Network Card Bonding On CentOS

Bonding is the same as port trunking. In the following I will use the word bonding because practically we will bond interfaces as one. Bonding allows you to aggregate multiple ports into a single group, effectively combining the bandwidth into a single connection. Bonding also allows you to create multi-gigabit pipes to transport traffic through the highest traffic areas of your network. For example, you can aggregate three megabits ports into a three-megabits trunk port. That is equivalent with having one interface with three megabytes speed.

Where should I use bonding?

You can use it wherever you need redundant links, fault tolerance or load balancing networks. It is the best way to have a high availability network segment. A very useful way to use bonding is to use it in connection with 802.1q VLAN support (your network equipment must have 802.1q protocol implemented).

Diverse modes of bonding:

mode=1 (active-backup)
Active-backup policy: Only one slave in the bond is active. A different slave becomes active if, and only if, the active slave fails. The bond's MAC address is externally visible on only one port (network adapter) to avoid confusing the switch. This mode provides fault tolerance. The primary option affects the behavior of this mode.

mode=2 (balance-xor)
XOR policy: Transmit based on [(source MAC address XOR'd with destination MAC address) modulo slave count]. This selects the same slave for each destination MAC address. This mode provides load balancing and fault tolerance.

mode=3 (broadcast)
Broadcast policy: transmits everything on all slave interfaces. This mode provides fault tolerance.

mode=4 (802.3ad)
IEEE 802.3ad Dynamic link aggregation. Creates aggregation groups that share the same speed and duplex settings. Utilizes all slaves in the active aggregator according to the 802.3ad specification.

  • Prerequisites:
    • Ethtool support in the base drivers for retrieving the speed and duplex of each slave.
    • A switch that supports IEEE 802.3ad Dynamic link aggregation. Most switches will require some type of configuration to enable 802.3ad mode.

mode=5 (balance-tlb)
Adaptive transmit load balancing: channel bonding that does not require any special switch support. The outgoing traffic is distributed according to the current load (computed relative to the speed) on each slave. Incoming traffic is received by the current slave. If the receiving slave fails, another slave takes over the MAC address of the failed receiving slave.

  • Prerequisite: Ethtool support in the base drivers for retrieving the speed of each slave.

mode=6 (balance-alb)
Adaptive load balancing: includes balance-tlb plus receive load balancing (rlb) for IPV4 traffic, and does not require any special switch support. The receive load balancing is achieved by ARP negotiation. The bonding driver intercepts the ARP Replies sent by the local system on their way out and overwrites the source hardware address with the unique hardware address of one of the slaves in the bond such that different peers use different hardware addresses for the server.
Also you can use multiple bond interface but for that you must load the bonding module as many as you need.


In the /etc/modprobe.conf file add the following:

alias bond0 bonding
options bond0 miimon=80 mode=5

In the /etc/sysconfig/network-scripts/ directory create ifcfg-bond0:

IPADDR=<ip address>

Change the ifcfg-eth0 to:


Change the ifcfg-eth1 to:


That´s all! Now your trunk should be up and running!

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11 Comment(s)

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By: Anonymous

how do you remove a bonding?

tried going backwards, but I still see bond0 with the IP in ifconfig -a

By: Anonymous

I just removed/renamed the bonding config file in /etc/sysconfig/network-scripts after falling back to the original ifcfg-eth0/1/2/3 scripts (with no master/slave designation). 

By: RobM

"That´s all! Now your trunk should be up and running!"

Almost, you need to restart networking as well ("service network restart" or "/etc/init.d/network restart").

By: Vojtech

and also "modprobe bonding"

By: Anonymous


veeeeeeeery helpful...just did this on a CentOS 5.2 box with two onboard intel e1000s...

FYI for others, my nics were named eth2 and eth3, not 0&1. I was really scared to restart the network remotely, once I grew the balls to do so, it went offline for about a minute and I panicked, THANKFULLY it came back up and is now trunked...yaaay 8)

 another note: it started working without me running "modprobe bonding", but i ran it anyway.

By: musa


Would you please tell me which IPs you configured on eth2 and eth3 interfaces?... were they external or internal faces? and which IP did you configure on bond0 interface?

Actually i am stuck as to configure public IPs on my external interfaces)which i want to bind) of my centOS server or not? :(


By: Leonardo


 Is there a manner to do the same on Windows?

 Thanks in advance



on windows systems is called "NIC Temiang"...and actually is supported from all the vendors, You have to check if is available on your systems....

By: Chicago-man

Thanks! It worked great!!

By: Anonymous

Here is how to connect this with VLAN forwarding to KVM guest:

By: hophopper

I am trying to test the network redundancy on centos 6. When one particular slave interface is manually brought down, the putty session to the o.s goes down as well. When the other slave interface is brought down, the putty session to the o.s stays as it is. The o/p of "cat /proc/net/bonding/bond0" seems to be ok. I am trying this setup on Virtual-Box as of now. Am i doing something wrong ...Please help....(mode=1)