Re: What happens if there are two interfaces?

[Pavel Simerda <psimerda redhat com>]

> From: "Timothy Murphy" <gayleard eircom net>
> To: networkmanager-list gnome org
> Sent: Monday, December 31, 2012 1:44:04 PM
> Subject: Re: What happens if there are two interfaces?
> 
> Nathanael Noblet wrote:
> 
> >> "ip route" just tells me both interfaces are up,
> >> not which one is being used.
> >> Even "ifconfig", which gives the number of packets
> >> passing through each interface,
> >> is not completely conclusive.
> 
> > ip route on my machine gives:
> > default via 192.168.4.1 dev wlan0  proto static
> > 192.168.4.0/24 dev wlan0  proto kernel  scope link  src
> > 192.168.4.103
> > 
> > Which means wlan0 is the default route. Everything goes out that
> > way.
> 
> Yes, thanks for that observation -
> I had overlooked the fact that "ip route" (and "route")
> specify a default interface.
> 
> However, this doesn't completely answer the question.
> You appear to have only one interface active,
> so naturally all packets must go that way.
> I assume that is the situation with most people most of the time.

I know it is tricky to understand this without networking knowledge. But you won't really avoid looking at the actual output of your ip route if you want to learn about your current routing set up. This is what kernel uses to route packets to the network.
 
> My experience with 2 interfaces active, say WiFi and ethernet,
> does not entirely fit in with your theory,
> as ifconfig shows a large number of packets
> going through each interface.

There's a known bug in NetworkManager that breaks connection with wifi and ethernet to the same network (which may be a physically distinct network with the same addressing). Maybe that's what you are experiencing. Maybe not.

> I'll experiment further and see more exactly what happens.
> 
> Incidentally, the reason why the issue arose in my case
> is that one room in my house is at the borderline of WiFi connection.
> Sometimes the connection is made and sometimes it is not.
> So I attached TP-Link homeplugs to my laptop and the server.
> As far as I can make out this works fine under Windows XP,
> but is only partially successful under Fedora.

Shouldn't the homeplug be just ordinary ethernet?

> I also have a very cheap chinese WiFi-Repeater
> which sends out a strong signal as seen by "iwlist scan",
> but is not seen by NM under Fedora, as far as I can see.

What you see in the scan, should be also accessible in NM.

Pavel