Using Bonded Ethernet Network Interfaces

For a set-up where there is a high-throughput of information being written, consider using bonded network interfaces. This is where you combine the connectivity of more than one network port, increasing the throughput linearly according to the number of bonded connections.

Bonding also provides an additional benefit in that with multiple network interfaces effectively supporting the same communications channel, a fault within a single network interface in a bonded group does not stop communication. For example, imagine you have a bonded setup with four network interfaces providing a single interface channel between two DRBD servers. If one network interface fails, communication can continue on the other three without interruption, although at a lower speed.

To enable bonded connections you must enable bonding within the kernel. Then configure the module to specify the bonded devices and then configure each new bonded device just as you would a standard network device:

To configure the bonded devices, edit the /etc/modprobe.conf file (Red Hat) or add a file to the /etc/modprobe.d directory. In each case, you define the parameters for the kernel module. First, specify each bonding device:
```
alias bond0 bonding
```
You can then configure additional parameters for the kernel module. Typical parameters are the mode option and the miimon option.
The mode option specifies how the network interfaces are used. The default setting is 0, which means that each network interface is used in a round-robin fashion (this supports aggregation and fault tolerance). Using setting 1 sets the bonding mode to active-backup. This means that only one network interface is used as a time, but that the link automatically fails over to a new interface if the primary interface fails. This settings only supports fault-tolerance.
The miimon option enables the MII link monitoring. A positive value greater than zero indicates the monitoring frequency in milliseconds for checking each slave network interface that is configured as part of the bonded interface. A typical value is 100.
You set th options within the module parameter file, and you must set the options for each bonded device individually:
```
options bond0 miimon=100 mode=1
```
Reboot your server to enable the bonded devices.
Configure the network device parameters. This is a two-part process: set up the bonded device configuration, then configure the original network interfaces as 'slaves' of the new bonded interface.
- For Red Hat Linux:
  Edit the configuration file for the bonded device. For device bond0, this would be /etc/sysconfig/network-scripts/ifcfg-bond0:
```
DEVICE=bond0
BOOTPROTO=none ONBOOT=yes GATEWAY=192.168.0.254
NETWORK=192.168.0.0
NETMASK=255.255.255.0
IPADDR=192.168.0.1
USERCTL=no
```
  Then for each network interface to be part of the bonded device, configure the interface as a slave to the 'master' bond. For example, the configuration of eth0 in /etc/sysconfig/network-scripts/ifcfg-eth0 might look like this::
```
DEVICE=eth0
BOOTPROTO=none HWADDR=00:11:22:33:44:55
ONBOOT=yes TYPE=Ethernet MASTER=bond0
SLAVE=yes
```
- For Debian Linux:
  Edit the /etc/iftab file and configure the logical name and MAC address for each devices. For example:
```
eth0 mac 00:11:22:33:44:55
```
  Now set the configuration of the devices in /etc/network/interfaces:
```
auto bond0
 iface bond0 inet static
 address 192.168.0.1
 netmask 255.255.255.0
 network 192.168.0.0
 gateway 192.168.0.254
 up /sbin/ifenslave bond0 eth0
 up /sbin/ifenslave bond0 eth1
```
- For Gentoo:
  Use emerge to add the net-misc/ifenslave package to your system.
  Edit the /etc/conf.d/net file and specify the network interface slaves in a bond, the dependencies and then the configuration for the bond itself. A sample configuration might look like this:
```
slaves_bond0='eth0 eth1 eth2'
config_bond0=( '192.168.0.1 netmask 255.255.255.0' )
depend_bond0() {
need net.eth0 net.eth1 net.eth2
}
```
  Then make sure that you add the new network interface to list of interfaces configured during boot:
```
root-shell> rc-update add default net.bond0
```

Once the bonded devices are configured, reboot your systems.

You can monitor the status of a bonded connection using the /proc file system:

Using Bonded Ethernet Network Interfaces

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