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This chapter is from the book

Networking

Few modern computers are not on the Internet now. With such an important feature, having a networking problem can feel like a crippling blow, particularly for those of us who spend extended periods of time staring at a Web browser. This section identifies some of the common problems with wired and wireless networking.

I Can't Access My Wired Local Area Network

First, check that the cables for your network are plugged in correctly. On many hubs, a small light appears when a cable is plugged into one of the sockets. Many Ethernet cards also display a connection light.

Next, check whether the card has been recognized by the system. To find out, fire up the networking tool by clicking System > Administration > Networking, and you should see an icon displayed in the window that represents your network card. If there is no icon, your card has not been detected and loaded by Ubuntu.

In the networking tool, double-check that your settings are correct. You can check whether your network card is working and has an interface by opening a terminal with Applications > Accessories > Terminal and typing:

foo@bar:~$ ifconfig

You should see a number of blocks such as eth0 or ra0. One of these blocks should have a local IP address. The format of this address depends on which IP range is on your network. The range 192.168.0.n, where n is a number between 1 and 254, is commonly used. If you see an IP address in your ifconfig output, try pinging the IP address that you set as the gateway. If you did not set a gateway (typically when you obtain your IP address automatically with DHCP), your IP address is likely to be 192.168.0.1. Try to send packets to this IP address:

foo@bar:~$ ping 192.168.0.1

Change the IP address if your IP range is different. If you get a number of lines with a time = attribute at the end, your network card works.

If you have set up your network card to automatically grab an IP address with DHCP, you can get a new address by running the following command:

foo@bar:~$ sudo dhclient

My Computer Says It Can't Resolve a Web Site

If the network is working but Web sites are not loading, you might have a problem with the incorrect name or DNS servers, which turn domain names such as google.com into IP addresses. To test this, you will need to know an IP address. You may have been given some IP addresses for different services from your ISP. Alternatively, you can use another computer to find an IP address with which to test. Try pinging the address, and if you get pings back, you know it's a name server problem. To resolve this, specify the correct name servers in the DNS tab.

How Do I Use SSH for Transferring Files Across a Network?

Secure Shell (SSH) is a protocol for connecting to remote computers in a safe way. To connect on the client side to a remote computer, click Locations > Connect to Server, and choose SSH as the service type. In the first field, enter the hostname or IP address of the remote computer.

The folder field can be left blank but can be used to go straight into a folder when you open the connection in the file manager. For instance, the home folder of user joe is typically /home/joe. Other folders are still accessible by clicking the up button on the toolbar. Enter the username of the user on the remote computer in the username field. If it's the same as the local username, just leave it blank. Both the folder field and the username field are case sensitive. Click Connect to proceed.

The first time you connect, a question appears that says the identity of the remote computer is yet unknown. This is normal. Click the Login Anyway button to proceed. If you are asked for a password, enter the password of the user on the remote computer. Click on remember password for this session and Connect. If the password was wrong or it took too long to enter the password, it is asked again.

The connection appears on the desktop. If you chose not to remember the password for the session or in the key chain, you may be asked again. Now you can use the remote files the same way you use them locally. You can even copy files across different SSH connections and other network protocols such as FTP.

How Do I Use a Graphical Application Remotely with SSH?

To connect on the client side to the remote computer, first open a terminal. Click Applications > Utilities > Terminal. Now run this command:

foo@bar:~$ ssh host -X -l user

where user is the username on the remote computer, and host is the hostname or IP address. If the username is the same, leave out the -l user option. The -X option signals ssh that you want to run graphical applications. Make sure you use a capital X exactly as shown. Usernames are also case sensitive.

If it's the first time you are connecting, you will get a warning similar to the following:

The authenticity of host '251.152.123.101' (251.152.123.101)' can't
be established.
RSA key fingerprint is
01:12:23:34:45:56:67:78:89:9a:ab:bc:cd:de:ef:ff.
Are you sure you want to continue connecting (yes/no)?

Type yes, and press Enter. When asked for a password, enter the password of the user on the remote computer. Now you should have a shell on the remote computer, and it's possible to run commands remotely. For example, you can try Firefox to open up Mozilla Firefox, or Gaim to have a chat with yourself.

My Wireless Card Is Not Working

One of the greatest new features for laptop users in Ubuntu is Network Manager, an easy way to connect your Ubuntu system to any wireless network. Where previously you had to jump through hoops to do WPA or 802.1x authentication, Network Manager makes this completely transparent.

Simply click on the network icon in the upper panel by the clock to see all available wireless networks, and click on the network to connect to it. If wireless authentication is needed, be it WEP, WPA, or 802.1x, a dialog will pop up asking for your authentication details.

Of course, these improvements are not limited to laptop or even desktop users. Even for machines without a GUI, networking has been made easy by the Debian and Ubuntu developers who integrated WPA authentication into the standard network configuration system.

If Network Manager does not solve the problem, the first step should be to see which driver your wireless card needs. Do a search for your card on Google and in the Ubuntu forums to find out. Many of the drivers are already included in Ubuntu, but some newer drivers may not be present.

Next, you need to find out whether the driver is loaded. As an example, if you have an Intel Centrino and it uses the ipw2200 driver, run this command:

foo@bar:~$ sudo lsmod | grep ipw2200

Replace ipw2200 with the relevant driver for your card. If you get some lines returned, the driver is loaded and working. If nothing is returned, either your card is not supported or the driver is not included in Ubuntu. You should refer to the Ubuntu forums for further support.

With the card identified, you now need to get connected. The easiest way to do this is to select System > Administration > Networking. Inside this tool you should see an icon for your wireless card. Select it, and click the Properties button. Now add the name of the wireless network and a password if applicable. If you are using a normal password such as s3cr3tpass, select Plain (ASCII) from the Key box. If you are entering the long numeric password, use the Hexadecimal option.

If you are automatically assigned an IP address, use the Configuration box to select DHCP. Otherwise, select Static IP Address, and enter the details of your network in the boxes.

For more information, see https://wiki.ubuntu.com/HardwareSupportComponentsWirelessNetworkCards.

I Need to Use WPA or I Use WPA-PSK on My Wireless Access Point

To use WPA, you need a supported card. Such cards are listed on the WPA Supplicant Web site at http://hostap.epitest.fi/wpa_supplicant/. Common cards that support WPA under Ubuntu are various Broadcom, Atheros, and Intel chipsets.

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