HowTo do Ethernet Bonding on Ubuntu – Properly 8 Sep 08

It’s amazing how quickly guides on the Internet go out of date. I suppose this one will be no exception. However as I’ve been looking around there doesn’t appear to be a good guide as to how to get bonded ethernet to work in Ubuntu using the network helper scripts. So I thought I’d scribble down what I know.

This guide is designed for the Intrepid Ibex version of Ubuntu (8.10) with a small addendum covering Hardy Heron (8.04.1).

The Debian/Ubuntu networking system is a bit opaque. It works via a default script in /etc/network/interfaces and is described in interfaces(5). (run man interfaces to read it).

This gives you all the standard entries, but it also points out that other packages can install scripts that extend the options the interfaces file understands. And that is how you configure Ethernet bonding.

Configure your switch

Almost certainly you will have to activate LACP on the relevant ports on your switch to get automatic bonding to work. How you do this depends on your switch. (On my test HP 1800-8G switch I just use the web interface and check a couple of boxes).

For Intrepid and Hardy

1. Install the bonding enslave programs and network scripts:

   apt-get install ifenslave

2. Shutdown any active network interfaces you intend to use with bonding

   sudo -s
   ifdown eth0
   ifdown eth1
   etc, etc...

3. Comment out the ethernet configurations from /etc/network/interfaces

   #auto eth0
   #iface eth0 inet dhcp

4. Add in the bonding configuration into /etc/network/interfaces

   auto bond0
   iface bond0 inet dhcp
     slaves all
     bond-mode 4
     bond-miimon 100

5. Bring up the interface with:

   sudo ifup bond0

This brings up a bonded interface using the 802.3ad Link Aggregation Control Protocol (LACP) which is by far the easiest way of configuring a resilient trunk if your switch supports it (and even quite small switches do these days).

There are other modes and options available in the bonding driver all of which can now be specified in the interfaces file. Full gory details in the bonding.txt.gz file in the current linux-doc package.

Similarly you can specify which network interfaces you want to use as the slaves to the bonding driver e.g. slaves eth0 eth1. Look at the documentation in /usr/share/doc/ifenslave-2.6/README.Debian for more details.

Extra Work for Hardy

Hardy’s ifenslave scripts are a little more primitive than Intrepid. It doesn’t auto-load the bonding module the first time you try to use it and it doesn’t set the options automatically. You have to do that the old fashioned way.

1. Create a file called bonding in /etc/modprobe.d with the following config in it.

   alias bond0 bonding
   options bond0 mode=4 miimon=100

2. Load the module into the kernel

   sudo modprobe bond0

3. Clear out any failed bond interface by running ifdown

   sudo ifdown bond0

4. Bring the bond interface up.

   sudo ifup bond0

5. Once you done this once, the system will ensure that the module is loaded automatically on subsequent reboots and the network brought up.