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FEATURE DATA CENTRES


aggregation, and core switches. Te newer applications generate significant traffic between servers and between virtual machines, requiring flatter, less tiered architectures to accommodate the greater horizontal ‘east-west’ traffic. ‘Tese workloads are not predictable; as an


administrator, you can’t figure out how much east-west traffic there is,’ says Arpit Joshipura, vice


The industry has been looking elsewhere to tackle communications challenges


president, product management and marketing at Dell Networking. ‘What you want is an agile network to respond to these workloads in real time and without human intervention.’ It is not only virtualised servers that generate


east-west traffic. Te large Web 2.0 companies – Facebook, Google and the like with their hyperscale data centres – use dedicated servers that generate considerable horizontal traffic. Ultimately, what customers want is a certain


functionality that enables a virtual machine to talk with other virtual machines, whether they are on


the same server, on different servers in a data centre, or on servers in different data centres. Segregating and managing the increasing


number of workloads in the data centre using traditional layer 2 networking mechanisms such as virtual LANs (VLANs) has created management and scale issues. VLANs are widely used but are limited to 4,096 per domain. Te need to manage and provision multiple customers’ workloads and virtual machines across many domains has become burdensome.


Embracing new approaches Te industry has been looking elsewhere to tackle the communications challenges, and this has led to interest in SDN. Initially associated with OpenFlow, SDN has come to be viewed more as an architectural framework than a technology. Switches and routers in traditional networks


communicate among themselves to determine the required links. SDN does away with such distributed control, favouring a centralised view and a decoupling of the control and data planes. Te result is a soſtware component – comprising one or more programs – that sits outside the network and controls a portion of it. ‘Tis soſtware entity controls how the network behaves, how it is provisioned, and how it forwards traffic from one part of the network to another,’ says Terpstra. Network virtualisation is one approach that has emerged to address the data centre’s networking


NETWORK VIRTUALISATION


Network virtualisation is still a new technology, with deployments only beginning in the last year. ‘Network virtualisation today is where server virtualisation was three or four years ago,’ says Nuage’s Modarres. ‘It [network virtualisation]


maintains the same virtual environment that exists in servers so that it can be projected across the network to other servers,’ says Nick Ilyadis, CTO infrastructure and networking group at Broadcom. Broadcom makes the


StrataXGS Trident II Ethernet switch family, adopted by several switch vendors including Cisco,


which has hardware support for network virtualisation. Several elements are


used for network virtualisation. The management or policy software, the controller, overlay protocols and the hypervisor’s virtual switch. The virtual switch connects virtual machines to the network, while the controller maintains the configuration state of the network. ‘Layer 2 and Layer 3 connectivity, and Layer 4 through 7 services associated with the workloads; all that is maintained in the controller,’ says VMware’s King. The controller also


implements the changes when connectivity is required. Meanwhile, the management engine sets policy, the rules associated with workloads that are enacted by the controller. An overlay establishes


the connectivity between hypervisors. Three overlay protocols are commonly used to create tunnels across the network: Virtual Extensible LAN (VXLAN), Network Virtualization using Generic Routing Encapsulation (NVGRE), and Stateless Transport Tunnelling (STT). In addition, some vendors also have proprietary overlay schemes. ‘It [network virtualisation]


is agnostic to the underlying physical network,’ says IDC’s Casemore. ‘The only thing it uses that networking for is simple IP forwarding.’ That works fine when the IT environment is virtualised. But to accommodate workloads on dedicated servers, a virtual tunnel end point (VTEP) in needed. The VTEP is a gateway between the physical and virtual worlds, and can translate between the different overlay protocols. ‘Network virtualisation


gives the data centre operator a very easy handle by which to manage the traffic,’ says Ilyadis. The overlay separates customer traffic and uses identifiers


that define how traffic is treated. ‘You don’t have to provide traffic management, policing and service assurance by looking at individual MAC addresses or IP packets,’ says Ilyadis. The biggest benefit of


network virtualisation is workload expansion, by simplifying the creation of virtual machines and their connectivity. ‘All the attributes of that network now exist as opposed to having to recreate them manually,’ says Ilyadis. ‘It sounds easy but when you have thousands of customers, automating a particular session buys you a lot of leverage.’


challenges. It embraces SDN’s soſtware entity concept, using a controller to oversee the network. Te controller knows the connectivity, and effects change using an overlay network on top of the physical network. ‘You provide an abstraction layer and you do


networking on top of that layer rather than do things to touch the hardware natively,’ says Chris King, vice president, product marketing, networking and security business unit at VMware. ‘Te implication of that is that you have to faithfully reproduce the entire network in that abstraction, so that the applications riding on top of it are unaware they are not touching the hardware.’ Network virtualisation simplifies and speeds up


network provisioning (see box). Once the physical network is set up, the overlay takes care of connecting the data centre resources, enables automation and reduces provisioning times. Te abstraction layer, by decoupling from the underlying physical network, promises a further benefit. ‘It means I refresh my hardware when I need to refresh my hardware, not when I need new features,’ says King. ‘Tat is truly disruptive.’ VMware with its NSX network virtualisation


and security platform is working with several switch vendors including Arista Networks, Brocade, Cumulus, Dell, HP, and Juniper. Another proponent of network virtualisation is Nuage Networks, Alcatel-Lucent’s spin-in company, with its Virtualised Services Platform soſtware.


Issue 3 • Spring 2014 FIBRE SYSTEMS 15


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