Chipset revealed

Using the command 'lsmod', you can see what modules are already loaded.

Here is output from lsmod on my sample system

# lsmod
Module                  Size  Used by    Not tainted
sd_mod                 10316   0 (autoclean) (unused)
scsi_mod               86068   1 (autoclean) [sd_mod]
i2c-dev                 3492   0 (unused)
i2c-core               12228   0 [i2c-dev]
ipt_state                504   3 (autoclean)
ip_conntrack           19044   0 (autoclean) [ipt_state]
iptable_filter          1644   1 (autoclean)
ip_tables              11776   2 [ipt_state iptable_filter]
8139too                12776   1
crc32                   2848   0 [tulip 8139too]
eepro100               18548   1
mii                     2144   0 [8139too eepro100]
raid1                  12688   3

To load the 'tulip' module, type the command 'modprobe tulip'. In classic UNIX fashion, this command gives no feedback if it works, only if it fails.

Trying to load a module for which there is no network card installed does not hurt anything (in my experience). Modprobe will load the module, the module will look for hardware, and if it does not find anything it will exit with an error like "init_module: No such device".

Success just gives you another command line prompt, but some useful output will be written to the kernel log file, which you can list by typing 'dmesg'; the last few lines of output are the interesting ones; on my system after loading the tulip driver I see this:

Linux Tulip driver version 0.9.15-pre12 (Aug 9, 2002)
PCI: Found IRQ 10 for device 00:0e.0
tulip0:  MII transceiver #1 config 3100 status 7849 advertising 05e1.
tulip0:  MII transceiver #2 config 1000 status 7849 advertising 05e1.
tulip0:  MII transceiver #3 config 1000 status 7849 advertising 05e1.
tulip0:  MII transceiver #4 config 1000 status 7849 advertising 05e1.
eth1: ADMtek Comet rev 17 at 0xf800, 00:02:2A:B8:23:D7, IRQ 10.

The first line identifies the module itself and the subsequent ones are the output it generated as it probed for ethernet cards and initialized itself. The good news is the line starting with 'eth1'. This means the card is now available as network device /dev/eth1. Success!

Once you have figured out which driver you need to have loaded, you have to arrange for it to load every time it is needed after you reboot the system. You do this by adding line(s) to the modprobe configuration file (Alas, this config file goes by different names on different distributions and sometimes even different releases of the same distro. A common name is /etc/modprobe.conf, and /etc/modules.conf is another one. On Debian-based systems, look in the /etc/modutils/ directory.)

In my example, I'd see the eepro100 line for the Intel EtherPro card and add another after it, like this:

alias eth0 eepro100
alias eth1 tulip

Each 'alias' line associates a device (in this case /dev/eth0 and /dev/eth1) with a particular driver, so that when the system tries to configure a given device using its device name, the module system will be able to automatically find the right driver and load it.

Using the module loader, on reboot the system won't automatically load the unless you reference it from your network configuration. That's your next step. (You can force loading of modules at boot but that is another story. You don't need to do that for network drivers.)

Now we configure the network interface

Now that you have configured your system to load the right driver for your card, you have to configure the network interface.

Distros vary a lot in how they support configuration of a network interface. Most have some kind of text- or desktop-based control panel for doing network configuration. But again, it's more instructive to lift the hood and look inside. If you learn what's going on inside, you can debug the system much more easily.

In your case you are adding a second interface using another DSL line, so what you want to do is copy the existing setup for the first interface and then edit it.

The systems that I have worked with fall into two camps, Redhat and Debian.

Redhat-like systems

This includes Mandriva and Trustix, among others. SuSe is similar.

The Redhat (and similar) systems keep things in /etc/sysconfig. The 'network' file defines the primary interface and gateway (usually Internet router). Then in /etc/sysconfig/network-scripts, you will find an individual file for each interface. As a starting point I'd suggest not touching /etc/sysconfig/network. Go into /etc/sysconfig/network-scripts and copy the eth0 file, and edit it to support your new interface. (SuSE uses the same idea but files are moved around. Can't have things to simple.)

This is what a typical network file looks like:

# cd /etc/sysconfig
# cat network
NETWORKING=yes
HOSTNAME=mercury.mydomain.com
NOZEROCONF=yes
GATEWAYDEV=eth0
GATEWAY=66.224.50.232

Here are commands to create and edit the file for your new interface:

cd /etc/sysconfig/network-scripts
cp ifcfg-eth0 ifcfg-eth1 # Copy the existing interface config file
gedit ifcfg-eth1         # (or use whatever text editor you want)

You have to change the file as appropriate for your needs; in your case, using a second DSL line, the interface should be able to get an IP address from the DSL gateway, so you can leave it set to dynamic addressing.

DEVICE=eth0	         # All I'd have to do is change this line to read "eth1"
BOOTPROTO=dhcp
ONBOOT=yes

Debian-based

This includes Ubuntu, which is the desktop software I am using right now.

Debian-based systems keep all the networking settings in files in the directory /etc/network/. You will want to edit the interfaces file, and add a new block there to describe the new interface.

These are the commands to edit the file...

# cd /etc/network
# gedit interfaces

...and these are the lines in the file

# The primary network interface
iface eth0 inet dhcp

# Added these lines to activate second network interface on 20 Feb 2006
iface eth1 inet dhcp
 

Activating the new interface

Turning on and off just the new interface can be done with 'ifup eth1' and 'ifdown eth1' respectively. Output from these commands varies on different distros; mine gives lots of feedback, some give none. Either way after running either command, you can look at the current settings by running the command 'ifconfig eth1'. You will want to make sure the interface got an IP address from the DSL router after running 'ifup', so look for the 'inet addr' line. If the address line is missing, DHCP failed. Check cabling and make sure your new DSL provider actually uses DHCP to provide the address. More details than this are really beyond the scope of this column. See the resources section below for more info.

Here is the output for a functioning interface.

# ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 00:04:75:C1:CB:4A
          inet addr:192.168.123.247  Bcast:192.168.123.255  Mask:255.255.255.0
          inet6 addr: fe80::204:75ff:fec1:cb4a/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1749454 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1185618 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1660257798 (1.5 GiB)  TX bytes:364994034 (348.0 MiB)
          Interrupt:11 Base address:0x1000