Setting up an ISDN link

If you have an external ISDN TA then you need to check what type of beast it is. One sort you treat just like a serial modem, and they work OK with Linux - if you have a fast serial port (atleast 230,400bps if you wish to do MPPP). The other type needs a CAPI driver, so check there is a driver for Linux before you buy one.

Kernel versions 2.2.12 and up have ISDN driver support built in. On earlier versions you have to download some mods and patch the kernel - all good fun. Definite Linux 7.0 comes with kernel 2.2.12, so no problems in that area. These pre-compiled kernels load ISDN as a module. You will also need the isdn4k-utils package. These are available as RPM's.

NOTE: These scripts worked quite happily with 2.4.xx kernels.

The target is to get a system that will do 'dial on demand' - allow automatic dial out to your ISP for any system on the network. This also needs IP Masquerading. I have included that as part of the Firewall script.

I also show how to set-up a dial in link via ISDN. This requires the option files to be set-up in a particular way.

The advantage of using `dial-on-demand' is that any user can browse when they wish, without someone having to access the Linux machine to bring up the link. However, if you do not set up your Windows machines or Samba correctly then you may find lots of calls being made when you don't expect it. Mail clients like Outlook and Netscape have settings to check for new mail every so often. If you don't have a local e-mail server, then this will cause the link to come up. Disable this feature or set the time to a very long period. When Netscape is closed this may also cause a dial-out. Using a local cache (Squid) on your server, and pointing Netscape at that for its Internet connection can stop this.
Another cause of unwanted dial-outs is Windows browsing. See the Samba configuration page for a suggested set up.

Definite Linux provide a set of scripts called 'rh-isdn'. They don't seem to set up the routes correctly for my purposes. I have more experience with 'isdn4net', but they only assist with the set up of one interface, and we need at least two, one for dial-out to an ISP, and the other for incoming connections. Therefore I am using my own simple scripts based on the 'isdnctrl' facility provided by the isdn4k-utils package.

I am assuming that you have installed the card, and have Definite Linux 7.0 or later installed. (RedHat 6.0 or later with kernel 2.2.12 should do as well)

Make sure you have installed isdn4k-utils. To check do 'rpm -q isdn4k-utils'. It is provided on the Definite Linux or RedHat CDROM. It is usually necessary to be logged in as root to install an rpm package.

NOTE: It is not necessary to have an 'isdn' script run from /etc/rc.d/init.d with this method. The 'isdn4k-utils' package provides the executable files that are called by these scripts as required.

The other assumptions are that the Linux box is set to forward IP packets. Check that /etc/sysconfig/network has the line FORWARD_IPV4=true. You can set this by editing this file directly, or using a GUI method. Also any Windows machine must have the Gateway value in Network Neighbourhood - TCP/IP set to the IP address of your Linux machine. NOTE: These two steps are not necessary if you are only connecting a single Linux machine to the Internet.

To load the hisax driver module I use the following script.

The driver has been loaded!

If you use 'lsmod' you can see the modules that are loaded. There should be 'hisax', 'isdn' and 'slhc' amongst others.

The other Hisax card 'types' are as below

1 Teles 16.0
2 Teles 8.0
3 Teles 16.3 (non PnP)
4 Creatix/Teles PnP
5 AVM A1 (Fritz)
6 ELSA PCC/PCF cards
7 ELSA Quickstep 1000
8 Teles 16.3 PCMCIA
9 ITK ix1-micro Rev.2
10 ELSA PCMCIA
11 Eicon.Diehl Diva ISA PnP
11 Eicon.Diehl Diva PCI
12 ASUS COM ISDNLink
13 HFC-2BS0 based cards
14 Teles 16.3c PnP
15 Sedlbauer Speed Card
15 Sedlbauer PC/104
15 Sedlbauer Speed PCI
16 USR Sportster internal
17 MIC card
18 ELSA Quickstep 1000PCI
19 Compaq ISDN S0 ISA card
20 NETjet PCI card
21 Teles PCI
22 Sedlbauer Speed Star (PCMCIA)
24 Dr. Neuhaus Niccy PnP
24 Dr. Neuhaus Niccy PCI
25 Teles S0Box
26 AVM A1 PCMCIA (Fritz!)
27 AVM PnP (Fritz!PnP)
27 AVM PCI (Fritz!PCI)
28 Sedlbauer Speed Fax+
29 Siemens I-Surf 1.0
30 ACER P10
31 HST Saphir
32 Telekom A4T
33 Scitel Quadro
34 Gazel ISDN cards (ISA)
34 Gazel ISDN cards (PCI)
35 HFC 2BDS0 PCI
36 W6692 based PCI cards
37 HFC 2BDS0 S+, SP/PCMCIA

Edit /etc/isdn/isdn.conf. This file comes as part of isdn4k-utils. Enter the country code - UK is 44; the area prefix should be 0, and enter your own area code without the leading 0.

Now set-up the pap-secrets file. Edit /etc/ppp/pap-secrets.
Add a line -
'client'   'server'   'secret'
where
'client' is your account or login name with your ISP
'server' - just use *
'secret' is the password for your ISP account. Don't include the quote marks.

Isdnctrl

The first script is used with Demon Internet. They use 'static IP numbers' and you have to define the IP numbers to be used in your scripts.

Do not run this script yet as the option files have not been defined.

NOTE: You may find ipppd in /sbin or /usr/sbin depending on your version of isdn4linux etc. Use 'whereis ipppd' to find out.

Setting up the `ioptions' files

The `ippp0' interface is added in the script above. Type `ifconfig' and you should see the interface details.
I will concentrate on the option files necessary to bring up the link to Demon Internet. Later I will cover accessing an ISP using dynamice IP's.

Create `/etc/ppp/ioptions'. It should contain -

NOTE: The lines -vj, -ac -pc, etc disable various compression options. Using no compression has given the most reliable connection with some versions of isdn4k-utils, but it is worth checking with newer versions to see if compression options are now available.

Now create a script to remove the ISDN set-up.

Make this executable.

We have now created -
1) a script to load the hisax driver - `loadhisax'
2) a script to setup the ippp0 interface and isdnctrl parameters for ippp0 - `isdnup'
3) the option files to be used by `ipppd' - `/etc/ppp/ioptions' and `/etc/ppp/ioptions.ippp0'
4) and a script to remove this set-up - `isdndown'

Fiddly bits

The routes direct the IP traffic to the correct place. For `dial-on-demand' you must have the default route set to ippp0 before the link comes up or nothing happens. We have added a default route as the last line of the `isdnup' script. However, once the link is up, this route goes away and other routes are added!!. Make sure you have only one default route. You can see this problem being discussed frequently on the isdn4linux newsgroup `de.alt.comp.isdn4linux', and in the FAQ that comes with isdn4linux.

My solution is to use /etc/ppp/ip-up.local, and /etc/ppp/ip-down.local. The ip-up.local script should be called from ip-up after the link to your ISP is brought up, whereas the ip-down.local script is called by ip-down when the link dies.

These files don't always exist, so create them. They must be executable, and have #!/bin/bash as the first line. (Yes, you must include the #)

Edit /etc/ppp/ip-up.local to include -

Because this script is run whenever the link is brought up using any of the interfaces, it is important to only add the default route for the interface that requires it. The ip-up.local and ip-down.local scripts are passed certain parameters when they are called. The first parameter is the interface. This script tests for ippp0 and only adds a default route if that is true. Make sure there are spaces either side of the square brackets and the = sign. These scripts do not have any knowledge of your path, so include the full path to the command. See `man ipppd' for more details.

When the link is disconnected you must remove the routes that were added when the link came up, otherwise the system will not be in the correct state to initiate the link again.

Edit /etc/ppp/ip-down.local to include -

NOTE: Do make sure that when the link comes up you have only one default route.

To initiate the link

If `isdnctrl dialmode ippp0' is set to manual, type `isdnctrl dial ippp0', and the system will dial the number defined in the `isdnctrl addphone' statement.
To bring the link down use `isdnctrl hangup ippp0'.

Do make sure you have the IP numbers for your ISP's nameservers in /etc/resolv.conf.

Using ISDN and a dynamic IP

The script /root/bin/isdnup changes slightly.

The /etc/ppp/ioptions.ippp0 will change as below -

You should now be able to access an ISP who uses dynamic IP numbers.

NOTE: If you wish to use a firewall with a dynamic IP, add the firewall rules to the ip-up.local file. See our Firewall page for more details
Also if you need to use CHAP authentication, which I understand is required by BTInternet, change the 'user xxx' above to 'name xxx' .

Dial in configuration

Set up ippp1 on the system that will answer the dial-in request. In this set-up the server allocates the IP number to be used by the remote user, so use a 'dynamic-IP' configuration on the remote system.

Create a file /root/bin/isdndialin.up -

The isdnctrl eaz option is interesting. For EAZ read MSN (Multi Subscriber Numbering). This is your local digital number. On BT Business Highway, I have found using the last 6 digits of our digital number works, even though BT say it should be 0. On an ISDN exchange using the last three digits of the number works (the extension no: perhaps). I think it is due to the checks carried out by isdn4linux. If you have problems try other options, unless you know the real MSN when use that. If you haven't set-up /etc/isdn/isdn.conf correctly then this will not work
NOTE: MSN is not available with Home Highway.

The /etc/ppp/ioptions file containing the common values will be read when ippp0 comes up for dial out to your ISP, and when ippp1 comes up for dial-in, so options specific to ippp1 are put in /etc/ppp/ioptions.ippp1.

Make this script executable. Type 'isdndialin.up' start, and 'isdndialin-down' to disable.

NOTE: It is important to add some additional lines to /etc/ppp/ip-down.local to sort out the routes after the script has been run.
Add :

Loading ISDN on boot-up

For other Linux distributions, add the same lines to the relevant start-up file.

MPPP - Multi PPP or Channel Bundling.

Both the options file and the script containing all the isdnctrl commands need changing.

I have called the new file 'isdnMPPP.up'. The original 'isdndown' file removes the interface.

The options file '/etc/ppp/ioptions.ipppM' is as follows:

PLEASE NOTE. I have not tested the MPPP set up very much, so if you find any improvements please let me know.
This configuration now seems to work well with Demon, on a regular basis. Happy browsing!