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