11.2.4. Channel Bonding Interfaces

Red Hat Enterprise Linux allows administrators to bind multiple network interfaces together into a single channel using the bonding kernel module and a special network interface called a channel bonding interface. Channel bonding enables two or more network interfaces to act as one, simultaneously increasing the bandwidth and providing redundancy.

Warning

The use of direct cable connections without network switches is not supported for bonding. The failover mechanisms described here will not work as expected without the presence of network switches. See the Red Hat Knowledgebase article Why is bonding in not supported with direct connection using crossover cables? for more information.

Note

The active-backup, balance-tlb and balance-alb modes do not require any specific configuration of the switch. Other bonding modes require configuring the switch to aggregate the links. For example, a Cisco switch requires EtherChannel for Modes 0, 2, and 3, but for Mode 4 LACP and EtherChannel are required. See the documentation supplied with your switch and the bonding.txt file in the kernel-doc package (see Section 31.9, “Additional Resources”).

11.2.4.1. Check if Bonding Kernel Module is Installed

In Red Hat Enterprise Linux 6, the bonding module is not loaded by default. You can load the module by issuing the following command as root: 
~]# modprobe --first-time bonding
No visual output indicates the module was not running and has now been loaded. This activation will not persist across system restarts. See Section 31.7, “Persistent Module Loading” for an explanation of persistent module loading. Note that given a correct configuration file using the BONDING_OPTS directive, the bonding module will be loaded as required and therefore does not need to be loaded separately.
To display information about the module, issue the following command: 
~]$ modinfo bonding
See the modprobe(8) man page for more command options and see Chapter 31, Working with Kernel Modules for information on loading and unloading modules.

11.2.4.2. Create a Channel Bonding Interface

To create a channel bonding interface, create a file in the /etc/sysconfig/network-scripts/ directory called ifcfg-bondN, replacing N with the number for the interface, such as 0.
The contents of the file can be identical to whatever type of interface is getting bonded, such as an Ethernet interface. The only difference is that the DEVICE directive is bondN, replacing N with the number for the interface. The NM_CONTROLLED directive can be added to prevent NetworkManager from configuring this device.

Example 11.1. Example ifcfg-bond0 interface configuration file

The following is an example of a channel bonding interface configuration file: 
DEVICE=bond0
IPADDR=192.168.1.1
NETMASK=255.255.255.0
ONBOOT=yes
BOOTPROTO=none
USERCTL=no
NM_CONTROLLED=no
BONDING_OPTS="bonding parameters separated by spaces"
The MAC address of the bond will be taken from the first interface to be enslaved. It can also be specified using the HWADDR directive if required. If you want NetworkManager to control this interface, remove the NM_CONTROLLED=no directive, or set it to yes, and add TYPE=Bond and BONDING_MASTER=yes.
After the channel bonding interface is created, the network interfaces to be bound together must be configured by adding the MASTER and SLAVE directives to their configuration files. The configuration files for each of the channel-bonded interfaces can be nearly identical.

Example 11.2. Example ifcfg-ethX bonded interface configuration file

If two Ethernet interfaces are being channel bonded, both eth0 and eth1 can be as follows: 
DEVICE=ethX
BOOTPROTO=none
ONBOOT=yes
MASTER=bond0
SLAVE=yes
USERCTL=no
NM_CONTROLLED=no
In this example, replace X with the numerical value for the interface.
Once the interfaces have been configured, restart the network service to bring the bond up. As root, issue the following command: 
~]# service network restart
To view the status of a bond, view the /proc/ file by issuing a command in the following format: 
 cat /proc/net/bonding/bondN
For example: 
~]$ cat /proc/net/bonding/bond0
Ethernet Channel Bonding Driver: v3.6.0 (September 26, 2009)

Bonding Mode: load balancing (round-robin)
MII Status: down
MII Polling Interval (ms): 0
Up Delay (ms): 0
Down Delay (ms): 0
For further instructions and advice on configuring the bonding module and to view the list of bonding parameters, see Section 31.8.1, “Using Channel Bonding”.
Support for bonding was added to NetworkManager in Red Hat Enterprise Linux 6.3. See Section 11.2.1, “Ethernet Interfaces” for an explanation of NM_CONTROLLED and the NM_BOND_VLAN_ENABLED directive.

Important

In Red Hat Enterprise Linux 6, interface-specific parameters for the bonding kernel module must be specified as a space-separated list in the BONDING_OPTS="bonding parameters" directive in the ifcfg-bondN interface file. Do not specify options specific to a bond in /etc/modprobe.d/bonding.conf, or in the deprecated /etc/modprobe.conf file.
The max_bonds parameter is not interface specific and therefore, if required, should be specified in /etc/modprobe.d/bonding.conf as follows: 
options bonding max_bonds=1
However, the max_bonds parameter should not be set when using ifcfg-bondN files with the BONDING_OPTS directive as this directive will cause the network scripts to create the bond interfaces as required.
Note that any changes to /etc/modprobe.d/bonding.conf will not take effect until the module is next loaded. A running module must first be unloaded. See Chapter 31, Working with Kernel Modules for more information on loading and unloading modules.
11.2.4.2.1. Creating Multiple Bonds
In Red Hat Enterprise Linux 6, for each bond a channel bonding interface is created including the BONDING_OPTS directive. This configuration method is used so that multiple bonding devices can have different configurations. To create multiple channel bonding interfaces, proceed as follows:
  • Create multiple ifcfg-bondN files with the BONDING_OPTS directive; this directive will cause the network scripts to create the bond interfaces as required.
  • Create, or edit existing, interface configuration files to be bonded and include the SLAVE directive.
  • Assign the interfaces to be bonded, the slave interfaces, to the channel bonding interfaces by means of the MASTER directive.

Example 11.3. Example multiple ifcfg-bondN interface configuration files

The following is an example of a channel bonding interface configuration file: 
DEVICE=bondN
IPADDR=192.168.1.1
NETMASK=255.255.255.0
ONBOOT=yes
BOOTPROTO=none
USERCTL=no
NM_CONTROLLED=no
BONDING_OPTS="bonding parameters separated by spaces"
In this example, replace N with the number for the bond interface. For example, to create two bonds create two configuration files, ifcfg-bond0 and ifcfg-bond1.
Create the interfaces to be bonded as per Example 11.2, “Example ifcfg-ethX bonded interface configuration file” and assign them to the bond interfaces as required using the MASTER=bondN directive. For example, continuing on from the example above, if two interfaces per bond are required, then for two bonds create four interface configuration files and assign the first two using MASTER=bond0 and the next two using MASTER=bond1.