Bonding modes under RHEL 5/6

Red Hat Enterprise Linux 5/6 supports the following bonding modes, the default policy is balance-rr.

 balance-rr or 0

 Round-robin policy: Transmit packets in sequential
 order from the first available slave through the
 last. This mode provides load balancing and fault
 tolerance.

 active-backup or 1

 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.

 In bonding version 2.6.2 or later, when a failover
 occurs in active-backup mode, bonding will issue one
 or more gratuitous ARPs on the newly active slave.
 One gratuitous ARP is issued for the bonding master
 interface and each VLAN interfaces configured above
 it, provided that the interface has at least one IP
 address configured. Gratuitous ARPs issued for VLAN
 interfaces are tagged with the appropriate VLAN id.

 This mode provides fault tolerance. The primary
 option, documented below, affects the behavior of this
 mode.

 balance-xor or 2

 XOR policy: Transmit based on the selected transmit
 hash policy. The default policy is a simple [(source
 MAC address XOR'd with destination MAC address XOR
 packet type ID) modulo slave count]. Alternate transmit
 policies may be selected via the xmit_hash_policy option,
 described below.

 This mode provides load balancing and fault tolerance.

 broadcast or 3

 Broadcast policy: transmits everything on all slave
 interfaces. This mode provides fault tolerance.

 802.3ad or 4

 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.

 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, documented below. Note that not all transmit
 policies may be 802.3ad compliant, particularly in
 regards 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.

 Prerequisites:

 1. Ethtool support in the base drivers for retrieving
 the speed and duplex of each slave.

 2. A switch that supports IEEE 802.3ad Dynamic link
 aggregation.

 Most switches will require some type of configuration
 to enable 802.3ad mode.

 balance-tlb or 5

 Adaptive transmit load balancing: channel bonding that
 does not require any special switch support.

 In tlb_dynamic_lb=1 mode; the outgoing traffic is
 distributed according to the current load (computed
 relative to the speed) on each slave.

 In tlb_dynamic_lb=0 mode; the load balancing based on
 current load is disabled and the load is distributed
 only using the hash distribution.

 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.

 balance-alb or 6

 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.

 Receive traffic from connections created by the server
 is also balanced. When the local system sends an ARP
 Request the bonding driver copies and saves the peer's
 IP information from the ARP packet. When the ARP
 Reply arrives from the peer, its hardware address is
 retrieved and the bonding driver initiates an ARP
 reply to this peer assigning it to one of the slaves
 in the bond. A problematic outcome of using ARP
 negotiation for balancing is that each time that an
 ARP request is broadcast it uses the hardware address
 of the bond. Hence, peers learn the hardware address
 of the bond and the balancing of receive traffic
 collapses to the current slave. This is handled by
 sending updates (ARP Replies) to all the peers with
 their individually assigned hardware address such that
 the traffic is redistributed. Receive traffic is also
 redistributed when a new slave is added to the bond
 and when an inactive slave is re-activated. The
 receive load is distributed sequentially (round robin)
 among the group of highest speed slaves in the bond.

 When a link is reconnected or a new slave joins the
 bond the receive traffic is redistributed among all
 active slaves in the bond by initiating ARP Replies
 with the selected MAC address to each of the
 clients. The updelay parameter (detailed below) must
 be set to a value equal or greater than the switch's
 forwarding delay so that the ARP Replies sent to the
 peers will not be blocked by the switch.

 Prerequisites:

 1. Ethtool support in the base drivers for retrieving
 the speed of each slave.

 2. Base driver support for setting the hardware
 address of a device while it is open. This is
 required so that there will always be one slave in the
 team using the bond hardware address (the
 curr_active_slave) while having a unique hardware
 address for each slave in the bond. If the
 curr_active_slave fails its hardware address is
 swapped with the new curr_active_slave that was
 chosen.

Now that we know the available modes, let’s create a new bonding interface named bond0 using mode 1 with eth0 and eth1 NICs.

# modprobe bonding mode=active-backup miimon=100
# ifconfig bond0 10.10.10.10 netmask 255.255.255.0 up
# ip link set eth0 master bond0
# ip link set eth1 master bond0

To make this tules persistent, use the following commands.

# cat <<EOF>> /etc/sysconfig/network-scripts/ifcfg-bond0
DEVICE=bond0
BOOTPROTO=static
ONBOOT=yes
IPADDR=10.10.10.10
NETMASK=255.255.255.0
BONDING_OPTS="mode=1 miimon=100"
EOF
# cat <<EOF>> /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
BOOTPROTO=none
ONBOOT=yes
MASTER=bond0
SLAVE=yes
EOF
# cat <<EOF>> /etc/sysconfig/network-scripts/ifcfg-eth1
DEVICE=eth1
BOOTPROTO=none
ONBOOT=yes
MASTER=bond0
SLAVE=yes
EOF
# cat <<EOF>> /etc/modprobe.d/bond.conf
alias bond0 bonding
EOF

If you need to check the bonding status, use the following command.

# cat /proc/net/bonding/bond0

If you need to switch the active NIC, use the following command.

# ifenslave -c bond0 eth1
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