Microsoft_Press_ebook_Introducing_Windows_Server_2012_R2_PDF.pdf

116 chapter 5 networking drivers called extensions to

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116 CHAPTER 5 Networking drivers (called extensions ) to be added to the driver stack of the virtual switch. This means that networking independent software vendors (ISVs) can create extensions that can be installed in the virtual switch to perform different actions on network packets being processed by the switch. The Hyper-V Extensible Switch supports three kinds of extensions: Capturing extensions These can capture packets to monitor network traffic but cannot modify or drop packets. Filtering extensions These are like capturing extensions but also can inspect and drop packets. Forwarding extensions These allow you to modify packet routing and enable integration with your physical network infrastructure. The Hyper-V Extensible Switch also lets you use the built-in Wfplwfs.sys filtering extension of the Windows Filtering Platform (WFP) to intercept packets as they travel along the data path. Networking ISVs can use this functionality to develop applications that can perform packet inspection on a virtual network. In Windows Server 2012, however, the Hyper-V Extensible Switch was layered above Hyper-V Network Virtualization functionality as shown on the left in Figure 5-9. This meant that capturing, filtering, or forwarding extensions installed in the switch could only see the CA packets, that is, the packets that the virtual machine sees on its virtual network. The extensions could not see or manipulate the PA packets, that is, the packets that the Hyper-V host sees on the hosting provider’s underlying physical network. However, in Windows Server 2012 R2 network virtualization, functionality now resides in the Hyper-V Extensible Switch, as shown on the right in Figure 5-8. This means that third-party extensions can now process network packets using either CA or PA addresses as desired. This enables new types of scenarios, such as hybrid forwarding, whereby Hyper-V Network Virtualization forwards the network virtualization traffic while a third-party extension forwards non-network virtualization traffic. Another possibility might be a networking ISV developing a firewall application that drops certain kinds of packets on the customer’s network and other types of packets on the provider’s network. It also allows third-party ISVs to use the Hyper-V Extensible Switch to implement their own network virtualization solutions using Hyper-V instead of needing to use the in-box Hyper-V Network Virtualization approach from Microsoft. Finally, if you wanted to implement a network virtualization solution using Hyper-V in Windows Server 2012, you needed to use third-party gateway products to do this. That’s because Windows Server 2012 doesn’t include an in-box gateway, and a gateway is needed to provide connectivity between virtual machines running on the virtual network and resources on physical networks at local or remote sites. The result is that Hyper-V Network Virtualization by itself in Windows Server 2012 creates virtual subnets that are separated from the rest of the network the way islands are separated from the mainland.
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