Friday, October 20, 2006

Debian linux ethernet bonding

We're working on some fault tolerant delpoyments of debian linux systems. It turns out that this is available in the stock debian kernel (sarge) and luckily, in the custom kernel we'd built at a later time.

I dug up a few howto's out there, but none of them really had all of the pieces in one place, specifically for the packages that Debian uses out of the box.

Two software pieces are necessary - the "bonding" driver, and the "ifenslave" package. The bonding driver is in the default sarge kernel, and appears to be in the defaults during a kernel build. The "ifenslave" package is the userspace program used to control the binding of physical interfaces to the bonded driver. To install this, simply
apt-get install ifenslave-2.6
It's important to get the latest version; the version that installs with a plain "apt-get install ifenslave" doesn't seem to work properly.

Next, there are two files which need to change to tell the kernel to load the bonding driver. I appended these lines to the following files:


alias bond0 bonding
options bonding mode=active-backup miimon=100 max_bonds=1
If more than one bonding interface is needed, add additional aliases in this file, and increase the "max_bonds" option as necessary. We plan on using bonding on a few machines that act as routers, so they will need to have multiple bonded interface sets.

Finally, the bond0 interface must be set up in the /etc/network/interfaces file. More than likely there is an existing entry for your primary network interface, i.e. eth0. I just changed the interface name from eth0 to bond0, and added the following line:
up    ifenslave bond0 eth0 eth1
For reference, the entire /etc/network/interfaces file looks like this - notice that there are no individual entries for eth0 and eth1.
# generated by FAI
auto lo bond0
iface lo inet loopback
iface bond0 inet static
up ifenslave bond0 eth0 eth1
post-up /opt/tools/bin/init-ipmi
The linux Bonding howto is very comprehenive and covers the different modes of operation of this driver, as well as installation instructions for different flavors of linux and some discussion of deployment scenarios. We'll be expirimenting with various bonding modes this week to see what we can get away with; currently we're planning on running in the "active-backup" mode which is a simple active/passive failover.

Here are some other resources about linux/debian ethernet bonding:

More about bonding later!