Re: NetworkManager: network selection

On Wed, 2015-06-03 at 08:25 +0200, Pieter Cardoen wrote:
Thanks for the reply. It made some things clear. It is for my application not acceptable that the 
NetworkManager just prefers the most recently used network but due to the priority feature, it is possible 
to prefer the WiFi network over a mobile network. However, debian stable doesn't come with NetworkManager 
1.0. I will try to install this version on Debian Jessie.

There are really two kinds of "priority" in NM and they are mostly
independent of each other:

1) connection autoconnect when the device is disconnected, which as
Thomas said can be modified by the 'connection.autoconnect-priority'
property.  This is specific to the device, and all autoconnect decisions
are made independently for that device.

2) which device gets the default route and DNS, which can be modified by
the ip4.route-metric and ip6.route-metric properties.  This allows you
to prefer a specific device for outgoing traffic; so if you want the
WiFi to be preferred when WiFi is connected, then you could set each
WiFi connection's ip4.route-metric property lower (which means "more
preferred") than the WWAN connection's ip4.route-metric property.

Does that make sense?



Subject: Re: NetworkManager: network selection
From: thaller redhat com
To: pieter cardoen hotmail com
CC: networkmanager-list gnome org
Date: Tue, 2 Jun 2015 21:36:41 +0200

On Di, 2015-06-02 at 20:56 +0200, Pieter Cardoen wrote:

I have some questions about how networkmanager selects a network.

How does the NetworkManager deamon decide which network to use if 
multiple network connections are available?


when a device is currently not connected, at various instances
autoconnect hits. For example when you plug-in your cable and carrier
-detect indicates a link. Or when Wi-Fi scanning indicates new visible

So, in that case, NM will search through the non-connected connections
and choose a candidate to autoconnect.

If there are multiple candidates, the one that was used most recently
will be used.

Is it possible to configure preferred networks?

Yes. Such a candidate must have the "connection.autoconnect" property
set to "yes". This is the default. In nm-applet this is called
"Automatically connect to this network when it is available".

Is it possible to configure the NetworkManager to only connect to one 
WiFi network and ignore all other free networks?

Yes, set all connection.autoconnect properties of the other connections
to "no".

Since 1.0, there is also a new property "connection.autoconnect
-priority". You can assign there a number, see
  nmcli connection show CON-NAME
  nmcli connection modify CON-NAME connection.autoconnect-priority 1
  man nm-settings
If there are multiple autoconnect candidates, those with higher numbers
will be preferred.
So, you could set the priority of the connection you prefer to "1",
leaving all others to their default at 0.

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