[vox-tech] Wireless Networking

[Chanoch (Ken) Bloom]

On Wed, Jul 28, 2010 at 12:42:36PM -0400, Peter Salzman wrote:
> I'm having a horrendously awful time getting wireless networking working on
> my Kubuntu box.   I've never played around with wireless networking on Linux
> before and wanted to consolidate my knowledge and see if I understand it
> correctly.   My two wireless cards are:
> 
> Edimax EW-7318usg
>      148F:2573 Ralink Technology, Corp. RT2501USB wireless adapter
> 
> Alfa AWUS050NH
>      148F:2770 Ralink Technology, Corp.
> 
> If this were wired networking, the steps I would take would be:
> 
> 1. Plug in the card into the computer and connect it to the router.
> 2. Load the correct driver.
> 3. Bring the interface up and assign an IP addr, either manually with
> ifconfig or automatically with dhclient.
> 3a. If manual was used in step 3, resolv.conf must contain the DNS servers
> and a gateway must be specified with "route".
> 
> I assume wireless networking must work more or less the same way.   The two
> things that are causing me grief are:
> 
> 1. I don't know if the drivers are correct.

dmesg should clue you in to that.
You can also run ifconfig -a or iwconfig to see whether the interface
appears in the list. If that works, then your driver works. (Well, if
it appears in the list but doesn't work, then you're into bug hunting,
really.)

> 2. Security details (WEP, WPA, etc)

Use wpasupplicant.

wpasupplicant maintains a configuration file with a list of networks
and their encryption types and passwords. When you run wpasupplicant,
it looks to see what's available that it knows about, picks one and
connects (to the wireless router -- then it's your job to set up the
IP address yourself.) If it doesn't know about any of the available
networks, it doesn't connect to any of them, even if they're
unencrypted.

For some security confiurations (pretty much only WEP), you can use
iwconfig.  iwconfig is the low level tool for connecting
to the network.  It doesn't remember anything about any networks (kinda
like how ifconfig works) 

Either way, you can check whether it worked by running iwconfig -- it
it says "Access Point: Not-Associated", you failed. If it gives a MAC
address, then you succeded.

Your new set of steps:

1. Plug in the card into the computer and connect it to the router.
  (check by looking at dmesg to see the USB subsystem recognizes that
  it was plugged in.)
2. Load the correct driver. (May happen automatically by udev)
  (check by running ifconfig -a to see what name the interface was
  given)
3. Bring the interface up and connect to a wireless network
  option 1: use wpa_supplicant for all of this.
  option 2: use ifconfig/iwconfig for the various steps
  (check by running iwconfig to see whether it's associated with a
  particular MAC address. Maybe you could do some kind of arp lookup
  at this point also.)
4. Assign an IP address
  option 1: dhclient
  option 2: ifconfig/route/vi resolv.conf
  (check by pinging something)

In general, you probably want to use something like network-manager or
wicd to handle connecting to wireless networks. Even if you'd
ordinarily prefer to write your own networking configuration script,
or hard code information in  /etc/network/interfaces, and let Debian
do it for you you're most likely going to be using a lot more
different networks (with a lot more varied configurations) with your
wireless card than you typically do with your wired ethernet.

If you've reached the driver step and successfully loaded the driver,
you can watch the state of your wireless card in real time using wavemon
It will show you signal strength, which AP you're associated with, and
your IP address as they change (which can be useful to have in another
window while you're fighting through the details of configuring the
network.)

> Part of the problem is that there seems to be a LOT of information out
> there, and some of it is conflicting.  For example, which drivers to use for
> these wireless cards.  When I load a driver, is there some way of finding
> out if the driver is functional for the card?   It would remove a lot of the
> later guesswork if I had confidence that the driver loaded is correct and
> working.
> 
> The 2nd question concerns security.  If you want to use WPA2/AES, is
> wpa_supplicant mandatory to use?
> 
> Since the obvious way to know if networking is functional is to ping a
> remote host, if it doesn't work, it's not clear at what stage the process is
> failing at.   Is there a way to detect that everything is AOK up to
> wpa_suplicant without having to switch the router's security completely off?
> 
> Thanks!
> Pete

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-- 
Chanoch (Ken) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/