Re: Multiple WLAN Routers with same SSID

[Dan Williams <dcbw redhat com>]

On Thu, 2012-09-20 at 23:37 +0200, Petric Frank wrote:
> Hello Dan,
> 
> Am Donnerstag, 20. September 2012, 19:19:52 schrieb Dan Williams:
> > On Thu, 2012-09-20 at 18:13 +0200, Petric Frank wrote:
> > > at my location i sometimes notice that different WLAN-routers broadcasts
> > > the same SSID, but different frequencies and MAC-addresses. They also
> > > require different (WPA1/2-) keys to access. But i have only the access
> > > key of one of this access points.
> > 
> > So this is somewhat bad network planning, because it means you cannot
> > roam between access points.  That's somewhat worked around by the
> > locking to WPA1 vs. WPA2.  NM actually *does* have the functionality to
> > lock a connection to WPA1 or WPA2, but it's not exposed in the UI
> > because it's incredibly stupid planning on the part of network
> > engineers, and in 6 years this is only the second case we've heard of
> > that would require that.
> 
> These networks are not owned/managed by me. So i don't have the possibility to 
> get then changed.
> You seem have the impression that i am in the task of network planning. This 
> is not true - i am a simple end user on this subject.

I know you can't change it.  And we have to work around it.  Just
cathartically pointing some fingers.

> > However, we'll probably end up adding an option to expose the
> > WPA1/WPA2/Automatic option in the UI by setting a gsettings key to
> > expose it.  These dialogs already have enough toggles :(
> > 
> > > The autoconnect feature of nm-applet (and hence network manager) seems to
> > > select the host to connect only by the SSID - which often fails.
> > 
> > Correct, because with WiFi the SSID *is* the network; wifi networks with
> > the same SSID are expected to be backed by the same core network, and
> > you're expected to be able to roam between these APs.
> 
> In fact (here in Germany) german telecom delivered WLAN-routers which all have 
> preset the same (E)SSID. Shall i go to every household (even if i can locate 
> them) in my environment to tell them to change their SSID ?

Well, same situation here in the US with Linksys consumer routers, where
by default they all use "linksys" and nobody bothers to change it.  But
the difference here is that these devices are used in a *home*, not a
business or campus.  That means that we can assume that every "linksys"
or "netgear" is *not* the same network, and that you're *not* expected
to roam between these access points.  So what users need to do here is
lock the connection to a BSSID (ie, a single AP) instead, and then NM
will only try to connect to the specific AP you've told it to.

However, at a campus or business where all access points have the same
name, you *are* expected to be able to roam between access points, and
so a network like you describe where half the access points have one
passphrase and the other have have a different passphrase is unhelpful.
But obviously you can't fix that.

> Therefor i asked to use an other key additionaly
> 
> > > Could i suggest to implement and use (/store) the MAC address of the WLAN
> > > access point as additional selection key (maybe optionally) ?
> > 
> > This is already implemented as the "BSSID" option in the connection
> > editor; setting this to the BSSID of the access point you'd like to
> > connect to will limit that connection to only that AP. 
> 
> I saw the field in nm-applet's config system. What should be put into this field 
> - the MAC address of the access point in question ?

Yes, you put the MAC address of the AP into this field (also called a
BSSID).

> If it is an SSID it does not help me, because of duplicate SSIDs (as written 
> above).
> At one time i was at a location where i saw 4 access points in range 
> announcing the same SSID. These access points were *no* roaming ones, they 
> seemed completely different dedicated ones.

Yes, like "linksys" or "netgear" or "alice" you need to lock the
connection to the specific AP you want to use, otherwise NM,
wpa_supplicant, and the kernel have no idea which one to use, and will
happily attempt to roam between access points.  This isn't an
NM-specific behavior, often the kernel drivers or supplicant will roam
between access points too, because that's how WiFi is expected to work.

> The MAC address of the access point's wlan interface (if not changed by the 
> owner) is the unique key of it - as far as i know.
> The can be see by issuing for example
>   iwlist <wlan if> list
> 
> in the line
>   Cell xx: Address <MAC>
> 
> > This however
> > does break roaming quite spectacularly, because it disables roaming
> > completely.  If you don't need roaming at all, try this.
> 
> I do not need roaming for them.

Good.  Then locking the connection to a specific MAC address/BSSID will
work well for you.

Dan