Home Purchase PDFs FAQ Forums About Contact Quick HOWTO : Ch13 : Linux Wireless Networking From Linux Home Networking Jump to: navigation search Contents Introduction Wireless Linux Compatible NICs Common Wireless Networking Terms 3.1 Wireless Access Points 3.2 Service Set ID 3.3 Encryption 3.3.1 Wired Equivalent Privacy 3.3.2 Wi-Fi Protected Access Networking With Linux Wireless-Tools 4.1 Using iwconfig For wireless-tools Configuration 4.2 Permanent wireless-tools Configuration 4.2.1 Fedora / RedHat 4.2.2 Debian / Ubuntu 4.3 WEP Encryption Configuration 4.3.1 WEP Encryption Configuration 4.3.1.1 WEP Key Generation 4.3.1.1.1 Table 13-1 Byte Count to WEP Key Length Conversion 4.3.1.2 WEP Key Configuration for Fedora / RedHat 4.3.1.3 WEP Key Configuration for Debian / Ubuntu 4.4 WPA Encryption 4.4.1 Installing WPA Supplicant 4.4.2 The wpa_supplicant.conf File 4.4.3 Further WPA Configuration Steps - Fedora / RedHat 4.4.4 Further WPA Configuration Steps - Debian / Ubuntu Configuring Linux with Incompatible Wireless NICs 5.1 Using ndiswrapper 5.2 Installing and Configuring ndiswrapper Troubleshooting Your Wireless LAN 6.1 Check The NIC Status 6.1.1 The iwconfig Command 6.1.2 The iwlist Command 6.1.3 The iwspy Command 6.2 Check For Interrupt Conflicts 6.3 Kernel Errors 6.3.1 Using the /var/log/messages File 6.3.2 Using the dmesg Command 6.4 Can't Ping Default Gateway 6.5 "Unknown Device" Errors 6.6 Hermes Chipset Errors 6.7 Broadcom SoftMac Errors 6.8 ndiswrapper Errors 6.8.1 CONFIG_4KSTACKS errors During Installation 6.8.2 Incorrect Drivers 6.8.3 NICs that are Incompatible with ndiswrapper 6.8.4 Invalid module format Errors 6.9 Wireless Networks In Businesses Conclusion Introduction My very first Linux web server was an ancient desktop computer that I bought from a secondhand store that advertised it as being "very obsolete." It was cheap and it worked, but it was ugly and noisy, so noisy that it quickly became too loud to tolerate. Spending more money than I should have on the antique, I made it wireless so I could take it out of my bedroom where the DSL connection entered my apartment. Looking back, I really did it for the challenge, and also because we all get stupid some of the time. I thought wireless Linux would be easy, but at the time it wasn't. I had so many headaches with it that I thought one of my very first Web pages should be about my little nightmare warning people about how to do it right. This was how www.linuxhomenetworking.com was born. This is the chapter about what started it all. Wireless networks using the 802.11 standard have many advantages, not just the aesthetic one I mentioned. The hardware is commonly available, and wireless networks offer relatively easy and low cost deployment with security that's becoming increasingly better. Before you consider making a Linux server wireless capable, however, make sure you purchase a NIC that is Linux compatible. If this seems confusing, don't worry; I will explain all this later. Wireless Linux Compatible NICs Not all wireless NIC cards work with Linux. For this reason, do your homework. You can find hardware compatibility lists for Wireless Tools quite easily on popular search engines. Wireless NIC manufacturers are notorious for changing the chip sets on their cards depending on the price of the components. They then supply different drivers with each new card to make them work. It is possible to buy cards with the same model number from the same vendor with very different circuitry. Frequently Linux drivers for the new cards are unavailable. Always check the compatibility lists before buying your wireless hardware. The Linksys WMP11 wireless card is a good example of this confusion. The original version of the card used the Intersil Prisim chip set, which worked with Linux, but the newer version 2.7 (Broadcom chip set) and version 4 (InProComm chip set) do not. Even so, the original WMP won't work without upgrading the firmware. In recent years it has become possible to use regular Windows drivers with Linux NICs. This is discussed in more detail in the section titled "Configuring Linux with Incompatible Wireless NICs". The method requires an understanding of Linux Wireless Tools which is covered beforehand, but first, let's cover some wireless networking essentials to provide some background. Note: Don't be fooled. The fact that your Linux system can detect your NIC doesn't mean that it is compatible. Always check the Internet for Linux compatibility listings so that you'll know how to proceed. Common Wireless Networking Terms Learning the ins and outs of wireless Linux networks will be easier if we're all speaking the same language. Before proceeding, take time to become familiar with three key wireless terms: wireless access point, Service Set ID, and shared encryption key. Learn them now, because you'll see them throughout the chapter. Wireless Access Points A wireless access point (WAP) is a device that acts as the central hub of all wireless data communications. In the most common operating mode (Infrastructure mode), all wireless servers communicate with one another via the WAP, which is usually connected to a regular external or integrated router for communication to the Internet. WAPs are, therefore, analogous to switches in regular wired networks. Servers can communicate with one another without a WAP if their NICs are configured in Ad Hoc mode, but this prevents them from communicating with any other communications path. For that, you need a WAP on your network. Service Set ID The 802.11a/b wireless networks typically found in a home environment share the same frequency range with one another so it is possible for your computer to hear the traffic meant for somebody else's nearby network. The Extended Service Set ID (SSID) helps prevent the garbling of messages. Each wireless network needs to be assigned an ESSID that doesn't match that of any neighboring networks within its range of operation. The desired ESSID is then set on both wireless NICs and WAPs, which in turn ignore all traffic using other identifiers. Most wireless software packages enable you to view all the available ESSIDs within range and give you the option of selecting the corresponding wireless LAN (WLAN) to join. Unfortunately, this makes it easy to eavesdrop on a neighboring network, and therefore it is best to not only change your ESSID from the factory defaults, but also to encrypt your wireless data whenever possible. The term ESSID is frequently interchangeably referred to as an SSID (Service Set ID) by many vendors. I'll stick with ESSID unless the term SSID is relevant to an application. Encryption Encryption is a method of encoding or scrambling data so that only people with the secret key to unlock the code can view the original data. As expected, you need to use the same encryption scheme on all devices on your network for communication to be successful.
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