Linux Network bonding – setup guide

Linux network Bonding is a creation of a single bonded interface by combining 2 or more Ethernet interfaces. This helps in high availability of your network interface and offers performance improvements on your data traffic flow. Bonding is also referred as nic trunking or teaming.

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

Steps for bonding in Oracle Linux, CentOS and Redhat Enterprise Linux are as follows..

Step 1.

Create the file ifcfg-bond0 with the IP address, netmask and gateway. Shown below is my test bonding config file.

Step 2.

Modify eth0, eth1 and eth2 configuration as shown below. Comment out, or remove the ip address, netmask, gateway and hardware address from each one of these files, since settings should only come from the ifcfg-bond0 file above. Make sure you add the MASTER and SLAVE configuration in these files.

Step 3.

Set the parameters for bond0 bonding kernel module. Select the network bonding mode based on you need, documented at the bottom of this article. The modes are

  • mode=0 (Balance Round Robin)
  • mode=1 (Active backup)
  • mode=2 (Balance XOR)
  • mode=3 (Broadcast)
  • mode=4 (802.3ad)
  • mode=5 (Balance TLB)
  • mode=6 (Balance ALB)

Add the following lines to /etc/modprobe.conf .  Specifies the MII link monitoring frequency in milliseconds. This determines how often the link state of each slave is inspected for link failures.  A value of zero disables MII link monitoring.  A value of 100 is a good starting point.

Step 4.

Load the bond driver module from the command prompt.

Step 5.

Restart the network, or restart the computer.

When the machine boots up check the proc settings.

Look at ifconfig -a and check that your bond0 interface is active. You are done!.

To verify whether the failover bonding works..

  • Do an ifdown eth0 and check /proc/net/bonding/bond0 and check the “Current Active slave”.
  • Do a continuous ping to the bond0 ipaddress from a different machine and do a ifdown the active interface. The ping should not break.

Modes of bonding :

RHEL bonding supports 7 possible “modes” for bonded interfaces. These modes determine the way in which traffic sent out of the bonded interface is actually dispersed over the real interfaces. Modes 0, 1, and 2 are by far the most commonly used among them.
  • Mode 0 (balance-rr)
    This mode transmits packets in a sequential order from the first available slave through the last. If two real interfaces are slaves in the bond and two packets arrive destined out of the bonded interface the first will be transmitted on the first slave and the second frame will be transmitted on the second slave. The third packet will be sent on the first and so on. This provides load balancing and fault tolerance.
  • Mode 1 (active-backup)
    This mode places one of the interfaces into a backup state and will only make it active if the link is lost by the active interface. Only one slave in the bond is active at an instance of time. A different slave becomes active only when the active slave fails. This mode provides fault tolerance.
  • Mode 2 (balance-xor)
    Transmits based on XOR formula. (Source MAC address is XOR’d with destination MAC address) modula slave count. This selects the same slave for each destination MAC address and provides load balancing and fault tolerance.
  • Mode 3 (broadcast)
    This mode transmits everything on all slave interfaces. This mode is least used (only for specific purpose) and provides only fault tolerance.
  • Mode 4 (802.3ad)
    This mode is known as Dynamic Link Aggregation mode. It creates aggregation groups that share the same speed and duplex settings. This mode requires a switch that supports IEEE 802.3ad Dynamic link. Slave selection for outgoing traffic is done according to the transmit hash policy, which may be changed from the default simple XOR policy via the xmit_hash_policy option. Note that not all transmit policies may be 802.3ad compliant, particularly inregards to the packet mis-ordering requirements of section 43.2.4 of the 802.3ad standard. Differing peer implementations will have varying tolerances for noncompliance.
  • Mode 5 (balance-tlb)
    This is called as Adaptive transmit load balancing. The outgoing traffic is distributed according to the current load and queue on each slave interface. Incoming traffic is received by the current slave.
  • Mode 6 (balance-alb)
    This is Adaptive load balancing mode. This includes balance-tlb + receive load balancing (rlb) for IPV4 traffic. The receive load balancing is achieved by ARP negotiation. The bonding driver intercepts the ARP Replies sent by the server on their way out and overwrites the src hw address with the unique hw address of one of the slaves in the bond such that different clients use different hw addresses for the server.