Help with Linux Networking

This page is intended to be a consolidated resource of all things pertaining to networking your Linux laptop. It is assumed that you have an IBM Thinkpad T43 with Suse 10 Linux (running KDE), as imaged by Brad Tufts and Tim Riker.

How it works

Your laptop's OS is set up to use the following network interfaces:

Every linux distribution does the following items differently. Even in suse 10, this is not uniform. The following is how we are set up:

On boot, in the kernel load, suse can be set up to load modules in a fixed order (to set this, edit, as root, /etc/sysconfig/kernel and edit this line MODULES_LOADED_ON_BOOT="tg3 nvram"). This is recommended.

At any rate, the modules for the network interfaces are loaded into the OS. While executing the bootup scripts, suse looks at all files matching /etc/sysconfig/network/ifcfg-*. Each of these files relates to a network interface. This is what connects the module to the specific network interface. In these files, the line STARTMODE determines how the interfaces are started. If they are all set to manual, then nothing will automatically be launched on boot (it may be a good idea to start at this point).

Comands and Tools

Command line

GUI

Connecting at work

Land-line

Down your wireless interface, if it's not already (ifconfig and look for an entry for wlan0). If it's up, disconnect the VPN, then down it with sudo ifdown wlan0.

Assuming you have your network interfaces available, but down, make sure you are plugged into the network, open a shell and run

sudo ifup eth0

Use the command ifconfig to check the status. Check its output to see what IP address your laptop was assigned for interface eth0.

Alternately, run kinternet, right-click to make sure that the eth0 interface is selected, then choose dial in.

Wireless

Down your land-line interface, if it's not already (ifconfig and look for an entry for eth0). If it's up, down it with sudo ifdown eth0.

Assuming you have your network interfaces available, but down, run

sudo ifup wlan0

Use the command ifconfig to check the status. Check its output to see what IP address your laptop was assigned for interface wlan0. It might take a few moments, so if the IP doesn't show up immedaitely, wait ten seconds and try again.

Alternately, run kinternet, right-click to make sure that the wlan0 interface is selected, then choose dial in.

Once you have an IP address, you need to connect to the VPN (described below).

Connecting at home

Land-line

Follow the same instructions for connecting to a home network as for the office network, assuming you have something serving DHCP to give you an IP address. Until you connect to the VPN, you will need to set your browser's proxy to "direct connect", as you can't see the proxy servers at work.

Once you have an IP address, you need to connect to the VPN (described below).

Wireless

The file /etc/sysconfig/network/ifcfg-wlanxxxxxxx contains settings for the wireless connection here in the office. You will likely need a different configuration for home use. Probably the best way to accomplish this is to move that file out of the way (rename it to something that doesn't start with ifcfg so that the system won't find it), and use YaST2 to create another one (K-Menu then control center then YaST2 Modules then Network Devices then Network Card (enter Administrator Mode using the button at the bottom), then configure your wireless card to connect to your home wireless network. Once you're done, you can move that generated file out of the way, and replace it with the work one, for connecting at work.

I wrote a one-line script that copies the appropriate file onto the one that the system is looking for, so I can easily switch between work and home wireless networks.

Once you have an IP address, you need to connect to the VPN (described below).

Sprint air-card

To set this up the first time only, do the following:

1. Plug the air-card into the lower PCMCIA slot.
2. add this line to /etc/init.d/boot.local: modprobe usbserial vendor=0x1410 product=0x1110
3. Using yast, configure the modem, as follows
   • Network devices | modem
   • Add a new modem
     • modem device: /dev/ttyUSB0
     • custom provider
       • provider name: Sprint
       • phone number: #777
       • user name: "user"
       • password: "password"
       • uncheck box "always ask for password"
     • next
     • finish
4. edit /etc/sysconfig/network/ifcfg-modem0 and add PPPD_OPTIONS='lcp-echo-interval 0'
5. reboot (or better yet just run rmmod usbserial then /etc/init.d/boot.local)

Once it has been configured, do the following to bring it up (check ifconfig until you get an IP address, it can take a little while, and the modem0 interface won't show up at first; just be patient and try it every few seconds):

sudo ifup modem0

Of course, once you connect to the internet using the air card, you still need to connect to the VPN, as described below.

And this will bring it down:

sudo ifdown modem0

For reference, here is the block of configuration code from /proc/bus/usb/devices that is being used:

T:  Bus=06 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=12  MxCh= 0
D:  Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=1410 ProdID=1110 Rev= 0.00
S:  Manufacturer=Novatel Wireless Inc.
S:  Product=Novatel Wireless Merlin CDMA
C:* #Ifs= 2 Cfg#= 1 Atr=a0 MxPwr=100mA
I:  If#= 0 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=ff Prot=ff Driver=airprime
E:  Ad=81(I) Atr=03(Int.) MxPS=  16 Ivl=128ms
E:  Ad=82(I) Atr=02(Bulk) MxPS=  64 Ivl=0ms
E:  Ad=02(O) Atr=02(Bulk) MxPS=  64 Ivl=0ms
I:  If#= 1 Alt= 0 #EPs= 2 Cls=ff(vend.) Sub=ff Prot=ff Driver=airprime
E:  Ad=84(I) Atr=02(Bulk) MxPS=  64 Ivl=0ms
E:  Ad=04(O) Atr=02(Bulk) MxPS=  64 Ivl=0ms

Sprint Air-Card Alternate Configuration

For some users, the above instructions don't work outside the valley. Alternately, you may need to do the following:

1. complete "first time only" steps as above
2. download and install kppp from suse
3. set the following in kppp settings: lcp-echo-failure 9999
4. run kppp, connect from gui and then run vpn

VPN Connection

KNOWN ISSUE Some people have reported a problem with accessing the web via the VPN from home. See Linux Image Issues, the section on VPN.

There are two ways to connect to the VPN, one using the GUI program KVpnc, the other using a command line program, vpnc.

KVpnc

The GUI method is always very slow to connect, and sometimes doesn't work. Run the KVpnc program and connect to the VPN. This step can take more than 60 seconds, after you click the connect button, until it reports you are connected.

vpnc

You need to edit (as root) the file /etc/vpnc/onlyDevNet2.conf. Comment out the NO DISCONNECT line, and uncomment out the lines for username and password. Put in your groupwise username and password here.

To connect, use this command:

sudo vpnc onlyDevNet2.conf

To disconnect, use this command:

sudo vpnc-disconnect

Settings

For reference, here are the settings needed to connect to the office VPN:

ESSID (called Network name in the kwifimanager tool): chq-v601
Operation mode: managed
speed: auto
Using encryption. Key: 01234567890123456789012345 (as hex)

Safety when using SSH

If you regularly ssh into other boxen, be careful with your use of commands like sudo ifdown eth0. Accidentally typing this into a console that is attached to another box can have disastrous consequences. After doing this once, I wrote a set of scripts to use on my laptop, eliminating the risk. I put the following files, with the following contents, into my bin directory (yours should be on your path), and did chmod +x XXXX for each file.

Extreme measures

Other things to try, if things aren't going well.

• rmmod tg3 will remove the module from the OS, and modprobe tg3 will put it back. Use with caution, when you have an interface that just won't go down.