This howto will show you how to combine 2 NICs into 1, commonly referred to as NIC bonding.

Applicable to Centos Versions:

  • Centos 5.x
  • Centos 6.x

Requirements

Explanation of requirements.

  1. Root access to the system
  2. 2 physical network cards

Doing the work

Basic description of what will be done and what is expected.

  1. Create bond0 config file:
    2. vi /etc/sysconfig/network-scripts/ifcfg-bond0
  2. Add the following lines:
    3. 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, esc :wq)
  3. Edit eth0 config file:
    4. vi /etc/sysconfig/network-scripts/ifcfg-eth0
  4. Add the following lines:
    5. DEVICE=eth0
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=none
  5. Edit eth1 config file:
    6. vi /etc/sysconfig/network-scripts/ifcfg-eth1
  6. Add the following lines:
    7. DEVICE=eth1
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=none
  7. Load the modules on boot:
    8. vi /etc/modprobe.conf
  8. Add the following lines: 
    9. alias bond0 bonding
options bond0 mode=balance-alb miimon=100

Troubleshooting

How to test

Explanation troubleshooting basics and expectations.

  1. Load the modules, restart the network show the satus of the interface:
    2. modprobe bonding && service network restart && less /proc/net/bonding/bond0
  2. Output:
    3. Bonding Mode: load balancing (round-robin)MII Status: upMII Polling Interval (ms): 0Up Delay (ms): 0Down Delay (ms): 0

Slave Interface: eth0MII Status: upLink Failure Count: 0Permanent HW addr: 00:0c:29:c6:be:59

Slave Interface: eth1MII Status: upLink Failure Count: 0Permanent HW addr: 00:0c:29:c6:be:63
  3. list the interfaces seen by the system:
    4. ifconfig
  4. Output:
    5. 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

Common problems and fixes

Common problems described here, include links to known common problems if located on another site.

More Information

Any additional information or notes.

Disclaimer

We test this stuff on our own machines, really we do. But you may run into problems, if you do, come to #centoshelp on irc.freenode.net

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