Thursday, October 8, 2009

Network edge

InMon's quota controller brings together many of the topics that have been discussed on this blog, clearly illustrating the role of network-wide visibility in achieving effective control of the network.

The diagram shows the basic elements: a centralized sFlow analyzer receives sFlow data from every switch in the network, producing a real-time, network-wide view of traffic and accurately tracking the network topology. A centralized controller enforces management policies by automatically applying configuration settings to the edge switches in order to control traffic. For more information, see Controlling Traffic for a detailed description of InMon's controller and its application to peer-to-peer (P2P) traffic control.

Generally, this level of control is only possible because of the timely and complete picture of the network state that sFlow monitoring provides. In control engineering terms, sFlow makes the network observable; an essential prerequisite for control.

An accurate picture of the network state allows controls to be targeted where they will be most effective and have the least impact on other traffic; the edge of the network. The alternative, measurement and control at the network core, achieved at the core switches and routers, or by channeling traffic through shared control points (e.g. firewalls, traffic shapers, etc.), can result in serious performance problems as busy core devices become overloaded by additional measurement and control tasks. In addition, control at the core is ineffective if the traffic doesn't cross the core. On the other hand, all traffic crosses the edge and control at the edge is scalable since the number of edge devices grows with the network, providing additional measurement (sFlow) and control capacity as the network grows.

Interestingly, the centralized visibility into switched traffic that sFlow provides is being paralleled by a move toward centralized control of switches (see OpenFlow). The combination of centralized visibility and centralized control of network traffic paths has the potential to revolutionize data center networking, delivering the performance, scalability and control needed to build large, converged data centers.

In order to achieve visibility and control in the data center, it is essential to ensure that the edge is fully observable and controllable. Data center convergence is shifting the network edge to include components of blade servers and virtual servers. Finally, the Open vSwitch project is interesting because it will offer visibility (sFlow) and control (OpenFlow) at the edge of the virtualized data center (currently including support for Xen/XenServer, KVM, and VirtualBox).

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