Introduction

This article describes some steps for troubleshooting wireless networks using a PCI or PCMCIA adapter

Method

1. Plug in your card and restart the computer.
2. Check whether your computer sees your wireless card. Note the reported model number and manufacturer. The model number may be different from what is written on the manufacturer's label.

   • For PCI cards use

       $ lspci

   • For PCMCIA cards (particularly for notebooks), look at the output of the messages as you insert the PCMCIA card. Something should happen. You should be able to see that the drivers are loaded or a statement that the driver is already loaded

       $ tail -f /var/log/messages

3. Check the wireless extension output. Check whether there is a wireless extension available on any network adapter; there should be at least one if you have inserted a wireless card

     $ iwconfig

   . Some information is only printed if iwconfig is run as root ("sudo iwconfig").

4. Bring up your wireless interface and see what happens. For help on mailing lists, post the output of the command

   $ sudo ifup <ath0>

5. If so far everything works, the card should send DHCP requests to the broadcast IP. If you have not got this far, you're most likely to have a problem with your wireless card driver! And that's a problem by its own.

6. Read again the output of 'iwconfig'. The MAC address of the access point should be stated near the first line. That shows that the card is able to "see" the AP (access point e.g. the router). You may need to use open security mode instead of restricted, depending on the setup of your AP ('iwconfig wlan0 key open PASSWORD'). If you want to write the key in ASCII use 's:' e.g. 'iwconfig wlan0 key restricted s:password'. Set the network name.

7. Check whether the AP can "see" your wireless card.
   • Log into your AP.
   • Find the log files.
   • Does the MAC address of your wireless card should appear there?

     • If not, then most likely your wireless settings are mismatching: Check 'iwconfig' for "Rx invalid nwid" (wrong ESSID), "Rx invalid crypt" (mismatching authentication method/key), "Rx invalid frag" (I haven't got a clue).

       • Usually they show up all together, which should tell you to check your config. Look at '/etc/network/interfaces' (post the output for further inquiries) and compare the settings to the configuration of your AP.

       • If the settings match, try another wireless card.

       • If the settings do not match, change the interfaces file and change the setting with the according iwconfig command (see $ man iwconfig).

8. Check the wireless data rate:

   $ iwconfig

   . With 6.06/Dapper, the default rate seems set at 1 Mbit/sec. Most APs prefer 11M or 54M. Set this manually by

   $ iwconfig <interface> rate 11M

   . Change permanently by adding a line

   wireless-rate 11M

   into the file /etc/network/interfaces.

9. If you are connecting to an ad-hoc (peer-to-peer) network, such as another computer with a peer-to-peer network set up, then set this manually by

    $ iwconfig <interface> mode Ad-Hoc

10. If your card sees the AP and the AP sees you, then probably there is a problem within your network, as this state compares to a plugged-in wire where both interfaces (and the wire) work fine.

    • If you don't get an IP, then check your DHCP server settings

        $ less /etc/dhcp3/dhcpd.conf

    • If you have an IP, try to ping your server to see whether the connection is OK

        $ ping <your server's IP>

    • If you can ping the server, then your wireless connection works; there must be a problem with your service settings.

See Also

• Ubuntu wiki Wireless Main Page

CategoryNetworking CategoryWireless