Open vSwitch

(diagram from Open vSwitch)

The Open vSwitch provides advanced switching capabilities for virtual servers. Currently the Open vSwitch supports Linux, Xen/XenServer, KVM and Virtual Box. The open source software is designed to be easily portable and is expected to support additional platforms in the future. The Open vSwitch is designed to integrate switching across multiple physical servers, providing an open source alternative to proprietary virtual switches such as VMWare's distributed switch and Cisco's Nexus 1000v.

The recent integration of sFlow traffic monitoring in the Open vSwitch extends the visibility into virtual servers, ensuring data center visibility and control.

Note: The Open vSwitch demonstrates how to integrate the reference sFlow agent code with a virtual switch or network adapter. Integrating sFlow requires minimal support in the "fast path" requiring only packet sampling and packet counters.

The following lines, added to the Open vSwitch configuration file (ovs-vswitchd.conf), configure sampling packets at 1-in-512, polling counters every 20 seconds and sending sFlow to an analyzer (10.0.0.50) over UDP using the default sFlow port (6343):

sflow.<bridgename>.agent    = eth0
sflow.<bridgename>.host     = 10.0.0.50:6343
sflow.<bridgename>.sampling = 512
sflow.<bridgename>.polling  = 20
sflow.<bridgename>.header   = 128

Note: Type "man ovs-vswitchd.conf" for a full list of configuration options. A previous posting discussed the selection of sampling rates.

The following screen capture, from the free sFlowTrend application, demonstrates the visibility provided by sFlow in the Open vSwitch:

All traffic is visible, traffic between virtual machines, and from the virtual machines to the outside world. In addition, sFlow is able to report on all the protocols on the network (note the layer 2, TCP and IPv6 flows in the chart), as well as information on VLANs and layer 2 priorities that is essential for managing switched traffic.

The second screen capture shows a bandwidth trend for a virtual adapter on the vSwitch:

This type of interface trending is a staple of network management, but obtaining the information is challenging in virtual environments. While SNMP is typically used to obtain this information from network equipment, servers are much less likely to be managed using SNMP and so SNMP polling is often not an option. In addition, there may be large numbers of virtual ports associated with each physical switch port. In a virtual environment with 10,000 physical switch ports you might need to monitor as many as 200,000 virtual ports. Even if SNMP agents were installed on all the servers, SNMP polling does not scale well to large numbers of interfaces. The integrated counter polling mechanism built into sFlow provides scalable monitoring of the utilization of every switch port in the network, both physical and virtual, quickly identifying problems wherever they may occur in the network.

Download Open vSwitch and sFlowTrend to evaluate the benefits of visibility in the virtualization layer.

Finally, the Open vSwitch also supports the OpenFlow to allow centralized control of switch forwarding. The combination of sFlow and OpenFlow in the vSwitches delivers visibility and control of the network edge.

Feb. 15, 2011 Update: The configuration steps shown in this article are no longer correct, more recent versions of the Open vSwitch use the ovs-vsctl command instead. The easiest way to manage the sFlow configuration of an Open vSwitch is to install the open source Host sFlow agent which will automatically manage sFlow settings in the Open vSwitch. For recent information on the Open vSwitch, click on the vSwitch label below.