		Sane Hotplug network interface management
		-----------------------------------------

INTRODUCTION
------------
	In the old day, all Wireless cards were managed by the
excellent Pcmcia subsystem and its rich configuration scripts, and
life was happy. Then came the wireless PCI cards, then the wireless
USB dongles. Some unification was needed, and rather than adapt the
Pcmcia subsystem for PCI and USB, it was decided to create the much
simpler Hotplug systems.
	The USB subsystem already use Hotplug, and the Pcmcia
subsystem is migrating to it, CardBus cards (32 bits) already use
Hotplug, whereas Pcmcia cards (16 bits) still use the old Pcmcia
scripts.
	The Hotplug system is still in its infancy, but already show
some good promises. Most users are disapointed at first by its
apparent lack of features compared to the Pcmcia scripts. In this
document, we will show how to fully exploit the Hotplug system and try
to implement the equivalent of all the functionality of the Pcmcia
scripts.

ASSUMPTIONS
-----------
	The target audience of this document is mostly power users and
distribution maintainers, but it should give enough clues to help
newbies. You should have read and understood DISTRIBUTIONS.txt. The
procedures described here are more advanced than the simple
configuration described in DISTRIBUTIONS.txt.
	The main focus is of course removable wireless interfaces, but
we will try to keep things generic and talk of the whole network
interface management, so this should apply also to built-in Ethernet
cards.

PROBLEM STATEMENT
-----------------
	Let assume a Linux system and two or more network devices,
Device A and Device B. Those devices may be built-in or removable,
they may be present or absent from the system at any time, and
activated in any particular order.
	The user wants to assign Configuration A to Device A and
Configuration B to Device B, without the possibility that Device A get
assigned Configuration B.
	Different users may have different definition of what is
Device A. For some, it's a specific instance of a specific hardware,
for others any hardware that meet some criteria (a wireless card, an
Ethernet card).
	The user may also want to have multiple configurations
depending on various factors (like the old Pcmcia schemes). Device A
may get Configuration A1 or Configuration A2 depending on those
factors.
	By default, all network interfaces are created using a default
interface name (starting at "eth0" and going up). I call that problem
"all my cards are eth0". And by default, "eth0" point to a single
fixed configuration in the configuration database. Clearly, this won't
satisfy our requirements.

EXAMPLE SYSTEM
--------------
	The distribution I use is Debian 3.0, and some parts will be
specific to it. However, it should be easy to translate to other
distributions and I welcome additions to this document.

	The example system is as follows :
		o Linux 2.6.X SMP kernel with hotplug support
		o Fully modular system (all network drivers as modules)
		o PCI Ethernet card : AMD PCnet LANCE (pcnet32 - eth4)
		o PCI Ethernet card : HP 100VG J2585B (hp100 - eth2)
		o ISA Wireless card : Old AT&T Wavelan (wavelan - eth3)
		o ISA-Pcmcia bridge : VADEM VG-469 (i82365 - slot 0)
		o PCI-CardBus bridge : Ricoh RL5c475 (yenta_socket - slot 2)
		o Pcmcia 802.11 card : Aironet 350 (airo_cs - eth0)
		o Pcmcia 802.11 card : Lucent Orinoco (orinoco_cs - eth0)
		o CardBus 802.11 card : SMC 2835W (prism54 - prism0)

	This system just happen to be my Linux development box, and
has enough interfaces to make it interesting. All the example I quote
in this document are extracted from this fully working system.

BASIC CONCEPTS
--------------
	Most of the concept and tricks presented here are not really
new, the main contribution is to integrate them together and make them
work.

	1) Removable network interfaces are managed by Hotplug
(Pcmcia, CardBus, USB...). We can't assume that those interfaces are
always present in this system and available at boot time (Pcmcia cards
are not made to be soldered in the Pcmcia slot), therefore Hotplug is
the only way to go.
	2) Built-in PCI and ISA cards are managed by the init scripts,
like they have always been. The ISA subsystem will never have Hotplug
support, and hotplug is not necessary for PCI cards.
	3) Built-in devices that are disable most of the time should
be enabled manually.
	4) (1), (2) and (3) must be compatible on the same system and
play nice with each other.

	5) A well defined and consistent network interface name is
assigned to each network hardware interface using 'ifrename'. Device A
is always named 'ethA' (or whatever name you like such as
'mynetworkcard').
	6) No interface is called 'eth0' (or 'wlan0'). Any unknown
device would be 'eth0', thefore known device should avoid using it
because it might be already taken.
	7) Multiple configurations for a single interface (schemes)
are managed by the ifup/ifdown subsystem.

CONFIGURATION FROM INIT SCRIPTS
-------------------------------
	It may seems paradoxal, but before setting up Hotplug, we need
to make sure that the initialisation of network cards via init
scripts is done properly and doesn't get in our way.
	The configuration of network cards via init scripts is the
traditional way network is initialised in Linux. The advantage of this
method is that it's very well documented and understood, and has not
changed much over the years. Unfortunately, it doesn't support
properly removable cards.
	The init scripts perform the following 3 functions in that
order :
		1) load necessary driver modules
		2) rename interface to name chosen by the user
		3) configure those interfaces

	1) Applicability
	----------------
	Configuration from init scripts is applicable to any built-in
network interface (ISA, PCI...), i.e. interfaces availalble at boot
time and that will never be removed from the system.
	The Hotplug subsystem has also the ability to configure some
of the built-in network interfaces, such as PCI cards. However, there
is a class of devices that will never have Hotplug support, such as
ISA and EISA cards, and for those Hotplug won't work.
	The advantage of using the init script method is that you are
probably already familiar with it and you have the ability to select
which interfaces should be configured at boot and which interface
should only be enabled manually (whereas Hotplug just configures
everything).

	2) Loading driver modules (if/as needed)
	----------------------------------------
	Most distributions build the kernel drivers as modules. This
modular setup allow to minimise the amount of memory used by the
system and the flexible loading/unloading of drivers.
	You can also compile your kernel with static drivers
(non-modular). In that case, the driver will always be available in
your kernel, you don't need to configure the module subsystem, so you
can skip directly to the next section.

	There are 3 alternatives to manage device drivers as
modules. Some distribution have explicit list of modules that are
loaded at boot time, if you want to use that feature you need to check
your distribution. Some system, such as hotplug or kudzu, can scan the
various buses of the PC and load the appropriate drivers, and this is
mostly configuration-free, but may not support all devices. The module
subsystem also allow to load modules 'on-demand'.

	I personally prefer to use the 'on-demand' feature of the
module subsystem has, as it allows you to not have to specify the list
of modules that need to be loaded, and only modules really necessary
are loaded which save kernel memory. You can also choose which module
to load when there are multiple altenate modules valid for your
hardware (which happens quite often).

	With kernel 2.6.X, the module subsystem is configured in
/etc/modprobe.conf. To configure 'on-demand' module loading, I need to
add to this file the following lines :

--------- /etc/modprobe.conf ----------------
# HP 100VG J2585B PCI card
alias eth2 hp100

# AMD AMD PCnet LANCE PCI card
alias eth4 pcnet32

# Old AT&T Wavelan ISA card
alias eth3 wavelan
options wavelan io=0x390 irq=15
---------------------------------------------

	Your distribution may already have lines for your interfaces,
either replace them or make sure they are correct (some distro are
notorious for picking the wrong driver name). This file also contains
configuration for lot of other subsystems, obviously you don't want to
touch that.
	In this file, you put the name you would like the interface to
have (we'll fix that in a minute). You note that for modern PCI cards,
this is much more straightforward than for old ISA cards.

	3) Installing 'ifrename'
	------------------------
	You will need to install ifrename on your system. 'ifrename'
is part of the Wireless Tools package (version 27 and later) and is a
complete rewrite of the now obsolete 'nameif'.
	Some distributions, such as Debian Sarge, offer a specific
package for 'ifrename', and in this case you should just install this
package. Other distributions may include ifrename as part of their
'wireless tools' package (this should be the case for Geentoo and
Mandrake). Other distributions, such as Debian 3.0, don't include
ifrename at all, and you should compile yourself a recent version of
Wireless Tools (v27 or later) and install it.

	In any case, you should verify if 'ifrename' is properly
installed, and what is the path to call it.
--------------------------
> which ifrename
/sbin/ifrename
--------------------------
	Most distributions will install 'ifrename' in '/sbin', while if
you compile your own wireless tools, it will be in '/usr/local/sbin'.

	4) Making the boot scripts call 'ifrename'
	------------------------------------------
	You need to make sure 'ifrename' is run at boot time. Most
distributions don't do that yet by default.
	This is a part that is distribution specific, so you will need
to look into your init files. It will need to run just before the call
to 'ifup' or 'ifconfig' command.

	In Debian 3.0, it needs to be run from /etc/init.d/networking,
which is not the default. The necessary patch is below :

----------------------------------------------------------------
--- networking-orig     Wed Feb 18 13:56:23 2004
+++ networking  Fri Feb 20 14:51:06 2004
@@ -120,6 +120,15 @@ case "$1" in
         doopt syncookies no
         doopt ip_forward no
 
+       # Optionally remap interface names based on MAC address.
+       # '/sbin/ifrename' is part of wireless-tools package.
+       # /etc/iftab is currently not created by default. Jean II
+       if [ -x /sbin/ifrename ] && [ -r /etc/iftab ]; then
+           echo -n "Remapping network interfaces name: "
+           ifrename -p
+           echo "done."
+       fi
+
         echo -n "Configuring network interfaces: "
         ifup -a
        echo "done."
----------------------------------------------------------------
	Don't forget to set the appropriate path to call ifrename (see
step (3) above).

	You may want to also set the proper options for ifrename
(check the man page).
	The option '-p' enable module autoloading compatibility.
	The default version of 'ifrename' also includes some specific
Debian support : using "ifrename -p -d", only the proper modules are
loaded. If you are using Debian, you should use this option.

	5) Renaming interfaces
	----------------------
	As stated above, we use 'ifrename' to assign names to
interfaces.

	First, you need to get the MAC address of each of you
interface. You can read it on the label on the card or display it
using the 'ifconfig' command. Remember that the interface won't load
yet with the proper name, so you may need to do a bit looking around :

-----------------------------
> modprobe pcnet32
> ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:10:83:34:BA:E5  
[...]
-----------------------------

	The configuration of 'ifrename' is simple, you just specify
which name should be used for each MAC address in the file
/etc/iftab :

--------- /etc/iftab ------------------------
# HP 100VG J2585B PCI card
eth2		mac 08:00:09:*

# Old AT&T Wavelan ISA card
eth3		mac 08:00:0E:*

# AMD AMD PCnet LANCE PCI card
eth4		mac 00:10:83:*
---------------------------------------------

	The '*' in the MAC address is a wildcard and allow me to
replicate my configuration between multiple identical computers. If
you have to manage large number of computers (like a rack of server or
clusters), you may want to look at other selectors offered by
'ifrename', such as the ability to base interface name on Bus
Information.

	To test that ifrename works, do the following :
		o load all your drivers, see section (2)
		o check /proc/net/dev to see which interface exist
		o bring all interfaces down : ifconfig ethX down
		o run ifrename
		o check each interface with ifconfig

	6) Configuring interfaces
	-------------------------
	Most likely, your distribution is already doing this part
properly. Just assign the proper IP and wireless configuration to each
of the interface name you have chosen.
	This part is distribution specific, and I already document it
in the file DISTRIBUTIONS.txt.

	In Debian, you would need to modify the file
/etc/network/interfaces like this :

--------- /etc/network/interfaces -----------
# AMD AMD PCnet LANCE PCI card
auto eth4
iface eth4 inet dhcp

# HP 100VG J2585B PCI card
auto eth2
iface eth2 inet static
    address 10.0.0.2
    network 10.0.0.0
    netmask 255.255.255.0
    broadcast 10.0.0.255
    gateway 10.0.0.1
---------------------------------------------

	This was the last part. Now, at your next boot, all your
interfaces should be assigned the proper name and proper
configuration.

CONFIGURATION VIA HOTPLUG
-------------------------
	Dealing with removable interfaces is similar to built-in
interfaces, the only difference is that we will use the Hotplug
scripts instead of the init scripts. Another difference is that it
will require more work on your part because most distributions are not
fully ready for it.

	1) Applicability
	----------------
	The Hotplug configuration method is the best choice for any
removable network interface, such as :
		o Pcmcia (16 bits) network cards
		o CardBus (32 bits) network cards
		o USB network dongles
		o Hot-PCI network cards
	It may also be used to manage other types of network
interfaces, although it may not be the best choice for them.

	2) How Hotplug works
	--------------------
	Conceptually, Hotplug is very simple. When something
interesting happens, the Linux kernel generates an Hotplug event. This
run the proper script from the /etc/hotplug directory.
	There is 3 types of Hotplug events we care about :
		o PCI event : a CardBus device is added or removed
from the system. The script /etc/hotplug/pci.agent is run.
		o USB event : a USB device is added or removed
from the system. The script /etc/hotplug/usb.agent is run.
		o Network event : a network interface is added or
removed from the system. The script /etc/hotplug/net.agent is run.

	If we insert a CardBus network card in the system, the
following happens :
		1) Kernel detects new CardBus device
		2) Kernel generates PCI Hotplug event
		3) /etc/hotplug/pci.agent runs, find proper driver module
		4) /etc/hotplug/pci.agent loads driver module
		5) Driver module initialises, creates new network device
		6) Kernel detects new network device
		7) Kernel generates Network Hotplug event
		8) /etc/hotplug/net.agent runs, configure network device
	The sequence of events is similar for removals and USB devices.

	3) Make ifup reentrant
	----------------------
	<Most people should ignore this part>
	The first problem is that we need to make sure the command
'ifup' is fully reentrant. If the system has built-in interfaces, the
'ifup' may reenter itself at boot time :
		1) Init scripts start running
		2) Init script calls 'ifup -a' to initialise built-in network
			interfaces
		3) 'ifup' auto-loads driver module for built-in network
			interface 'eth4'
		4) Driver module initialises, creates new network device
		5) Kernel generates Network hotplug event
		6) /etc/hotplug/net.agent runs, call 'ifup eth4'
	You can produce the same reentrancy if want to manually load
module with the ifup command.

	The default version of 'ifup' for Debian 3.0 is not reentrant and
may deadlock during boot or if you use it manually. The patch to make
'ifup' properly reentrant is available here :
		http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=231197
	Later version of Debian (Sarge and later) have some workaround
that prevent deadlock in most case (but not fully eliminate them), so
for normal use the default 'ifup' should work fine.

	Other distributions have very different version of ifup, and I
have not tried those (tell me about it).

	4) Installing Hotplug for Debian Sarge (testing/unstable)
	---------------------------------------------------------
	Thanks to the great work of many people, Debian Sarge has all
the necessary packages and hotplug support, and will work mostly 'out
of the box'.
	You will need to install the following packages :
		o hotplug
		o ifrename

	While the installation of Hotplug is simple, its configuration
may seem complex. The current network Hotplug script has 3 modes,
'all', 'auto' and 'hotplug', however for our purpose they all produce
the same results when configured. This is controlled by the variable
NET_AGENT_POLICY in /etc/default/hotplug.

	In the mode "all", all interfaces are processed by
'ifup'. This will work without further configuration.

	In the mode "auto", only interfaces listed in a auto statement
in /etc/network/interfaces will be processed by 'ifup'. If you choose
this mode, you need to put in /etc/network/interfaces a statement auto
with the complete list of all interfaces.
--------- /etc/network/interfaces -----------
# Enable Hotplug support for "auto" mode (Sarge and later)
auto eth0 eth1 eth2 eth3 eth4 wlan0 wlan1 prism0 prism1 airo0 airo1
---------------------------------------------
	Unfortunately, this will make 'ifup' complain at boot time
that it can't find those interfaces. This is why I don't recommend
this mode.

	In the mode "hotplug", hotplug network events are ignored by
ifup by default. To enable them, therefore making this mode equal to
"all", you will need to add the following lines to
/etc/network/interfaces :
--------- /etc/network/interfaces -----------
# Enable Hotplug support for "hotplug" mode (Sarge and later)
mapping hotplug
    script echo
---------------------------------------------

	5) Installing Hotplug for Debian 3.0
	------------------------------------
	Debian 3.0 doesn't come by default with hotplug, but the
hotplug package is available as regular Debian package (on the CD or
downloadable via apt-get), so you can just install that.

	Unfortunately, this version of hotplug is not fully compatible
with kernel 2.6.X. You will need to do the following modifications to
the file /etc/hotplug/net.agent.

------- /etc/hotplug/net.agent ------------------
--- net.agent-d1        Fri Feb 20 18:18:05 2004
+++ net.agent   Fri Feb 20 18:22:50 2004
@@ -26,7 +26,7 @@ if [ "$INTERFACE" = "" ]; then
 fi
 
 case $ACTION in
-register)
+add|register)
 
     case $INTERFACE in
        # interfaces that are registered after being "up" (?)
@@ -52,7 +52,7 @@ register)
     mesg $1 $ACTION event not handled
     ;;
 
-unregister)
+remove|unregister)
     # Assume that we want to run ifdown no matter what,  
     # because it is not going to remove the data from the 
     # ifstate database otherwise.
-------------------------------------------------

	Compared to the version in Sarge, this older version of
hotplug is much more basic, and doesn't have any scanning at boot time
and doesn't need to be enabled in /etc/network/interfaces.

	6) Installing hotplug, other cases
	----------------------------------
	The canonical version of hotplug is available at :
		http://linux-hotplug.sourceforge.net/

	Most distributions have various version of hotplug with
various modifications on top of the canonical version, and chances are
that the canonical version won't completely work on your system.
	All these various changing versions make it difficult for me
to tell what exactly need to be changed in the hotplug scripts to make
them work.

	Some version of hotplug will do scan at boot time, see section
(4) for my comments on this.

	My guess is that in a few release, all these problems will
sort themselves out. Just be patient.

	7) Dealing with 'init' hotplug
	------------------------------
	In addition to the standard kernel Hotplug events, modern
versions of the Hotplug scripts add init scripts that scan the system
buses and generate pseudo Hotplug events. For the PCI buses, the
script /etc/hotplug/pci.rc is run after the boot, for the USB bus,
/etc/hotplug/usb.rc is run.
	The end result is that the Hotplug subsystem will also attempt
to configure built-in devices :
		1) Kernel boots
		2) Init runs, start to initialise the OS
		3) /etc/hotplug/pci.rc runs, generate pseudo Hotplug event
		4) /etc/hotplug/pci.agent loads driver module
		5) Driver module initialises, creates new network device
		6) Kernel generates Network Hotplug event
		7) /etc/hotplug/net.agent runs, configure network device

	At this point, you realise that at initialisation, both
Hotplug and the regular init scripts (see "CONFIGURATION FROM INIT
SCRIPTS") are trying to configure the same devices in parallel. This
may create problem, and it is totally redundant.
	Another reason I don't like this mechanism is that it blindly
attempt to load drivers for all hardware present on the system, and
don't use the configuration in /etc/modules.conf to select the proper
driver. It's fairly common to have multiple driver for some hardware,
and because of Murphy's law, Hotplug will usually load the wrong
one. It's also fairly common to have hardware on the system that
doesn't need enabling (for example, the IDE controller on my SCSI
machine), not loading the driver makes your kernel smaller and boot
faster.
	Unfortunately, Hotplug did not provide a simple way to disable
such a feature. More importantly, there is no way to selectively
disable it (let say, disabled for network, enabled for sound).

	One way to disable this functionality is to delete or rename
the files /etc/hotplug/pci.rc and /etc/hotplug/usb.rc.

	8) Making hotplug scripts call ifrename
	---------------------------------------
	The last hotplug step is to make sure that 'ifrename' is run
by the hotplug subsystem at the right time. As before, we want to run
it just before calling 'ifup'.
	The latest version of the hotplug scripts have this
integrated. However, you need to check that the path they use for
calling 'ifrename' is the proper one on your system. And, for older
versions of hotplug scripts, you will need to add this support
yourself.

	Check the path for ifrename :
--------------------------
> which ifrename
/sbin/ifrename
--------------------------

	The patch to add 'ifrename' to hotplug looks like :

------- /etc/hotplug/net.agent ------------------
--- net.agent-s2        Fri Feb 20 17:18:46 2004
+++ net.agent   Fri Feb 20 17:32:43 2004
@@ -40,6 +40,21 @@ add|register)
            # we can't do much here without distro-specific knowledge
            # such as whether/how to invoke DHCP, set up bridging, etc.
 
+           # Run ifrename as needed - Jean II
+           # Remap interface names based on MAC address. This workaround
+           # the dreaded configuration problem "all my cards are 'eth0'"...
+           # This needs to be done before ifup otherwise ifup will get
+           # confused by the name changed and because iface need to be
+           # down to change its name.
+           if [ -x /sbin/ifrename ] && [ -r /etc/iftab ]; then
+               debug_mesg invoke ifrename for $INTERFACE
+               NEWNAME=`/sbin/ifrename -i $INTERFACE`
+               if [ -n "$NEWNAME" ]; then
+                   debug_mesg iface $INTERFACE is remapped to $NEWNAME
+                   INTERFACE=$NEWNAME
+               fi;
+           fi
+
            # RedHat and similar
            export IN_HOTPLUG=1
            if [ -x /sbin/ifup ]; then
-------------------------------------------------

	If your hotplug scrips already include ifrename support, you
should find a section in /etc/hotplug/net.agent looking like the patch
above. Otherwise, just cut'n'paste the patch above in the right place.
	The path for 'ifrename' is used twice above, so don't forget
to modify both occurences...


	9) Loading driver modules
	-------------------------
	Wow ! The most difficult part is done.
	In theory, you don't need to do any specific configuration for
the driver modules to be loaded. The 'pci.agent' and 'usb.agent'
should load the right driver module for you.
	Also, you don't need to define aliases in /etc/modprobe.conf,
it's useless (and may be counter productive).

	If you use driver compiled statically in the kernel, you also
have nothing to do.

	10) Renaming interfaces
	-----------------------
	We still use ifrename to assign names to interfaces. The
configuration of 'ifrename' is the same. To keep the possibility of
having multiple wireless cards (one in each CardBus slot), we use
wildcards in both the MAC address and the name :

--------- /etc/iftab -----------------------
# SMC 2835W wireless CardBus card
prism*		mac 00:30:B4:*
---------------------------------------------

	If you insert two cards, they would be named prism0 and
prism1. Note that 'name wildcarding' is a feature only available in
2.6.X, so if you use 2.4.X you will need to be explicit and list each
card separatly :

--------- /etc/iftab -----------------------
# SMC 2835W wireless CardBus card
prism0		mac 00:30:B4:64:27:8B
prism1		mac 00:30:B4:64:27:8D
---------------------------------------------

	11) Configuring interfaces
	-------------------------
	At this point, configuration of Hotplug interfaces is done
just like their built-in counterparts. This part is still distribution
specific, and still already document in the file DISTRIBUTIONS.txt..

	In Debian, you would need to modify the file
/etc/network/interfaces like this :

--------- /etc/network/interfaces -----------
# Enable Hotplug support (Sarge and later)
mapping hotplug
    script echo

# SMC 2835W wireless CardBus card
iface prism0 inet static
    address 10.0.1.2
    network 10.0.1.0
    netmask 255.255.255.0
    broadcast 10.0.1.255
    wireless-essid THE_ESSID
    wireless-mode ad-hoc
    wireless-channel 5
---------------------------------------------

	Now, just cross your finger and plug the card in the slot...

PCMCIA INTERFACES (16 bits)
---------------------------
	The Pcmcia subsystem has quite some legacy, and can use
various configuration procedure. The Pcmcia subsystem fully use
hotplug for 32 bits card (if you are using the kernel Pcmcia modules,
which is the only option for 2.6.X). For 16 bits cards, we can't make
them fully hotplug yet and need the cardmgr and /etc/pcmcia directory,
however we can make their network configuration use hotplug.

	To use Hotplug network configuration with 16 bits Pcmcia
cards, first make sure the Pcmcia subsystem is properly configured and
that cardmgr load the right module (in most case, it should). Then,
make sure that you don't have any configuration entries in
/etc/pcmcia/network.opts and /etc/pcmcia/wireless.opts. Make sure that
none of entries in your system network configuration use 'eth0' or
'wlan0' (in /etc/network/interfaces for Debian users).
	Then, just follow the procedure described above for
"Configuration Using Hotplug" to configure your network cards.

	You might want a little bit of explanation on why this magic
will work (which would help in case it doesn't work).
	There is two types of Pcmcia network configuration scripts,
available as /etc/pcmcia/network. The original Pcmcia script configure
network cards using options found in /etc/pcmcia/network.opts and
/etc/pcmcia/wireless.opts. Most distributions replace it with a script
calling 'ifup'. By making sure that network.opts and wireless.opts are
"empty", we neutralise the first set of scripts. By making sure no
system configuration uses 'eth0' or 'wlan0', we neutralise the second
set of scripts, the script would call 'ifup' with the default
interface name, which is usually 'eth0', ifup would not find a
configuration for it and would just ignores it.
	The card would still be configured because hotplug network
events are generated for every interfaces, not only for devices
managed by hotplug. So, net.agent would receive an event and perform
the necessary steps to configure it.

	Personally, I'm still using the original Pcmcia scripts for my
Pcmcia cards as described in the file PCMCIA.txt, because I will
migrate my complex configurations over time.
	You can also decide to not use Hotplug for Pcmcia cards and
modify the distribution Pcmcia scripts in /etc/pcmcia/* to handle
Pcmcia cards properly. You would need to modify /etc/pcmcia/network to
add 'ifrename' before 'ifup' the same way it was done for
/etc/hotplug/net.agent. But, as in the long term Pcmcia will migrate
to Hotplug, I would not bother...

MANUAL LOADING, DOCKING STATIONS
--------------------------------
	Manual loading is used for built-in network interfaces that
are only use at specific time, and that you want disabled the rest of
the time. We assume that you still use modules so that when the
interface is not used you can remove the driver from the kernel.

	First, you need to set the configuration for those interfaces,
the same way it's done for other network interfaces. The main
difference is that you need to specify that those interfaces should
not be enabled at boot time. It's also a good idea to disable Hotplug
init scripts.
	With Debian, you just need to make sure that the 'auto"
keyword doesn't apply to this interface.
--------- /etc/network/interfaces -----------
# AMD AMD PCnet LANCE PCI card
iface eth4 inet dhcp
---------------------------------------------

	If you use driver statically built in the kernel, you can just
enable and disable those interfaces with 'ifup ethX' and 'ifdown ethX'.

	If you use both a modular system and 'ifrename', you will need
to change your habits when enabling those devices. The classical 'ifup
ethX' won't work.
	If you don't use Hotplug, you need to do :
-----------------------------------
modprobe eth4
ifrename
ifup eth4
-----------------------------------
	If you use hotplug, you only need to do :
-----------------------------------
modprobe eth4
-----------------------------------

	On the other hand, disabling the interface has not changed :
-----------------------------------
ifdown eth4
modprobe -r eth4
-----------------------------------
	Using "modprobe -r" make sure that if the driver is composed
of multiple module all the modules are unloaded.

	Docking stations for laptops may contain built-in
interfaces. My previous laptop had one, and Linux had no support for
it. To be able to simply manage my docking station, I had created two
little scripts to enable and disable my network interface.
	After docking, you would run :
-------- /sbin/dock ----------------------------
#!/bin/sh
modprobe eth4
ifrename
ifup eth4
------------------------------------------------
	And prior to undocking, you would run :
-------- /sbin/undock ----------------------------
#!/bin/sh
ifdown eth4
modprobe -r eth4
------------------------------------------------
	Thanks to 'ifrename', the network interface in your dock will
always be properly configured regardless of if you have a Pcmcia
network card in the Pcmcia slot or not.

SCHEMES (MULTI-CONFIG)
----------------------
	Most Ethernet cards will only connect to a single network, or
can use DHCP to be auto-configured. With Wireless Cards, it's much
more likely that you will need multiple configurations, for example at
work, at home and on-the-go.

	Most distributions have various level of support for such
schemes. Some distributions offer simple network schemes, while other
offer "overall" schemes changing the whole configuration. I document
the support for schemes in various distributions in the file
DISTRIBUTIONS.txt.

	You can also use tools such as IfPlugd, WapRoamd or
Wlandetect. Those tools are a kind of "wireless-DHCP", they attempt to
automatically detect the proper wireless configuration and apply
it. Most will also attempt to detect network changes.
	The main limitation of those tools is that they offer very
little manual control. If two valid alternatives are possible, you
can't switch between them. If a configuration can't be detected, they
usually fail.
	That's the same concept as using DHCP versus Static IP
addresses. Some people are very happy with DHCP, my style is Static IP
addresses.

	If you use Debian and want to use simple manual schemes, these
are the things you need to do.
	1) Make sure that 'ifscheme' and 'ifscheme-mapping' are
installed on the system. You may find them in a separate tar file on
my web site.
	2) Check the path for 'ifscheme-mapping' (using whereis).
	3) Modify you /etc/network/interface to add proper mapping and
configuration.

------- /etc/network/interfaces ----------------------
# Enable Hotplug support (Sarge and later)
mapping hotplug
    script echo

# SMC 2835W wireless CardBus card
mapping prism0
    script /sbin/ifscheme-mapping

iface prism0-any inet dhcp
    wireless-essid any
    wireless-mode managed

iface prism0-adhoc inet static
    address 10.0.1.2
    network 10.0.1.0
    netmask 255.255.255.0
    broadcast 10.0.1.255
    wireless-essid THE_ESSID
    wireless-mode ad-hoc
    wireless-channel 5

iface prism0-other inet static
    address 10.10.10.2
    network 10.10.10.0
    netmask 255.255.255.0
    broadcast 10.10.10.255
    wireless-essid ANOTHER_ESSID
    wireless-mode ad-hoc
    wireless-key "s:secure"
------------------------------------------------------

FIRMWARE LOADING
----------------
	A lot of modern wireless card don't have built in firmware and
need firmware loading. Recent kernel (2.6.X) have a firmware
loader. These are a few notes on how to use it.

	First, read the documentation coming with your driver, because
each driver has specificities (like the name of the firmware file it
requires).

	You need to compile your kernel with firmware loading
(CONFIG_FW_LOADER in "Generic Driver Options"). If your driver was
built from the kernel, chances are that it enabled this feature
already. Make sure you boot from this new kernel.

	The 'sysfs' file system must be mounted. The easiest is to
mount it at boot time, add a line for it in /etc/fstab :

-------- /etc/fstab ------------------------------
sysfs		/sys	      sysfs  defaults                   0      0
--------------------------------------------------

	Then, you add the firmware file in the directory where it's
expected, which is /usr/lib/hotplug/firmware/ in most cases.

	Most distributions nowadays have a version of the Hotplug
scripts that knows how to deal with firmware. If it is not the case,
just grab the 'firmware.agent' file from an alternate source and copy
it into your /etc/hotplug directory (make sure it's executable).
	You can try the canonical version :
		http://linux-hotplug.sourceforge.net/
	Or Debian's version :
		http://packages.debian.org/unstable/admin/hotplug

	Note that firmware loading will usually only work with
interfaces that are fully managed by Hotplug. This is the only way to
ensure the that proper sequence of action is happening in the right
order every time. Firmware loading will usually not work properly for
interfaces configured in the init scripts.
	This means that if you have a built-in interface that require
firmware loading, you should just use manage those interfaces like
removable interfaces (see section above). However, interface
configuration need to be explicitely triggered at boot time.

	One possibility is to set-up Hotplug to be run from the init
script at boot time. This is usually an option for recent
distributions (it's not the case for Hotplug in Debian 3.0). But, we
have seen that this has some issues.
	The other possibility is to use an hybrid between the init
script method and the hotplug method. First, you need to add an alias
for the driver in /etc/modprobe.conf. Then, you need to specify a
mapping for this interface in /etc/iftab, and specify a configuration
for this interface and that that it is enabled at boot time. Lastly,
you make sure that the network init scripts run 'ifrename
-p'. 'Ifrename' will trigger the module to load, and all the Hotplug
events will be generated properly to configure the interface.

DEVICES WITH MULTIPLE NAMES
---------------------------
	Some wireless drivers offer multiple network interfaces for
the same device. A classical example is the Aironet driver that
creates a 'ethX' and 'wifiY' for each card.

	'ifrename' allow you a finer selection of interfaces than
'nameif'. For example, to only rename the pseudo-Ethernet network
interface name of the Aironet driver, you would do :

--------- /etc/iftab -----------------------
# Cisco Aironet 350 wireless Pcmcia card
airo*		mac 00:07:0E:* arp 1
---------------------------------------------

	After that, your device would be available through 'eth0' and
'wifi0'.

	You can rename both interfaces. You just need to remember that
'ifrename' start matching from the last line of the file, so you would
do :
--------- /etc/iftab -----------------------
# Cisco Aironet 350 wireless Pcmcia card
wifi*		mac 00:07:0E:*
airo*		mac 00:07:0E:* arp 1
---------------------------------------------

	The current version of 'ifrename' support only the most useful
selectors, and is architectured such as adding selectors is relatively
trivial. If you find a case that 'ifrename' can't handle, you should
just extend it.

DEVICES WITHOUT MAC ADDRESSES
-----------------------------
	Most Ethernet and Wireless devices have a fixed and unique MAC
address, and it is therefore advised to name them based on this
criteria. However, there is also network interfaces that don't have a
fixed and unique MAC address, for example Ethernet over USB, IP over
FireWire, PPP and tunnel interfaces.
	The driver for those devices create the interface with a name
specific to the driver, such as ppp* for PPP interfaces and usb* for
Ethernet over USB, and therefore they are easy to identify and
configure, and few users feel the need to rename them. Moreover, some
of them, such as PPP, have their own configuration scripts and
methodology addressing their unique needs.

	There is a few cases where you might want to rename interfaces
withour MAC addresses. One example is two Ethernet over USB
dongles. The way to do this is to use alternate ifrename
selectors. Choosing the right selector depend on what you want to
achieve.
	A quick theoretical example to illustrate :
--------- /etc/iftab -----------------------
# All other usbnet devices
usb*		driver usbnet
# Specific usbnet devices
usb-p		firmware "Prolific PL-2301/PL-2302"
usb-4		bus-info usb-00:02.0-1.4
---------------------------------------------

TROUBLESHOOTING
---------------
	If your interface doesn't show up as expected with ifconfig,
you will need to find out why. First, you need to be familiar with the
sequence of actions in the system and find which one did not happen.

	You need to check if the driver module(s) was loaded using
'lsmod'.

	You need to check if the interface was properly renamed with
'ifrename'. You can use 'ifrename -D -V' to debug your /etc/iftab.
	Get the the list of interfaces on your system with 'cat
/proc/net/dev', and check if an interface is using the name you
assigned or 'eth0'. Check any suspicious interfaces with 'ifconfig
eth0', and check its MAC address. Note that some rare drivers don't
have a proper MAC address before brought up, which fools ifrename.
	Verify that no line in /etc/iftab matches the all-zero MAC
address. The all-zero MAC address matches the loopback interface 'lo'
and various pseudo network devices, renaming the loopback interface is
highly discouraged.

	You need to check which configuration was given to the
interface using 'ifconfig' and 'iwconfig'.

	The Hotplug subsystem has also good debugging facilities.
	To enable Hotplug debugging, just make sure the variable DEBUG
is defined in /sbin/hotplug :
--------- /sbin/hotplug ------------------------------
--- /sbin/hotplug-old      Tue Mar 26 09:00:20 2002
+++ /sbin/hotplug       Fri Feb 20 18:40:38 2004
@@ -22,7 +22,7 @@
 cd /etc/hotplug
 . hotplug.functions
 
-# DEBUG=yes export DEBUG
+DEBUG=yes export DEBUG
 
 if [ "$DEBUG" != "" ]; then
     mesg "arguments ($*) env (`env`)"
------------------------------------------------------
	Then, you can check your message logs for Hotplug events with
'tail -f /var/log/messages'. Verify that the various Hotplug events
happen as expected (pci, firmware, net...), and verify the log
messages from 'net.agent'.


	Have fun...

	Jean
