In order to use PPP, your Linux kernel must be compiled to include PPP
support. Obtain the Linux source code for your kernel if you do not
already have this - it belongs in /usr/src/linux on Linux's standard
file system.
Check out this directory - many Linux distributions install the source tree (the files and subdirectories) as part of their installation process.
Linux kernel sources can be obtained by ftp from sunsite.unc.edu or its
mirror sites.
The following are brief instructions for obtaining and installing the Linux kernel sources. Full information can be obtained from The Linux Kernel HOWTO.
In order to install and compile the Linux kernel, you need to be logged in as root.
/usr/src directorycd /usr/src/usr/src/linux to see if you already have the
sources installed./usr/src.rm -rf /usr/src/linuxtar xzf linux-2.0.6.tar.gzcd /usr/src/linux and read the README file. This contains
an excellent explanation of how to go about configuring and compiling a
new kernel. Read this file (it's a good idea to print it out and have a
copy handy whilst you are compiling until you have done this enough
times to know your way around).You MUST know what cards/devices you have inside your PC if you are going to recompile your kernel!!! For some devices (such as sound cards) you will also need to know various settings (such as IRQ's, I/O addresses and such).
To start the configuration process, follow the instructions in the README file to properly install the sources. You start the kernel configuration process with
make config
In order to use PPP, you must configure the kernel to include PPP support (PPP requires BOTH pppd AND kernel support for PPP).
PPP (point-to-point) support (CONFIG_PPP) [n] y
Answer the other make config questions according to the hardware in your PC and the features of the Linux operating system you want. Then continue to follow the README to compile and install your new kernel.
The 1.2.13 kernel creates only 4 PPP devices. For multi- port serial cards, you will need to edit the kernel PPP sources to obtain more ports. (See the README.linux file that comes as part of the PPP-2.1.2 distribution for full details of the simple edits you need to make).
Note: the 1.2.13 configuration dialogue does NOT allow you to go
backwards - so if you make a mistake in answering one of the questions
in the make config dialogue, exit by typing CTRL C and start again.
For Linux 2.0.x, you can use a similar process as for Linux 1.2.13. Again, follow the instructions in the README file to properly install the sources. You start the kernel configuration process with
make config
However, you also have the choice of
make menuconfig
This provides a menu based configuration system with online help that allows you to jump around in the configuration process.
There is also a highly recommended X windows based configuration interface
make xconfig
You can compile PPP support directly into your kernel or as a loadable module. If you only use PPP some of the time that your Linux machine is operating, then compiling PPP support as a loadable module is recommended. Using 'kerneld', your kernel will automatically load the module(s) required to provide PPP support when you start your PPP link process. This saves valuable memory space: no part of the kernel can be swapped out of memory, but loadable modules are automatically removed if they are not in use.
To do this, you need to enable loadable module support:-
Enable loadable module support (CONFIG_MODULES) [Y/n/?] y
To add PPP kernel support, answer the following question:-
PPP (point-to-point) support (CONFIG_PPP) [M/n/y/?]
For a PPP loadable module, answer M, otherwise for PPP compiled in as part of the kernel, answer Y.
Unlike kernel 1.2.13, kernel 2.0.x creates PPP devices on the fly as needed and it is not necessary to hack the sources to increase available PPP device numbers at all.
/proc/net/devIf you are using PPP-2.2, you will find that a side effect of the 'on
the fly' creation of the ppp devices is that no devices show up if you
look in the /proc/net file system until a device is created by
starting up pppd:-
[hartr@archenland hartr]$ cat /proc/net/dev
Inter-| Receive | Transmit
face |packets errs drop fifo frame|packets errs drop fifo colls carrier
lo: 92792 0 0 0 0 92792 0 0 0 0 0
eth0: 621737 13 13 0 23 501621 0 0 0 1309 0
Once you have one (or more) ppp services started, you will see entries such as this (from our ppp server):-
[root@kepler contrib]# cat /proc/net/dev
Inter-| Receive | Transmit
face |packets errs drop fifo frame|packets errs drop fifo colls carrier
lo: 428021 0 0 0 0 428021 0 0 0 0 0
eth0:4788257 648 648 319 650 1423836 0 0 0 4623 5
ppp0: 2103 3 3 0 0 2017 0 0 0 0 0
ppp1: 10008 0 0 0 0 8782 0 0 0 0 0
ppp2: 305 0 0 0 0 297 0 0 0 0 0
ppp3: 6720 7 7 0 0 7498 0 0 0 0 0
ppp4: 118231 725 725 0 0 117791 0 0 0 0 0
ppp5: 38915 5 5 0 0 28309 0 0 0 0 0
If you are setting up your Linux PC as a PPP server, you must compile in IP forwarding support. This is also necessary if you want to use Linux to link to LANs together or your LAN to the Internet.
If you are linking a LAN to the Internet (or linking together two LANs), you should be concerned about security. Adding support for IP firewalls to the kernel is probably a MUST!
You will also need this if you want to use IP masquerade to connect a LAN that uses any of the above mentioned 'unconnected' IP network numbers.
Once you have installed and rebooted your new kernel, you can start configuring and testing your PPP link(s).