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This illustration shows how, when configured in Active-active mode, the links that are active in bonds vary
according to traffic type. In the top picture of a management network, NIC 1 is active and NIC 2 is passive. For
the VM traffic, both NICs in the bond are active. For the storage traffic, only NIC 3 is active and NIC 4 is passive.
XenServer load balances the traffic between NICs by using the source MAC address of the packet. Because, for
management traffic, only one NIC in the bond is used, active-active mode does not balance management traffic.
API Management traffic can be assigned to a XenServer bond interface and will be automatically load-balanced
across the physical NICs.
Re-balancing is provided by the existing ALB re-balance capabilities: the number of bytes going over each slave
(interface) is tracked over a given period. When a packet is to be sent that contains a new source MAC address it
is assigned to the slave interface with the lowest utilization. Traffic is re-balanced every 10 seconds.
Active-active mode is sometimes referred to as Source Load Balancing (SLB) bonding as XenServer uses SLB to
share load across bonded network interfaces. SLB is derived from the open-source ALB mode and reuses the ALB
capability to dynamically re-balance load across NICs.
Note:
Active-active bonding does not require switch support for Etherchannel or 802.3ad (LACP).
Active-Passive Bonding
Active-Passive bonding:
• routes traffic over only one of the NICs in the bond
• will failover to use the other NIC in the bond if the active NIC loses network connectivity
• can be configured with one fast link and one slow path for cost savings. In this scenario, the slow path should
only be used if there is a failure on the fast path
• does not require switch support for Etherchannel or 802.3ad(LACP)
• is derived from the open source Active-Backup mode
As active-active mode is the default bonding configuration in XenServer, you must configure active-passive mode
if you want to use it. You do not need to configure active-passive mode just because a network is carrying
management traffic or storage traffic. When bonds are configured or left as active-active mode and XenServer
detects management or storage traffic, XenServer automatically leaves one NIC in the bond unused. However,
you can explicitly configure active-passive mode, if desired.
When trying to determine when to configure active-passive mode, consider configuring it in situations such as
the following:
• When you are connecting one NIC to a switch that does not work well with active-active bonding.
For example, if the switch does not work well, you might see symptoms like packet loss, an incorrect ARP table
on the switch. Likewise, the switch would not update the ARP table correctly and/or the switch would have
incorrect settings on the ports (you might configure aggregation for the ports and it would not work).
• When you do not need load balancing or when you only intend to send traffic on one NIC.
For example, if the redundant path uses a cheaper technology (for example, a lower-performing switch or
external up-link) and that results in slower performance, configure active-passive bonding instead.
Note:
As of XenServer 6.0, the vSwitch supports active-passive NIC bonding. If you are using the
vSwitch as your networking configuration, you can set the bonding mode to active-passive
(also known as active-backup) using the XenCenter or the CLI.