NIC Bonding is a technique in which multiple Network Interface Cards (NICs) are logically bonded together and presented as a single interface to the outside world.

Before activating bonding it is recommended that the NICs are working alright. mii-tool can be used for this:

$ sudo /sbin/mii-tool
eth0: negotiated 100baseTx-FD, link ok
eth1: negotiated 100baseTx-FD, link ok

Bonding Driver in the Kernel

The first thing is to check whether the bonding driver module is already loaded or not.

$ sudo lsmod|grep bonding

If you do not see anything in the output then the bonding driver is not loaded. Most distribution’s default kernel compiles and installs the bonding driver module. To find out whether your distribution has the bonding driver module available. Use the following command:

$ sudo /sbin/modprobe --list | grep -i bonding
/lib/modules/2.6.8-2-386/kernel/drivers/net/bonding/bonding.ko

The output of the command shows that the bonding driver is available as a module. To load the bonding driver you can do the following:

$ sudo modprobe bonding
$ sudo lsmod|grep bonding
bonding                59112  0

If your distribution does not have the bonding driver module available then you need to recompile your kernel with the support. Select the “Bonding Driver Support” in the “Network Device Support” section. Remember to configure the driver as a module as currently it is the only way to pass parameters to it.
Configuring the bonding driver to load automatically at boot time.

To load the bonding driver automatically at boot time:

• On RHEL 3 modify the /etc/modules.conf file to contain the following:

  $ cat /etc/modules.conf
  alias bond0 bonding
  options bond0 miimon=100 mode=1 downdelay=2000 updelay=5000

• On RHEL 4 modify the /etc/modprobe.conf file to contain the following:

  $ cat /etc/modprobe.conf
  alias bond0 bonding
  options bond0 miimon=100 mode=1 downdelay=2000 updelay=5000

• On the Debian Sarge system with the 2.6.8 kernel, I had to create the /etc/modprobe.conf file and add the following lines to it.

  $ cat /etc/modprobe.conf
  alias bond0 bonding
  options bond0 miimon=100 mode=1 downdelay=2000 updelay=5000

  In debian if you install a package called modconf then there is another way to do this.

  $ sudo apt-get install modconf
  $ sudo /usr/sbin/modconf

modconf is ncurses based. Select the bonding driver modules from it and install it. Enter the parameters for the driver when prompted and exit from the utility. Your bonding driver is loaded with the parameters and also set to be loaded automatically next time the server reboots.

This method of using modconf basically modifies the /etc/modules file(which basically lists the modules to be loaded at boot time) to include the bonding driver name and creates a file by the driver name in /etc/modprobe.d/ to contain the parameters for the drivers. Here are the two files on my system:

$ cat /etc/modules
bonding
$ cat /etc/modprobe.d/bonding
options bonding mode=1 miimon=100 updelay=2000 downdelay=3000

Userspace Tools

You need the ifenslave utility also in addition to the bonding driver in the kernel. For Debian Sarge you can install the metapackage ifenslave. This currently points to the ifenslave-2.4 package. Since the Sarge has 2.4 kernel as the default if you just install ifenslave metapackage then ifenslave-2.4 will be installed. If you have installed the 2.6 kernel instead of the default 2.4 kernel then you should install ifenslave-2.6 package.

$ uname -a
Linux noddy 2.6.8-2-386 #1 Thu May 19 17:40:50 JST 2005 i686 GNU/Linux
$ sudo apt-get install ifenslave-2.6

Configuring the system

Once the bonding driver has been loaded with the required parameter, the system needs to be configured to use the bonding driver.

• Red Hat Enterprise Linux (all versions) and FedoraCreate a file /etc/sysconfig/network-scripts/ifcfg-bond0 with the following contents:

  DEVICE=bond0
  IPADDR=172.16.100.3
  NETMASK=255.255.0.0
  NETWORK=172.16.0.0
  BROADCAST=172.16.255.255
  ONBOOT=yes
  BOOTPROTO=none
  USERCTL=no
  PEERDNS=no
  TYPE=Ethernet
  GATEWAY=172.16.200.254

  Modify the file /etc/sysconfig/network-scripts/ifcfg-eth0 to contain the following:

  DEVICE=eth0
  USERCTL=no
  ONBOOT=yes
  MASTER=bond0
  SLAVE=yes
  BOOTPROTO=none
  TYPE=Ethernet

  For other NICs in the system which you want to bond together with eth0 do the same and replace eth0 with the respective NIC like eth1, eth2 and so on.

  Restart the networking:

  $ sudo /sbin/service network restart

• Debian and DerivativesOn Debian systems edit the /etc/network/interfaces file and remove the reference of all the NICs and just leave the loopback adapter details. Then add the following interface details:

  # The bonding interface
  auto bond0
  iface bond0
  inet static
  address 172.16.202.2
  netmask 255.255.0.0
  gateway 172.16.200.254
  
  up ifenslave bond0 eth0 eth1
  down ifenslave -d bond0 eth0 eth1

  After that a simple restart of networking services will bring the bonding interface up.

  $ sudo invoke-rc.d networking restart

ifconfig will list all the interfaces along with the bond0 interface. All will have the same MAC address and same ip address.