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Chapter 14, as well as those referred to in Chapters 15 and 16 for methods of securing your network, its computers, and their services. Manually Configuring Wireless Cards Because the Network Configuration window includes only the basic settings you need to configure a wireless LAN in Linux, fine-tuning your wireless LAN cards requires some manual configuration. Also, if you are running Red Hat Linux as a router or server with no GUI, you may need to configure your wireless LAN manually. You can manually configure Red Hat Linux with two files using the /etc/pcmcia/config.opts file and a configuration file in the /etc/sysconfig/network-scripts directory. Caution If you have used this wireless interface on other Linux systems, you may be used to configuring the card from settings in the wireless .opts and config.opts file (in the /etc/pcmcia directory). In Red Hat Linux, settings made in the Network Configuration window will override those placed in the config.opts and wireless.opts files. Thus, Because of that fact, whenever possible you should configure your wireless card using the Network Configuration window or by adding settings to your wireless interface configuration file in the /etc/sysconfig/network-scripts directory. You can add the following kinds of information to the config.opts and wireless.opts files to manually configure a wireless card: Module options Once you determine which module is used for your wireless card, you can pass options to that module when it starts up, using entries in the config.opts file. Examples of options that you can pass to several different wireless cards are contained in that file. Wireless extensions After the module is loaded, you can set or change wireless extensions on the running module using the iwconfig command. Any options that you want to set permanently can be added to the script representing the wireless interface in the /etc/sysconfig/network-scripts directory or to the wireless.opts file. Because not all wireless cards support all features, you should refer to driver-specific documentation associated with your card to see what parameters and wireless extensions you can set with the iwconfig command. Tip Man pages contain the most specific configuration information for each wireless card driver. Type the man command, followed by any of the following driver names that are appropriate for your card: airo_cs, airo, wavelan_cs, wavelan, wvlan_cs, or netwave_cs. For the Orinoco wireless LAN cards, I typed man wvlan_cs. Setting module options Before you can add module options, you need to determine which module is used to drive your wireless card (see the sidebar “Determining your wireless card’s module”). Determining your wireless card’s module There are several ways to determine the module used to drive your wireless card. Table 25-1 shows drivers for several popular wireless cards. Unfortunately, you can’t always tell what’s inside the card from the name on the box. You can simply insert the card in your PCMCIA slot. If the card beeps twice, look in the /var/log/messages
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Your wireless LAN should be operating at this point. If you are not able to communicate with other wireless nodes or if transmission is slow, you may have more work to do. For example, if you see messages that say “Destination Host Unreachable”, instead of the output shown above, refer to the section on “Troubleshooting a wireless LAN” for help. If you want to fine-tune your wireless interface, refer to the “Manually configuring wireless cards” section that follows. Testing out distances Although you may be thrilled to have a wireless LAN working between two computers, you will probably want these computers to be located some distance from each other to make the LAN useful. Getting your wireless LAN to work at the desired distances can be quite a challenge. See the section titled “Selecting antennas” earlier in this chapter for suggestions on selecting and using antennas to configure the type of wireless LAN you are interested in. Wireless Security The Wireless Ethernet Compatibility Alliance (WECA) recently presented recommendations in response to security concerns about wireless networks. Unlike wired networks where you can often physically protect your wires within a building, wireless networks often extend outside physical boundaries that can be protected. Wireless Equivalent Privacy (WEP) adds encryption to the 802.11 wireless standard. WECA refers to WEP as its way of providing “walls” that make wireless Ethernet as secure as wired Ethernet. However, you need to implement WEP, as well as other security methods that would apply to any computer network, for your wireless network to be most secure. Here are WECA’s suggestions: Change the default WEP encryption key and change the key you use on a regular basis (possibly weekly or even daily for more security). This prevents casual drive-by hackers from being able to read your encrypted transmissions. Use password protection on your drives and folders. Change the default ESSID (Network ID). Use session keys if available in your product (session keys are not supported in current Linux wireless drivers). Use MAC address filtering (which is supported in a limited way in Linux). Use a VPN system, which can add another layer of encryption beyond that which is available on your wireless network. For larger organizations requiring greater security, WECA suggests such features as firewalls or user verification schemes (such as Kerberos). As I mentioned earlier in this chapter, features for protecting from intrusions and restricting services are already built into Red Hat Linux. Refer to the security tools described in
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net.ipv4.ip_forward = 1 Repeat this procedure for all wireless Red Hat Linux computers on your LAN. At this point, your wireless network should be ready to go. Restart your network, as described in the following steps, to make sure that it is working. Restart wireless interfaces To cause the information you just entered to take effect for your wireless cards, simply restart the PCMCIA interface on your Linux computer. You can then test that you can communicate between the two wireless computers using standard TCP/IP tools (such as the ping command). To restart the wireless interfaces, type the following as root user from a Terminal window on each of the wireless computers: # /etc/init.d/pcmcia restart Shutting down PCMCIA services: cardmgr modules. Starting PCMCIA services: modules cardmgr When the service stops, the card will beep once. When it restarts, it should beep twice. If it doesn t, either the card isn’t seated properly or the card’s module or adapter card isn’t configured properly. To check that the two wireless nodes can communicate, try the ping command. For example, if the IP address of the first computer were 172.31.0.10, type the following from the second computer: $ ping 172.31.0.10 PING 172.31.0.10 (172.31.0.10) from 172.31.0.11 : 56(84) bytes of data 64 bytes from 172.31.0.10: icmp_seq=0 ttl=255 time=6.195 msec 64 bytes from 172.31.0.10: icmp_seq=1 ttl=255 time=2.872 msec 64 bytes from 172.31.0.10: icmp_seq=2 ttl=255 time=2.037 msec 64 bytes from 172.31.0.10: icmp_seq=3 ttl=255 time=2.065 msec — 172.31.0.10 ping statistics — 4 packets transmitted, 4 packets received, 0% packet loss round trip min/avg/max/mdev = 1.037/3.292/6.195/1.709 ms Type Ctrl-d to end the ping command. If packets are transmitted and received without error, you have completed your wireless LAN connection! You can now use this connection as you would any wired Ethernet LAN. Depending on your intended use of this LAN, you will probably want to take at least some of the following steps: Firewalls Protect your computers from drive-by hacking by setting up a firewall on each of the wireless nodes. Router If you are using the wireless LAN to extend your Internet connection to another part of a building or an adjacent building, at least one node needs to provide the other wireless node(s) access to that connection. You can provide this access by turning on packet forwarding and configuring the computer as a router. Services Just as you would with any TCP/IP connection to a Linux computer, you can configure the services that are available to the wireless nodes. If you are using your wireless laptop to write a novel in the garden, you can configure the wireless computer in your house to act as a print server, file server, mail server, or other type of server (along with providing access to the Internet).
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Click the Devices tab. 3. Click the entry for your wireless card and select Edit. The Wireless Device Configuration window appears. 4. Click the Protocols tab. 5. Select TCP/IP and click Edit. The TCP/IP Settings window appears. 6. Enter the TCP/IP address for your wireless interface in one of two ways: Select “Automatically obtain IP address settings with” and select dhcp, bootp, dialup, or none. If you are using this selection, chances are you will be using DHCP to obtain your IP address and related IP information from a computer on your wireless LAN. Cross-Reference If you are using a Red Hat Linux system as a DHCP server, refer to Chapter 23 for information on configuring the DHCP server. Unselect “Automatically obtain…” and manually enter your IP address settings. Manually entering this information is a good idea if you are setting up a point-to-point wireless LAN (for example, between two wireless computers in adjacent rooms or buildings) in a private network. I used the addresses 172.31.0.10 on my laptop and 172.31.0.11 on my desktop computer. For the Subnet Mask, I used 255.255.0.0 (a class B private network address). On the laptop, I configured 172.31.0.11 as the gateway address, so the wired Ethernet card on my desktop computer can provide my route to the Internet. 7. Click OK to close the TCP/IP Settings window. 8. Click OK to close the Wireless Device Configuration window. 9. In the main Network Configuration window, click the DNS tab. 10. On the DNS tab, enter the information you need to identify your host name, domain name, and DNS servers (Primary, Secondary, and Tertiary). (If you are obtaining your IP address using DHCP, you may be receiving this information as well. If that is the case, you can skip this step). 11. Click Apply. 12. Click Close. When asked if you want to save changes, click Yes. Note On the computer that is acting as a gateway to your Internet connection, you need to turn on IP packet forwarding. Change the value of net.ipv4.ip_forward to 1 in the /etc/sysctl.conf file. Open that file as root user with any text editor and change the line as follows:
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Channel Choose a channel between 1 and 14. You can begin with channel 1. If you get interference on that channel, try changing to other channels. Transmit Rate Choose the rate of transmission from the following rates: 11M, 5.5M, 2M, 1M, or auto. Choosing auto (which is the default) allows the interface to automatically ramp down to lower speeds as needed. Lower speeds allow the interface to transmit greater distances and deal with noisy channels. Key You need the same encryption key for all wireless LAN cards that are communicating with each other. It is critical to get this value right. This key is used to encrypt all data transmitted and decrypt all data received on the wireless interface. Though you can leave the default key, you can ensure greater security by selecting a new key and entering it for the card on each wireless computer on your network. You can enter the number (up to ten digits) as XXXXXXXXXX or XXXX-XXXX-XX, replacing each X with a number. You can also enter fewer digits. For example, 99 would result in the number 9900-0000-00. Caution The encryption algorithm used with 802.11 networks is the Wired Equivalent Privacy (WEP) algorithm. Though using the encryption key is more secure than not using it, some experts feel that WEP has some inherent flaws that might allow a drive-by hacker to decrypt your wireless LAN traffic. For that reason, I strongly recommend using other techniques to protect your wireless LANs as well, such as firewalls and diligent log checking. See the Wireless Security sidebar for further information. 6. Click the General tab. The Nickname will probably be set to your host name. 7. Change the Nickname to an appropriate name for the interface. I change this value to the name of the interface, such as eth0, eth1, and so on. 8. Click OK on the Wireless Device Configuration window. 9. Click Apply on the Network Configuration window, and then click Close. You are asked if you want to save the changes. 10. Click Yes. Repeat this procedure for all wireless Linux computers on your LAN. In my case, I repeated the procedure for my second Red Hat Linux system. At this point, you can continue on to configure TCP/IP on your wireless interface. Configure TCP/IP To configure TCP/IP on your wireless LAN, you can use the same Network Configuration window you used for selecting the wireless options. 1. Open the Network Configuration window (as described in step 1 in the previous procedure). 2.
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To open the Network Configuration window from the GNOME menu, click Programs System Network Configuration. (Or, as root user, type neat& from a Terminal window.) The Network Configuration window appears. 2. Click the Devices tab. If your card was properly detected, you should see an entry for your wireless card. That entry should be of type “Wireless” and probably have a Nickname set as your host name. 3. Click the entry for your wireless card and select Edit. The Wireless Device Configuration window appears. 4. Click the Wireless Settings tab. The Wireless Device Configuration window should appear, as shown in Figure 25-4. Figure 25-4: Change wireless LAN settings from the Wireless Device Configuration window. 5. Change your wireless settings as appropriate. These are settings that are passed to the iwconfig command to set wireless extensions. Here are your options: ESSID (Network ID) The network name that identifies cells that are part of the same network. If you have a group of cells (which might include multiple nodes and repeaters among which a client could roam), this name can identify all of those cells as falling under one virtual network. Choose any name you like and then use that name for all computers in your virtual network. (ESSID stands for Extended Service Set ID.) Mode Indicates the mode of operation for the wireless LAN card. Because I am setting up a wireless LAN consisting of only one cell (in other words, no roaming to cells set up in other areas), I could set the mode to Ad hoc or simply leave it on Auto. Ad hoc mode allows the card to communicate directly with each of its peers. Managed mode can be used if you have multiple cells, requiring your card to communicate directly to an access point. You could also use Managed mode for a point-to-point network, such as when you use the wireless LAN to extend a network from one building to another. Frequency You can choose a particular frequency in which to transmit. No value is required, because selecting a channel implies a certain frequency. If you do enter a frequency, the value must be a number followed by a k (kilohertz), M (megahertz), or G (gigahertz). The default values for the channels you select range from 2.412G (channel 1) to 2.484G (channel 14), with other channels falling at .005 increments in between. The default is 2.422G.
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# /etc/init.d/pcmcia restart Shutting down PCMCIA services: cardmgr modules. Starting PCMCIA services: modules cardmgr. Check the /var/log/messages file. You should see some messages at or near the end of this file, describing what happened when the PCMCIA interface was shut down and restarted. If the card starts successfully, these messages will give you a wealth of information, such as the MAC address of the card, valid channels, and the interface that is associated with the card. Here are some examples: kernel: Linux Kernel Card Services 3.1.22 kernel: options: [pci] [cardbus] [pm] kernel: PCI: kernel: wvlan_cs: WaveLAN/IEEE PCMCIA driver v1.0.7 cardmgr[7707]: executing: ‘./network start eth0′ kernel: wvlan_cs: Registered netdevice eth0 kernel: wvlan_cs: Valid channels: 1 2 3 4 5 6 7 8 9 10 11 The previous output shows that the kernel recognizes the PCI card (at IRQ 11). The wvlan_cs module identifies the Orinoco card as a WaveLAN/IEEE Adapter in socket 0. The network script starts an Ethernet interface (eth0). Channels 1 11 can be used for wireless communications. If the wireless LAN interface started properly, you should be able to see the new interface using the ifconfig command, as follows: # ifconfig -a eth0 Link encap:Ethernet HWaddr 00:02:2D:2E:8C:A8 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:4 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 RX bytes:0 (0.0 b) TX bytes:272 (272.0 b) If your wireless LAN interface does not appear to be working, refer to the section Troubleshooting your Wireless LAN at the end of this chapter. If the interface seems to be working, you are ready to tune your wireless LAN card interface and set up TCP/IP to be able to use the interface. Configure wireless cards The Network Configuration window (neat command) the same window that you can use to configure regular wired Ethernet cards can be used to configure the basic options for your wireless LAN cards. Selections within this window let you: Select wireless options Select options that affect the wireless transmission. Configure TCP/IP Add information that allows the wireless transmission to be used to connect the computers to the Internet or other TCP/IP networks. The following sections describe how to use the Network Configuration window to set up your Wireless LAN. Parameter-setting methods that are not available through the Network Configuration window are described in the “Manually Configuring Wireless Cards” section. Likewise, if you don’t have a GNOME, KDE, or other desktop environment installed, skip to that section. Select wireless options To configure the basic options you need to get your wireless LAN working, open the Network Configuration window and edit the wireless interface that appears on the Devices tab. Follow this procedure: 1.
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needed, but I wanted to be able to use the GUI and various server features.) Because I was using the desktop computer as a gateway to the Internet, that computer also had a wired Ethernet card that was connected to my DSL modem to provide a route to the Internet for any computers on my wired or wireless networks. Insert wireless cards To physically install the wireless cards, follow the directions that come with the cards. For my laptop, I simply inserted one Orinoco card into a PCMCIA slot. For the desktop computer, I powered down, inserted the PCI adapter into a vacant slot, powered up, and inserted the other Orinoco PCMCIA card into the adapter. Load the modules The cardmgr daemon monitors the PCMCIA slots on computers that have them. If a card is recognized and listed in the PCMCIA database when the card is inserted, the appropriate module is loaded. You should also hear two beeps to indicate that the card has been recognized. On my laptop, my Orinoco wireless card was recognized and its modules loaded. On my desktop computer (with the PCI adapter), the card was not recognized, so I had to do some extra configuration. PCMCIA only To see what modules are loaded after a card is inserted on a computer that has only PCMCIA slots, type the lsmod command. In my example, because the Orinoco card uses the wvlan_cs module, output from the lsmod command includes the following lines: # lsmod wvlan_cs 23296 1 ds 7056 1 [wvlan_cs] pcmcia_core 41600 0 [wvlan_cs ds yenta_socket] You can see that the wvlan_cs module is loaded and that the referring modules include the ds module (PC Card Driver Services module) and pcmcia_core module. If you are using a different card, you may instead see one of the following modules: airo_cs, wavelan_cs, orinoco_cs, ray_cs, or netwave_cs. PCMCIA with adapter card If your computer has only ISA or PCI slots, you will need an adapter to use your PCMCIA wireless LAN card. When I installed a PCI adapter card, because Linux didn’t detect my card, the PCMCIA wireless LAN card wasn’t detected either. Therefore, I added the following lines to the /etc/sysconfig/pcmcia file so that the PCI adapter card would be recognized and the PCMCIA service would start automatically at boot time: PCMCIA=yes PCIC=i82365 The i82365 driver is a PCMCIA controller driver that includes the Yenta register specification. Yenta is used for CardBus bridges made by Cirrus Logic for a variety of manufacturers (Texas Instruments, IBM, Toshiba and others). The Orinoco PCI adapter was detected as a Texas Instruments PCI-1410 CardBus Controller. (To see the options available with the i82365 driver, type man i82365). Check that the cards are working If the modules have been loaded properly, the cardmgr should recognize each card and start up the Ethernet interface for it. To check that this happened, restart the interface as follows:
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Once you have established a wireless LAN interface, you can use a variety of Linux software to monitor and control access to that interface. For example, you can protect the interface by setting up the Linux system as a firewall, a proxy server, or a router. In other words, the wireless interface can be used in the same way you would use a wired Ethernet LAN interface. To use server and router features, you need to install the appropriate software packages as well. Setting Up a Wireless LAN Before you begin testing the distances you can obtain with your wireless Linux LAN, I recommend that you configure wireless cards on two computers that are within a few feet of each other. Once the two computers are communicating, you can change wireless settings to tune the connection and begin testing the transmission distances you can achieve. The text that follows describes the steps you need to take to set up a wireless LAN between two Linux systems. Although only two nodes are described, you can add more computers to your wireless once you know how. This procedure describes how to operate your wireless Linux LAN in two different modes: Ad hoc All of the computers in your wireless LAN are gathered into a single virtual network that is made up of only one cell. A single cell means that you cannot roam between different groups of wireless nodes and continue your communication invisibly. To do that requires a managed network. Managed As noted earlier, many wireless cards that are supported in Linux cannot operate as an access point. A Linux wireless card, however, can operate as a node in a managed network. The wireless configuration tools that come with Red Hat Linux let you identify the access point for Linux to use by indicating the access point’s MAC address. Choose equipment Start with two computers. You can add more computers later, once you understand how to get your wireless interfaces working. For this procedure, I used computers that had the following characteristics (you can use different computer and cards, if you like): Computers One computer was a laptop with an available PCMCIA slot; the other was a desktop system with only PCI slots. Wireless cards As mentioned earlier, I purchased two Agere (Lucent Technologies) Orinoco wireless LAN cards: one Gold Label and one Silver Label. For the desktop computer, I purchased a PCI adapter card because it had no PCMCIA slot in it. Both cards come with built-in antennas, so there was no need for additional antennas while I set up the two computers (in the same room) for wireless communication. Note The only difference between the Gold and Silver Label cards is support for more secure encryption on the Gold card, so there was no reason for me to choose two different types of cards. If I had it to do over again, I would have used two Silver cards and saved a few dollars. Red Hat Linux I installed Red Hat Linux on both machines, selecting a Laptop install for the laptop and an “Everything” install for the desktop computer. (The Everything install was not strictly
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Figure 25-3: Distance of obstructive objects from the wireless signal is called the clearance. Distance Although the actual distances that antennas can send and receive data varies greatly based on different factors, you can achieve distances of many miles with outdoor antennas. For example, two Orinoco 24 dBi directional parabolic grid antenna can theoretically achieve distances of up to 52 miles at an 11 Mbps transmission speed with a 180-meter clearance. Reduce that transmission rate to 1 Mbps and you can achieve distances of up to 149 miles with a 1200-meter clearance. Less expensive equipment, such as the Orinoco 14 dBi directional antenna (about $149), can achieve distances of up to 5.3 miles at 11 Mbps with a 13-meter clearance. Cable factor The distances that transmissions travel on the cables between the wireless cards and the antennas can impact the antenna you need. The shorter the cables, the greater the distances and speeds you will be able to achieve on your antenna. The power of an antenna is rated in terms of gain. Gain is measured in decibels, based on a theoretic isotropic radiator (or dBi). Higher gains offer opportunities for reaching greater distances at greater speeds. However, the ability of the antenna to focus that power (directional versus omnidirectional), greatly changes the speeds and distances that can be achieved. Installing Wireless Linux Software If you did a Laptop or an “Everything” installation of Red Hat Linux on your computer, the software packages needed to create your wireless LAN may already be installed. Drivers and modules needed to support PCMCIA cards and wireless cards should already be built into your Linux system. Besides the wireless drivers, the following software packages contain tools for configuring and working with your wireless LAN cards in Red Hat Linux: Kernel-pcmcia-cs Contains commands and configuration files to support PCMCIA cards. Included in the package is the wireless script (for starting the wireless LAN interface) and the wireless.opts file (sets default options for each type of wireless card). Wireless-tools Contains commands for setting extensions for your wireless LAN interface. Commands include iwconfig (for configuring your wireless interface) and iwlist (for listing wireless statistics).
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