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IFRENAME-VS-XXX.txt
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IFRENAME-VS-XXX.txt
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Network interface renaming comparison
-------------------------------------
INTRODUCTION
------------
The Wireless Tools package includes 'ifrename', a tool to
rename network interfaces. However, this is not the only solution to
the problem of renaming network interfaces. This document explain the
differences between ifrename and the various alternatives.
The subject of interface renaming may look simple at first
glance, and is simple in 95% of the cases, however there are many
complex scenario and those tools have many features, which explain why
we need to go in more details than just saying 'tool X is better'.
NAMEIF
------
The tool 'nameif' was designed to rename network
interfaces. It either loads mapping from the file /etc/mactab or
accept mapping on the command line.
It is part of the net-tools package :
http://www.tazenda.demon.co.uk/phil/net-tools/
Advantages over 'ifrename' :
+ More widespread, available in very old distributions
+ simpler/smaller
Drawbacks compared to 'ifrename' :
- Only support MAC address selector
- Does not support hotplug invocation
- Does not support module on-demand loading
Comments :
o The fact that nameif does not support selector other
than the MAC address is problematic, as USB-NET devices may not have
MAC addresses and some ethernet/wireless drivers can't query the MAC
address before 'ifconfig up'.
o 'ifrename' was designed as a better 'nameif', and
its concept is very similar.
IPROUTE
-------
The tool 'ip' can rename network interfaces with the following
syntax :
> ip link set <oldname> name <newname>
It is part of the 'iproute' package :
http://developer.osdl.org/dev/iproute2/
Advantages over 'ifrename' :
+ integrated in 'iproute', which most people need anyway
Drawbacks compared to 'ifrename' :
- Do not support any selector, must use old interface name
- No 'batch' mode, must rename each interface manually
Comments :
o 'ip' only provide the most basic facility. To use it
automatically, like in init/hotplug scripts, wrappers adding some
rules/selector must be written.
DRIVER MODULE PARAMETERS
------------------------
Some network driver have module parameters enabling to specify
the network name of all the devices created by the driver. This is
driver specific, so you will need to check your driver.
Advantages over 'ifrename' :
+ very simple to get configured and running
Drawbacks compared to 'ifrename' :
- Not universally supported : few drivers do it
- Fragmented : each driver does it differently
- The only selector available is the driver
Comments :
o This method was never popular with the kernel
people, and this feature is being removed from driver that use to
include it.
UDEV
----
The package 'udev' include facility to rename network
interfaces, with rules such as :
KERNEL="eth*", SYSFS{address}="00:52:8b:d5:04:48", NAME="lan"
This is part of the udev package :
http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev.html
Advantages over 'ifrename' :
+ simpler to setup if 'udev' is already properly setup
+ automatically generates persistent rules
Drawbacks compared to 'ifrename' :
- Less selectors that 'ifrename'
- Require kernel 2.6.X or later with sysfs support
- Do no support non-hotplug interfaces
- Require 'udev', not everybody uses it (static /dev, devfs)
Comments :
o 'udev' support many selectors, basically all those
present in 'sysfs' (excluding symlinks), even if the documentation
only show instructions to use the MAC address (which is problematic
with virtual devices some drivers - see above). 'ifrename' can also
use all selectors present in 'sysfs' (like 'udev'), can use sysfs
symlinks and parent directories, plus some other selectors not present
in sysfs that were found to be useful.
o Not all interfaces are managed by hotplug. All
virtual devices, such as tunnels and loopbacks, are not associated
with a hardware bus, and therefore are not managed by hotplug. All
driver compiled statically into the kernel are not managed by
hotplug. 'udev' can't deal with those devices.
o It is common practice on embedded system to use a
static /dev and not 'udev' to save space and boot time. And to not use
hotplug for the same reasons.
o 'ifrename' has now a udev compatiblity mode that
enables to trivially integrate it into 'udev' as an IMPORT rule. This
requires udev version 107 or better and ifrename 29-pre17 or better.
SELECTOR AWARE NETWORK SCRIPTS
------------------------------
Another method is to not rename the interface at all, and make
the various network script selector aware. The basic idea is to simply
ignore the interface name and have all the network scripts based on
selectors.
The main example is the original Pcmcia network scripts. They
allow you to configure an interface directly based on MAC address and
Pcmcia socket. Another example is the script get-mac-address.sh used
as a mapping in some Debian configuration. On the other hand, Red-Hat
and Fedora scripts don't apply, as they wrap around 'nameif'.
Advantages over 'ifrename' :
+ usually simpler to setup and understand
Drawbacks compared to 'ifrename' :
- Less selectors that 'ifrename'
- Only work for the scripts, other tools left confused
Comments :
o This method is conceptually simpler, and works
well. It eliminates the two steps process of other methods (renaming ;
configuring).
o Unfortunately, this method only apply to the
specific scripts, and not to the majority of the networking tools
which are still based on interface name. This means that when the user
use those other tools, he is left guessing which interface is which.
o Distributions never never really embraced this
method, as they all replaced the original Pcmcia scripts with one
using the interfacename.
Have fun...
Jean