nmcli - fixed false changed status for dummy connections

[Ajpantuso]

SUMMARY

Dummy connections do not default 802-3-ethernet.mtu to auto if no value is explicitly provided. This is in contrast to other connection types which requires an additional check.

Fixes #3612

ISSUE TYPE

• Bugfix Pull Request

COMPONENT NAME

plugins/modules/net_tools/nmcli.py

ADDITIONAL INFORMATION

• Tested against the ethernet connection type to confirm that null mtu does result in auto being set in that case and this is specific to dummy connections

[ansibullbot]

cc @alcamie101
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[haddystuff]

I have checked this fix and have noticed one thing:
If i set mtu some value(for example 1500) in playbook:

- name: nmcli set interface
      nmcli:
        conn_name: dummy_con0
        ifname: dummy0
        ip4: 10.0.0.151/32
        state: present
        type: dummy
        mtu: 1500

Then i deleted mtu value:

- name: nmcli set interface
      nmcli:
        conn_name: dummy_con0
        ifname: dummy0
        ip4: 10.0.0.151/32
        state: present
        type: dummy

nmcli module doesn't detect any changes.
Mtu remains the same(1500) on host.
Correct me if i'm wrong, it seems like it should be set back to auto or be deleted.

[Ajpantuso]

Correct me if i'm wrong, it seems like it should be set back to auto or be deleted.

In this case because there is no true default value I think it's better for no change to be reported (and certainly no action to be taken as the user didn't indicate a desired state). However this is probably an existing issue with the ethernet and team-slave types as those should default to auto when the option is not provided since that's how nmcli behaves.

[haddystuff]

We would have a problem with different interface configuration depending on system initial state. Seem like it's not an expected behavior. Maybe we can do something like this(#3618)?

[Ajpantuso]

We would have a problem with different interface configuration depending on system initial state. Seem like it's not an expected behavior. Maybe we can do something like this(#3618)?

Something like #3618 is possible, but the setting value should be 0 when modifying and auto when checking. However that would be a breaking change.

If you want to ensure consistency instead of omitting the parameter just provide 0 instead.

Using your example:

- name: nmcli set interface
      nmcli:
        conn_name: dummy_con0
        ifname: dummy0
        ip4: 10.0.0.151/32
        state: present
        type: dummy
        mtu: 1500

Will become auto for ethernet, dummy, and team-slave with the below:

- name: nmcli set interface
      nmcli:
        conn_name: dummy_con0
        ifname: dummy0
        ip4: 10.0.0.151/32
        state: present
        type: dummy
        mtu: 0

In effect you are enforcing the default behavior yourself since nmcli is inconsistent.

[haddystuff]

Sorry for reacting too slow, but i came out with this change #3625.
The idea is to change "802-3-ethernet.mtu" to "auto" only if this parameter already exist on interface

[Ajpantuso]

Closing in favor of #3625