What’s New in Windows 8 for Hyper-V Based Cloud Computing (Part 8) – Hyper-V Networking Features

If you would like to read the other parts in this article series please go to:

Windows Server 2012 and Multi-Tenant Clouds         

Many of the networking features in Windows Server 2012 are critical enablers for the deployment of multi-tenant private and public clouds, as much in terms of functionality as performance. Whether deploying new workloads or migrating existing workloads into a cloud infrastructure, these must be quickly deployed and running in the cloud without the need for extensive network reconfiguration. Once in the cloud, it is also necessary to ensure the secure network isolation of workloads along organizational or individual virtual machines. The cloud infrastructure must also provide a wide array of network technologies to support and scale the workload network performance and adapt to resource requirements changes. Finally, the cloud infrastructure must provide network management tools that integrate seamlessly across the spectrum of workload operations to support flexible and scalable operational models. Windows Server 2012 addresses all these areas, allowing the creation of dynamic and performing cloud infrastructures in a wide range of enterprise scenarios.

Network Virtualization

One of the promises of a cloud infrastructure is the ability to quickly and easily deploy new workloads or migrate workloads running on physical servers or other cloud infrastructures. While a new workload deployment may not pose a great network configuration challenge, the story is a little different when considering the migration of existing workloads running on physical servers or VMs migrated from other cloud infrastructures. Windows Server 2012 addresses this issue with a feature called network virtualization. In a nutshell, network virtualization provides a hypervisor-level mapping between the network address assigned inside a virtual machine (Customer Address or CA) and a unique host-based network address (Provider Address or PA) which is used to route the packets on the physical networks. There are two network virtualization mechanisms supported in Windows Server 2012, namely the Generic Routing Encapsulation (GRE) protocol and IP Rewrite. On the source host, GRE encapsulates the IP packet from the VM containing the source and destination CAs with a new header that uses source and destination PAs to enable routing of the packet through the network fabric. The GRE header provides a key field or Virtual Subnet ID that allows multiple VMs running on a host to share a single PA. This is similar to the use of a VLAN tag to ensure network traffic isolation. The Virtual Subnet ID is represented by a 24 bit identifier that allows more than 16 million unique values. On the destination host, the Virtual Subnet ID along with the PA to CA mapping is used to deliver the packet to the intended VM. The drawback to using GRE is that the physical network components in the underlying infrastructure must support GRE. If not, network offloads technologies will not function, and GRE packets cannot be processed. In the case where host and physical network components do not support GRE, there is the option to use IP Rewrite to leverage network virtualization. In this scenario, the source and destination CAs are replaced with the appropriate PAs based on the information in the mapping table, before placing the packet on the physical network. However, each CA must be associated with a unique PA, negating the advantage of sharing a single PA among multiple VMs.

Networking Technologies

Following the ease of deployment of workloads in a cloud infrastructure comes the necessity to provide highly scalable and reliable compute, storage, and network performance. Windows Server 2012 delivers high-performance networking for cloud infrastructures through a set of protocols and technologies that address network congestion, quality of service, and network offloads.

In Windows Server 2012, Datacenter TCP (DCTCP) helps to manage network traffic congestion without relying on high-priced switches to mitigate the issue. Instead, DCTCP acts on Explicit Congestion Notification (ECN) bits generated by switches to detect network congestion and reacts by throttling data flow to avoid over-subscription of the network pipes. Windows Server 2012 intelligently enables DCTCP on low latency, fast network links with low round trip times. At the network adapter level, Windows Server 2012 provides Datacenter Bridging (DCB) to address congestion by applying bandwidth reservations based on traffic types. In addition, Windows Server 2012 can also address congestion in the network stack by offloading network data transfers to the network adapter through Remote Direct Memory Access (RDMA). RDMA involves writing data directly to the network adapter which takes over the processing of the data transfer, offloading and reducing the host CPU utilization.

One of the network offload technologies found in Windows Server 2012 is Single Root I/O Virtualization (SR-IOV). SR-IOV allows network data transfers directly between VMs and network adapters, reducing the host CPU utilization, and increasing network throughput through lower latency. SR-IOV requires support from both the host and network adapter as well as requiring processor hardware virtualization support. One of the drawbacks to using an SR-IOV aware network adapter is that it is excluded from participating in NIC teaming for the simple reason that the network data transfer using SR-IOV bypasses the host virtual switch stack which manages NIC teaming.

Another network offload technology in Windows Server 2012 is Receive Segment Coalescing (RSC). RSC provides for the aggregation of smaller received network packets that arrive within a single interrupt cycle into a larger packet (with a maximum size of 64K). This helps to reduce the amount of packet header processing that the host must perform. Receive Side Scaling (RSS) enables network adapters to distribute the network processing load across multiple processor cores instead of a single processor core. In Windows Server 2012, RSS is enhanced to support non-TCP traffic, better scalability across Non-Uniform Memory Access (NUMA) nodes, and optimization for support of hosts with more than 64 processors to achieve highly scalable configurations. Finally, dynamic Virtual Machine Queues (VMQ), which allows network adapters to create virtual network queues for each VM on a host, is also enhanced in Windows Server 2012 to support reassigning available queues based on the changing network traffic requirements of VMs.

NIC Teaming

Windows Server 2012 provides a native NIC teaming feature that is vendor agnostic and supports up to 32 network adapters, NIC teaming using different models of network adapters from different vendors, bandwidth aggregation and failover configurations, and unlimited virtual interfaces. NIC teaming supports switch independent and switch dependent modes (static teaming or dynamic teaming with Link Access Control Protocol). When NIC teaming is configured for bandwidth aggregation, load distribution across the NIC teams is accomplished using either an address hash (IP address and TCP port number), or by specifying a Hyper-V port to ensure that the network traffic for a particular VM flows through a specific network adapter.

PowerShell Network Management

Windows Server 2012 provides graphical network management tools, but also a robust command line based management approach through PowerShell 3.0 and WMIv2. Using PowerShell 3.0, all aspects of Windows Server 2012 management can be automated. Windows Server 2012 includes more than 2000 cmdlets to automate not only networking, but also storage, clustering, RDS, DHCP, DNS, File Servers, Print, and the list goes on. In terms of network management, PowerShell 3.0 provides cmdlets to manage TCP/IP settings, network adapters, network connectivity and policy, network load balancing, network QOS, and NIC teaming.


In this article, you learned about the new networking features in Windows Server 2012 that support cloud deployments. In Part 9 of this series, you will learn about cloud network scenarios that Microsoft supports with Windows Server 2012.

If you would like to read the other parts in this article series please go to:

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