipaddresses",
        "ipv6-deployment-ubuntu",
        "devices-management",
        "storage-deployment-ubuntu",
        "network-deployment-ubuntu"
    ]
}

$ maas 1st vlan update 0 103 mtu=9000
Success.
Machine-readable output follows:
{
    "name": "",
    "vid": 103,
    "mtu": 9000,
    "fabric": "fabric-0",
    "id": 5003,
    "resource_uri": "/MAAS/api/1.0/vlans/5003/"
}

$ maas 1st vlan update 0 0 mtu=9000
{"__all__": ["Cannot modify the default VLAN for a fabric."]}

[James Page (james-page)]

Interestingly on a Xenial install, if the MTU is mismatched between the vlan interface and the underlying physical network device, you hit:

  https://bugs.launchpad.net/ubuntu/+source/ifupdown/+bug/1565804

Feels like either MAAS or curtin needs to figure out the right MTU settings to pass down into the install so that things all line up?

[Mike Pontillo (mpontillo)]

I feel like if you set the MTU on a VLAN within a fabric, the "default VLAN" MTU should be set to the maximum value of all VLANs within that fabric.

As discussed in the linked bug, it is not possible to have VLANs whose MTU is larger than the base interface, anyway.

Thoughts?