Re: Learning ifpludg in CLI, WAS Re: laptop wireless setup, wpa_supplicant.conf, etc

[Brian <ad44@cityscape.co.uk>]

On Mon 31 Oct 2011 at 12:53:21 -0700, keitho@strucktower.com wrote:

> If I boot the laptop with the Ethernet cable plugged in (eth0), that
> connection works fine. If I then unplug the Ethernet cable I can not
> connect to the outside world via the wireless (eth1). Yet I can ping
> machines inside my own LAN:

Immediately after boot /sbin/route shows:
-----------------------------------------

  Destination  Gateway      Genmask         Flags Metric Ref Use Iface
  default      192.168.7.1  0.0.0.0         UG    0      0     0 eth0
  localnet     *            255.255.255.0   U     0      0     0 eth0
  localnet     *            255.255.255.0   U     0      0     0 wlan0

eth0 is brought up by ifplugd because the cable is connected. wlan0 is
brought up because of 'allow-hotplug wlan0' in /e/n/i. Quite why there
is only one default route, I'm unsure. Pinging locally and to the
outside world is possible.

Unplug the cable:
-----------------

  Destination  Gateway      Genmask         Flags Metric Ref Use Iface
  localnet     *            255.255.255.0   U     0      0     0 wlan0

eth0 is taken down by ifplugd. wpa_supplicant runs

    wpa_cli -i wlan0 reconnect

from action_wpa.sh but nothing happens because wlan0 is not disconnected
in the first place. There is only local connectivity.

> However, if I then plug the Ethernet cable back in, wait a few moments,
> then unplug it a second time, now the eth1 can ping outside my LAN.
> 
> After this, ifplugd works as intended- Ethernet plugged in eth0 works,
> unplugged eth1 works. But it needs that second round of unplugging to get
> eth1 to ping the outside world. Any ideas?

Cable plugged back in.
----------------------

  Destination  Gateway      Genmask         Flags Metric Ref Use Iface
  default      192.168.7.1  0.0.0.0         UG    0      0     0 eth0
  localnet     *            255.255.255.0   U     0      0     0 eth0

wpa_supplicant does

    wpa_cli -i wlan0 disconnect

which has effect because wlan0 is connected. ifplugd brings up eth0.

The second cable unplugging:
----------------------------

I bet you can work out what happens now!

Removing the 'allow-hotplug wlan0' line in /e/n/i avoids a few cable
manipulations but you will have to remember there will be no wireless
connection if you boot with a cable unattached. Swings and roundabouts.

Just to complicate matters; after booting it is also possible to get:

  Destination  Gateway      Genmask         Flags Metric Ref Use Iface
  default      192.168.7.1  0.0.0.0         UG    0      0     0 wlan0
  localnet     *            255.255.255.0   U     0      0     0 wlan0
  localnet     *            255.255.255.0   U     0      0     0 eth0

I suppose there is a element of chance involved in which interface is
configured first.