Re: Device Priority - Modem and Wi-Fi

On Tue, 2014-09-23 at 11:03 -0500, Dan Williams wrote:
On Mon, 2014-09-22 at 17:33 +0200, Thomas Haller wrote:
On Fri, 2014-09-19 at 21:21 -0500, Kevin Baker wrote:
Hello all,

I was wondering if there was some justification for the priority
listing in src/nm-device.c: nm_device_get_priority(). Specifically,
that a MODEM connection is higher in the priority than a WIFI

Note that this is not for connection priority support within the same
device type (like bug 580018 [1]), but across different devices,
mainly for the default route.

The reason for asking is that our device will automatically activate a
Wi-Fi connection when it is detected in range, and fall back to a 3G
Modem if it goes out of range / is unavailable. This works great,
however since WiFi is given lower priority by NM, the default route
stays on the 3G connection all the time.

Is this just a historical thing? Having WiFi priority over Modem would
also match other platforms such as Android. I can submit the patch we
are using to swap these (super simple) if desired.


The priority of MODEM vs. WIFI was changed by commit:

before, the priority was based on nm_device_get_device_type(), with

I don't know the reasons for that change.

nm_device_get_priority() was/is used both for the autoconnect-priority
and route-metric.
Back then, we also accepted a change of behavior and I think a
behavioral change now would be acceptable as well.

And I tend to agree that WIFI should have higher priority then MODEM.

I believe the decision was made to prioritize WWAN over WiFi since WWAN
is typically more expensive (and WiFi is usually "free") therefore you
are more likely to intentionally connect WWAN and disconnect it when
done, but WiFi can mostly autoconnect without $$ surprises.  At least
that's the current theory.

Yeah, this is inflexible.  Thomas is also working on removing this
restriction as we speak.


Oh, I was wrong. This has nothing to do with autoconnect and
autoconnect-priority (bgo#580018). It's about which device gets the
default route and which route metric will be assigned by default.

bgo#735512 will add the possibility for the user to overwrite the
default priorities. Regardless of that, the question still stands,
whether we want to prefer WWAN over WiFi by default.


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