XenServer uses physical interfaces (PIFs) and virtual interfaces (VIFs) to connect virtual machines to networks. There are different types of networks like private, external, and bonded networks. External networks connect VMs to the physical network through a bridge. The XenServer hypervisor handles VM traffic by forwarding packets to the virtual switch which determines the destination VIF and passes the packet to the VM. Management interfaces are used for controlling XenServer and live migrations. Bonds aggregate multiple NICs and VLANs segregate traffic using separate bridges.

1. XENSERVER NETWORKING
Asrar Kadri

2. XENSERVER NETWORKING
• XenServer Networking Terminology
• Types of Networks
• How XenServer Handles VM traffic
• Management Interface
• Bonds and VLANs

3. XenServer Networking Terminology
PIF: This is the object name for a physical network interface. XenServer is based on linux.
This means each physical network interface will get the normal linux
name ethX. XenServer will create a PIF object and assigned to each ethXdevice. Each PIF
will get his unique ID, uuid, to give him an internal identifier.
VIF: Virtual machines connect to networks using virtual NICs, known as
virtual interfaces. Virtual interfaces let VMs send and receive network traffic. You can
assign each virtual interface its own IP address and MAC address.
Network: A network is actually a virtual Ethernet switch with bridging functionality. The
switch will get a uniqie uuid and name. The basic virtual switch that you will get with a
standard XenServer installation acts like a simple physical switch and allows to connect
virtual machines to it via their VIF. A virtual switch can provide an uplink via a PIF to
create an external network.

4. TYPES OF NETWORKS
• Single-Server Private networks have no association to a physical network interface
and can be used to provide connectivity between the virtual machines on a given
host, with no connection to the outside world.
• Cross-Server Private networks extend the single server private network concept
to allow VMs on different hosts to communicate with each other by using the vSwitch.
• External networks have an association with a physical network interface and
provide a bridge between a virtual machine and the physical network interface
connected to the network.
• Bonded networks create a bond between two NICs to create a single, high-
performing channel between the virtual machine and the network.

5. VIFs and External Bridge
Here we can see nine bridges ( xenbr0 – xenbr9). Xenserver creates a virtual bridge
for each PIF attached to the server. The VIFs are connected to xenbr2, which
provides external connectivity

6. How XenServer Handles VM Traffic • The physical NIC is in
promiscuous mode;
which means that it
would accept all the
packets flowing on the
wire.
• The packet is forwarded
to the Virtual switch
xenbr0
• The switch would look
at the destination MAC
address and find the
VIF to which it is
connected.
• Once the VIF is
determined, the
Xenserver then passes
it to the Virtual
Machine

7. MANAGEMENT INTERFACE
• Defined during Xenserver installation
• Used to control Xenserver via XenCenter
• Also used during Live Migration and communication between the hosts in a
Resource Pool
• Putting the management interface on a VLAN network is not supported

8. If this PIF is also being used as the management port, an IP address needs to be assigned.
In this case it’s actually the bridge that has the IP address, not the PIF. Any
packet that’s destined for the management IP address will be processed by the bridge,
and then the host OSI layers, since the MAC destination on that frame will be that of the
bridge. The PIF won’t process the IP packet, since it doesn’t have an IP address assigned.
MANAGEMENT INTERFACE

9. Bonds and VLANS
BONDS
Technique where two or more NICs are configured together to logically function as
one. Used for redundancy and Throughput aggregation
Active-backup : Only one NIC would be actively used for traffic and only in case of its
failure would an inactive NIC take over
Balance-slb (active-active): Traffic load balancing based on the source MAC address of
each Virtual Network Interface (VIF) of a guest.

10. VLANs
• To segregate production and development traffic
• For each VLAN, a separate bridge is created
• VLAN configuration is transparent to the guest VM. Tagging/untagging is taken care
by the kernel.

11. RESOURCES
> Understanding XenServer Networking - The Linux Perspective
http://support.citrix.com/article/CTX117915
> XenServer VLAN Networking :
http://support.citrix.com/article/CTX123489
> How to Configure Network and Bonds for XenServer
http://support.citrix.com/article/CTX132002