Linux bond or team multiple network interfaces (NIC) into single interface

Linux allows binding multiple network interfaces into a single channel/NIC using special kernel module called bonding. According to official bonding documentation, "The Linux bonding driver provides a method for aggregating multiple network interfaces into a single logical "bonded" interface. The behavior of the bonded interfaces depends upon the mode; generally speaking, modes provide either hot standby or load balancing services. Additionally, link integrity monitoring may be performed."

Step #1: Create a bond0 configuration file

Red Hat Linux stores network configuration in /etc/sysconfig/network-scripts/ directory. First, you need to create bond0 config file:
# vi /etc/sysconfig/network-scripts/ifcfg-bond0

Append following lines to it:

DEVICE=bond0
IPADDR=192.168.1.20
NETWORK=192.168.1.0
NETMASK=255.255.255.0
USERCTL=no
BOOTPROTO=none
ONBOOT=yes

Replace above IP address with your actual IP address. Save file and exit to shell prompt.

Step #2: Modify eth0 and eth1 config files:

Open both configuration using vi text editor and make sure file read as follows for eth0 interface

# vi /etc/sysconfig/network-scripts/ifcfg-eth0

Modify/append directive as follows:

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

Open eth1 configuration file using vi text editor:# vi /etc/sysconfig/network-scripts/ifcfg-eth1

Make sure file read as follows for eth1 interface:

DEVICE=eth1
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=none

Save file and exit to shell prompt.

Step # 3: Load bond driver/module

Make sure bonding module is loaded when the channel-bonding interface (bond0) is brought up. You need to modify kernel modules configuration file:

# vi /etc/modprobe.conf

Append following two lines:

alias bond0 bonding
options bond0 mode=balance-alb miimon=100

Save file and exit to shell prompt. You can learn more about all bounding options in kernel source documentation file (click here to read file online).

Step # 4: Test configuration

First, load the bonding module:

# modprobe bonding

Restart networking service in order to bring up bond0 interface:

# service network restart

Verify everything is working:

# less /proc/net/bonding/bond0

Output:

Bonding Mode: load balancing (round-robin)

MII Status: up

MII Polling Interval (ms): 0

Up Delay (ms): 0

Down Delay (ms): 0

Slave Interface: eth0

MII Status: up

Link Failure Count: 0

Permanent HW addr: 00:0c:29:c6:be:59

Slave Interface: eth1

MII Status: up

Link Failure Count: 0

Permanent HW addr: 00:0c:29:c6:be:63

List all interfaces:# ifconfig

Output:

bond0     Link encap:Ethernet  HWaddr 00:0C:29:C6:BE:59

 inet addr:192.168.1.20  Bcast:192.168.1.255  Mask:255.255.255.0

 inet6 addr: fe80::200:ff:fe00:0/64 Scope:Link

 UP BROADCAST RUNNING MASTER MULTICAST  MTU:1500  Metric:1

 RX packets:2804 errors:0 dropped:0 overruns:0 frame:0

 TX packets:1879 errors:0 dropped:0 overruns:0 carrier:0

 collisions:0 txqueuelen:0

 RX bytes:250825 (244.9 KiB)  TX bytes:244683 (238.9 KiB)

eth0      Link encap:Ethernet  HWaddr 00:0C:29:C6:BE:59

 inet addr:192.168.1.20  Bcast:192.168.1.255  Mask:255.255.255.0

 inet6 addr: fe80::20c:29ff:fec6:be59/64 Scope:Link

 UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1

 RX packets:2809 errors:0 dropped:0 overruns:0 frame:0

 TX packets:1390 errors:0 dropped:0 overruns:0 carrier:0

 collisions:0 txqueuelen:1000

 RX bytes:251161 (245.2 KiB)  TX bytes:180289 (176.0 KiB)

 Interrupt:11 Base address:0x1400

eth1      Link encap:Ethernet  HWaddr 00:0C:29:C6:BE:59

 inet addr:192.168.1.20  Bcast:192.168.1.255  Mask:255.255.255.0

 inet6 addr: fe80::20c:29ff:fec6:be59/64 Scope:Link

 UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1

 RX packets:4 errors:0 dropped:0 overruns:0 frame:0

 TX packets:502 errors:0 dropped:0 overruns:0 carrier:0

 collisions:0 txqueuelen:1000

 RX bytes:258 (258.0 b)  TX bytes:66516 (64.9 KiB)

 Interrupt:10 Base address:0x1480