About XenServer Networks

Each managed server has one or more networks. A XenServer network is a virtual Ethernet switch that may be connected to an external interface (with or without a VLAN tag) or may be entirely virtual, internal to an individual server or pool.

When XenServer is installed on a physical server, a network is created for each physical NIC on the server. The network works as a bridge between a virtual network interface on a Virtual Machine (VIF) and a physical network interface (PIF) associated with a network interface card (NIC) on the host server.

When you move a managed server into a Resource Pool, these default networks are merged so that all physical NICs with the same device name are attached to the same network. Typically, you would only need to add a new network if you wished to create an internal network, to set up a new VLAN using an existing NIC, or to create a NIC bond. You can configure up to 16 networks per managed server, or up to 8 bonded network interfaces.

Jumbo frames can be used to optimize performance of storage traffic. You can set the Maximum Transmission Unit (MTU) for a new server network in the New Network wizard or for an existing network in its Properties window, allowing the use of jumbo frames. The possible MTU value range is 1500 to 9216.

Network types

There are four different physical (server) network types to choose from when creating a new network within XenCenter.

Single-Server Private network

This is an internal network that has no association with a physical network interface, and provides connectivity only between the virtual machines on a given server, with no connection to the outside world.

Cross-Server Private network

This is a pool-wide network that provides a private connection between the VMs within a pool, but which has no connection to the outside world. Cross-server private networks combine the isolation properties of a single-server private network with the ability to span a resource pool. This enables use of VM agility features such as XenMotion live migration and Workload Balancing (WLB) for VMs with connections to cross-server private networks. VLANs provide similar functionality though unlike VLANs, cross-server private networks provide isolation without requiring configuration of the physical switch fabric, through the use of the Generic Routing Encapsulation (GRE) IP tunneling protocol. To create a cross-server private network, the following conditions must be met:

  • all of the servers in the pool must be using Open vSwitch for networking;
  • the pool must have a vSwitch Controller configured that handles the initialization and configuration tasks required for the vSwitch connection (this must be done outside of XenCenter).

External network

This type of network has an association with a physical network interface and provides a bridge between virtual machines and your external network, enabling VMs to connect to external resources through the server’s physical network interface card.

Bonded network

This type of network is formed by bonding two or more NICs to create a single, high-performing channel that provides connectivity between VMs and your external network. Three bond modes are supported:

  • Active-active - In this mode, traffic is balanced between the bonded NICs. If one NIC within the bond fails, all of the host’s network traffic automatically routes over the second NIC. This mode provides load balancing of virtual machine traffic across the physical NICs in the bond.
  • Active-passive (active-backup) - Only one NIC in the bond is active; the inactive NIC becomes active if and only if the active NIC fails, providing a hot-standby capability.
  • Link Aggregation Control Protocol (LACP) Bonding - This mode provides active-active bonding, where traffic is balanced between the bonded NICs. Unlike the active-active bond in a Linux bridge environment, LACP can load balance all traffic types. Two available options in this mode are:
    • LACP with load balancing based on source MAC address - In this mode, the outgoing NIC is selected based on the MAC address of the VM from which the traffic originated. Use this option to balance traffic in an environment where you have several VMs on the same host. This option is not suitable if there are fewer VIFs than NICs: as load balancing is not optimal because the traffic cannot be split across NICs.
    • LACP with load balancing based on IP and port of source and destination - In this mode, the source IP address, the source port number, the destination IP address, and the destination port number are used to route the traffic across NICs. This option is ideal to balance traffic from VMs and the number of NICs exceeds the number of VIFs. For example, when only one virtual machine is configured to use a bond of three NICs.


  • You must configure vSwitch as the network stack to be able to view the LACP bonding options in XenCenter and to create a new LACP bond. Also, your switches must support the IEEE 802.3ad standard.
  • Active-active and active-passive bond types are available for both the vSwitch and Linux bridge.
  • You can bond either two, three, or four NICs when vSwitch is the network stack, whereas you can only bond two NICs when Linux bridge is the network stack.

For more information about the support for NIC bonds in XenServer, see the XenServer Administrator’s Guide.

About XenServer Networks

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