WiFi problem, loss of DHCP/DNS when changing from one SSID to another but OK from turn on

[Chris Green]

On Sat, Feb 10, 2018 at 07:51:00PM +0000, Chris Green wrote:
> I am having a problem with WiFi connections from my Lenovo laptop
> running xubuntu 17.10.
> 
> I have a number of different WiFi sources round our rather rambling
> house so the laptop has to move from one to another as I move around.
> 
> When moving to one SSID in particular it always fails to get proper
> settings via DHCP, in fact it acts rather as if DHCP fails altogether.
> Network Manager tells me I'm connected but the WiFi has no IP address
> and thus, obviously, no functional connection.
> 
> If I turn the laptop off and power it up then it connects OK to the
> same SSID.  If I just reset the laptop it *doesn't* connect
> successfully.  Connecting to other SSIDs around the house doesn't seem
> to suffer from the same problem, it's just one SSID where this
> happens. (I'm pretty sure this is the case but I've not spent a very
> long time checking).
> 
> I've found that if I do "nmcli off" followed by "nmcli on" (as root of
> course) then I get a good connection again.  Disconnecting and
> reconnecting from the Network Manager applet in the panel doesn't
> clear the problem though.
> 
> Does anyone have any suggestions as to what might be wrong?
> 
Just to add some further information running 'nmcli monitor' shows the
following for an unsuccessful connection:-

    Networkmanager is now in the 'disconnected' state
    wlp4s0: disconnected
    wlp4s0: connecting (prepare)
    wlp4s0: using connection '2860n'
    Networkmanager is now in the 'connecting' state
    wlp4s0: connecting (need authentication)
    wlp4s0: connecting (prepare)
    wlp4s0: connecting (configuring)
    2860n: connection profile changed
    wlp4s0: connecting (getting IP configuration)
    wlp4s0: connecting (checking IP connectivity)
    wlp4s0: connecting (starting secondary connections)
    wlp4s0: connected
    Networkmanager is now in the 'connected (local only)' state

whereas for a successful connection I see:-

    Networkmanager is now in the 'disconnected' state
    Networkmanager is now in the 'connecting' state
    wlp4s0: connecting (prepare)
    wlp4s0: using connection '2820n'
    wlp4s0: connecting (need authentication)
    2820n: connection profile changed
    wlp4s0: connecting (prepare)
    wlp4s0: connecting (configuring)
    wlp4s0: connecting (getting IP configuration)
    wlp4s0: connecting (starting secondary connections)
    wlp4s0: connected
    '2820n' is now the primary connection
    Networkmanager is now in the 'connected' state
    Connectivity is now 'full'

-- 
Chris Green