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together so they logically function as one network card. Both NICs have the same MAC address and, in the case
of management interfaces, have one IP address.
If one NIC in the bond fails, the host's network traffic is automatically redirected through the second NIC. NIC
bonding is sometimes also known as NIC teaming. XenServer supports up to eight bonded networks. You can
bond two NICs together of any type (management interfaces or non-management interfaces).
In the illustration that follows, the primary management interface is bonded with a NIC so that it forms a bonded
pair of NICs. XenServer will use this bond for management traffic.
This illustration shows three pairs of bonded NICs, including the primary
management interface. Excluding the Primary Management Interface bond,
XenServer uses the other two NIC bonds and the two un-bonded NICs for VM traffic.
Specifically, you can bond two NICs together of the following types:
•Primary management interfaces. You can bond a primary management interface to another NIC so that the
second NIC provides failover for management traffic. However, NIC bonding does not provide load balancing
for management traffic.
•NICs (non-management). You can bond NICs that XenServer is using solely for VM traffic. Bonding these NICs
not only provides resiliency, but doing so also balances the traffic from multiple VMs between the NICs.
•Other management interfaces. You can bond NICs that you have configured as management interfaces (for
example, for storage). However, for most iSCSI software initiator storage, Citrix recommends configuring
multipathing instead of NIC bonding since bonding management interfaces only provides failover and not load
balancing.
It should be noted that certain iSCSI storage arrays, such as Dell EqualLogic, require using bonds.
NIC bonds can work in either an Active/Active mode, with VM traffic balanced between the bonded NICs, or in
an Active/Passive mode, where only one NIC actively carries traffic.
XenServer NIC bonds completely subsume the underlying physical devices (PIFs). To activate a bond, the
underlying PIFs must not be in use, either as the primary management interface for the host or by running VMs
with VIFs attached to the networks associated with the PIFs.
In XenServer, NIC bonds are represented by additional PIFs, including one that represents the bond itself. The
bond PIF can then be connected to a XenServer network to allow VM traffic and host management functions to
occur over the bonded NIC. The exact steps to create a NIC bond depend on the number of NICs in your host and
whether the primary management interface of the host is assigned to a PIF to be used in the bond.
Provided you enable bonding on NICs carrying only guest traffic, both links are active and NIC bonding can balance
each VM’s traffic between NICs. Likewise, bonding the primary management interface NIC to a second NIC also
provides resilience. However, only one link (NIC) in the bond is active and the other remains unused unless traffic
fails over to it.
If you bond a management interface, a single IP address is assigned to the bond. That is, each NIC does not have
its own IP address; XenServer treats the two NICs as one logical connection.