Re: Can Anyone Explain the over-all view of Wireless Networking?

On Tue, 02 Feb 2010 14:03:56 -0600
Kent West <westk@xxxxxxx> wrote:

...

Now I get no dhcp offers received. I don't understand how ifup/down and
/etc/modules and udev and /etc/network/interfaces and "wpa-conf
/etc/wpa_supplicant/wpa_supplicant.conf" and iwlist/spy/scan/whatever
and eth0 vs wlan0 vs sit0 and auto eth1 vs allow-hotplug eth1 and wep vs
wep-key vs open vs wpa, etc, all work together.

Basic idea:

1) Hardware support is required for the network card. If you're using
a stock kernel, it's probably there, with some caveats (e.g.,
firmware). In your case, see below.

2) Manually scanning for available networks (iwlist wlan0 scan) - this
is not generally required for routine operation, but is useful for new
locations, or for troubleshooting.

3) Associating the card with the wireless AP - done with 'iwconfig',
or the Debian way, via /etc/network/interfaces. This means that the
card is now 'connected' to the AP, and this sort of parallels the step
of plugging in a cable between a wired card and a switch. If
encryption is being used, you'll need to invoke wpa_supplicant, or some
other application that invokes it. Again, this can be done
via /etc/network/interfaces

4) Configuring IP on the card - you have to do this for wired or
wireless, and the procedure is identical. You can do this manually
(ifconfig wlan0 192.168.0.7) or via dhcp (dhcp wlan0), and once again,
there's the Debian way, via e.n.i.

It should be clear by now that e.n.i. is just a standardized Debian way
of invoking the manual procedures mentioned above. The ifupdown
scripts read the file, and invoke the various underlying commands
(ifconfig, iwconfig, wpa_supplicant) in the appropriate fashion.

If I understood all that, I bet I could figure out how to get my
wireless network working. However, I've been googling/studying off and

Of course you could!

on for the past year, everytime I try to put Debian (or Ubuntu, or
whatever) on a laptop that comes across my path (and failing pretty much
every time on the wireless), but I've never found a site that actually
has gotten me to an understanding of the process. Some sites talk about
gui configuration clients I don't have, or compiling drivers manually
which I don't need to do, or using ndiswrapper (?!), etc.

Maybe the process is just WAY too complex to be explained for mere
mortals who aren't in the mechanics of Linux networking on a daily basis.

So if there's no good explanation out there, perhaps someone can just
help me get it working, without me understanding what's going on. Here's
some relevant information, I believe:

01:08.0 Network controller: Broadcom Corporation BCM4318 [AirForce One
54g] 802.11g Wireless LAN Controller (rev 02)

I have this same Broadcom chipset.

Subsystem: Linksys WMP54GS version 1.1 [Wireless-G PCI Adapter]
802.11g w/SpeedBooster

Well, I certainly don't have this subsystem.

Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR+ FastB2B- DisINTx-
Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort-
<TAbort- <MAbort- >SERR- <PERR- INTx-
Latency: 64
Interrupt: pin A routed to IRQ 17
Region 0: Memory at feade000 (32-bit, non-prefetchable) [size=8K]
Kernel driver in use: b43-pci-bridge

westk@evoljasen:~$ sudo iwlist wlan0 scan
wlan0 Scan completed :

Okay, so you have a bunch of cells with the same ESSID, but different
addresses. IIUC, that sounds like an enterprise setup, but it
shouldn't make a difference, or be a problem for us. Encryption is not
in use.

westk@evoljasen:~$ cat /etc/network/interfaces

...

auto wlan0
iface wlan0 inet dhcp
# wireless_essid humanslivehere
wireless-essid ACUWireless open
wireless-keymode open
#wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

I'd leave the 'open' out of the wireless-essid line.

(the wired interface works with the above setup. the wireless works at
the other location (humanslivehere) when that line and the wpa-conf
lines are uncommented and the other two uncommented lines are not in the
file)

westk@evoljasen:~$ cat /etc/wpa_supplicant/wpa_supplicant.conf
ctrl_interface=/var/run/wpa_supplicant
ctrl_interface_group=users
#
# humanslivehere
network={
ssid="humanslivehere"
psk="it's a secret"
}

wpa_supplicant (generally?) isn't relevant where encryption isn't in
use. It may be helpful for roaming, but shouldn't be necessary for a
basic connection.

westk@evoljasen:~$ sudo iwspy
lo Interface doesn't support wireless statistic collection

eth1 Interface doesn't support wireless statistic collection

wmaster0 Interface doesn't support wireless statistic collection

wlan0 Interface doesn't support wireless statistic collection

You don't need to bother with this.

westk@evoljasen:~$ sudo /etc/init.d/networking restart

You can also simply do 'ifup wlan0'.

...

Listening on LPF/eth1/00:0d:56:2c:5e:d6

This is the networking subsystem activating eth1 (the wired interface).

Sending on LPF/eth1/00:0d:56:2c:5e:d6
Sending on Socket/fallback
DHCPRELEASE on eth1 to 150.252.128.107 port 67
There is already a pid file /var/run/dhclient.wlan0.pid with pid 18812
killed old client process, removed PID file
Internet Systems Consortium DHCP Client V3.1.3
Copyright 2004-2009 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/wlan0/00:18:f8:29:b5:96
Sending on LPF/wlan0/00:18:f8:29:b5:96
Sending on Socket/fallback
DHCPRELEASE on wlan0 to 192.168.1.1 port 67
send_packet: Network is unreachable
send_packet: please consult README file regarding broadcast address.
Internet Systems Consortium DHCP Client V3.1.3
Copyright 2004-2009 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/eth1/00:0d:56:2c:5e:d6
Sending on LPF/eth1/00:0d:56:2c:5e:d6
Sending on Socket/fallback
DHCPDISCOVER on eth1 to 255.255.255.255 port 67 interval 7
DHCPDISCOVER on eth1 to 255.255.255.255 port 67 interval 9
DHCPOFFER from 150.252.8.1
DHCPREQUEST on eth1 to 255.255.255.255 port 67
DHCPACK from 150.252.46.1
bound to 150.252.12.59 -- renewal in 79090 seconds.

Okay, so configuration of the wired interface is working fine.

Internet Systems Consortium DHCP Client V3.1.3
Copyright 2004-2009 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/wlan0/00:18:f8:29:b5:96

This is the networking subsystem attempting to configure the wireless
interface.

Sending on LPF/wlan0/00:18:f8:29:b5:96
Sending on Socket/fallback
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 4
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 11
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 11
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 10
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 13
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 7
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 5
No DHCPOFFERS received.
No working leases in persistent database - sleeping.
done.

It is failing. Now, IME, most such failures are due to the card not
being properly associated with the AP. You can determine this by
either looking at syslog, or by calling 'iwconfig wlan0'. If it's
properly associated, the first two lines should be something like this:

wlan0 IEEE 802.11bg ESSID:"nnnnnnn"
Mode:Managed Frequency:2.437 GHz Access Point: 12:34:56:78:99:aa

If it's not, you'll see something like this:

wlan0 IEEE 802.11bg ESSID:off/any
Mode:Managed Access Point: Not-Associated

Information in syslog will be helpful in determining the cause of failure.

Celejar
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