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