How to change the order of the network cards (eth1 <-> eth0) on linux

I am answering to my own question now because I finally found a workaround for this problem.

I found out that it is possible to reorder the devices by unloading the drivers and then loading them in correct order.

First method (bruteforce):

So the first method I came up with was simple to bruteforce the driver reload with init.d script.

Following init script is tailored for Debian 6.0, but the same principle should work on almost any distribution using proper init.d scripts.

#!/bin/sh -e

### BEGIN INIT INFO
# Provides:          reorder-nics
# Required-Start:
# Required-Stop:
# Default-Start:     S
# Default-Stop:
# Short-Description: Reloads the nics in correct order
### END INIT INFO

#
# This script should reload the nic drivers in corrected order.
# Basically it just unloads and then loads the drivers in different order.
#

echo "Reloading NICs!"

# unload the drivers
modprobe -r driver_0        # eth0 nic interface
modprobe -r driver_1        # eth1 nic interface

# load the drivers in corrected order
modprobe driver_1
modprobe driver_0

#EOF

Then the script must be added to proper runlevel directory. This can be done easily on Debian with "update-rc.d" command. For example: update-rc.d reorder-nics start S

Second method (Better I think):

I also found a bit more elegant way (at least for Debian & Ubuntu systems).

First Make sure that kernel doesn't automatically load the NIC drivers. This can be done by creating a blacklist file in /etc/modprobe.d/. I created a file named "disable-nics.conf". Note that files in /etc/modprobe.d/ must have .conf suffix. Also naming modules in /etc/modprobe.d/blacklist.conf do not affect autoloading of modules by the kernel, so you have to make your own file.

# Disable automatic loading of kernel driver modules
# Disable NIC drivers

blacklist driver_0     # eth0 by default
blacklist driver_1     # eth1 by default

Then run 'depmod -ae' as root

Recreate your initrd with 'update-initramfs -u'

And finally add the driver names in corrected order into /etc/modules file.

# /etc/modules: kernel modules to load at boot time.
#
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.
# Parameters can be specified after the module name.

# drivers in wanted order
driver_1    # this one should be loaded as eth0
driver_0    # this one should be loaded as eth1

Changes should come in effect after the next boot.

Reboot is not necessary though; it's easy to switch the devices with following command (as root, of course):

modprobe -r driver_0; modprobe -r driver_1; modprobe driver_1; modprobe driver_0

Some useful links I found while searching the solution:

  • http://www.macfreek.nl/mindmaster/Logical_Interface_Names
  • http://wiki.debian.org/KernelModuleBlacklisting
  • http://www.science.uva.nl/research/air/wiki/LogicalInterfaceNames

You can use the netdev= kernel command line parameter (you need to pass that to the kernel in grub) to instruct the kernel to link a given irq to a given interface, e.g.: netdev=irq=2,name=eth0

Tags:

Networking

Debian

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