Complete guide to network virtualization

With new proposed standards, virtualization is moving from the server world to the network itself

There are a number of emerging and proposed standard protocols focused on optimizing the support that data center Ethernet LANs provide for server virtualization. Several of these protocols are aimed at network virtualization via the creation of multiple virtual Ethernet networks that can share a common physical infrastructure in a manner that is somewhat analogous to multiple virtual machines sharing a common physical server.

Most protocols for network virtualization are based on creating virtual network overlays using techniques based on encapsulation and tunneling. The most commonly discussed protocols include VXLAN, NVGRE, STT, and SPB MAC-in-MAC. SPB is already an IEEE standard, while it is likely that only one of the other proposals will achieve IETF standard status, most likely VXLAN.

Traditional network virtualization

The one-to-many virtualization of network entities is not a new concept. The most common examples are VLANs and Virtual Routing and Forwarding (VRF) instances.

VLANs partition the network into as many as 4,094 broadcast domains, as designated by a 12-bit VLAN ID tag in the Ethernet header. VLANs have been a convenient means of isolating different types of traffic that share the same switched LAN infrastructure.

In data centers that make extensive use of server virtualization, the limited number of VLANs can present problems, especially when large number of tenants need to be supported, each requiring multiple VLANs. Extending VLANs across the data center via 802.1Q trunks to support VM mobility adds operational cost and complexity. In data centers based on Layer 2 server-to-server connectivity, large numbers of VMs, each with its own media access control address, can also place a burden on the forwarding tables capacities of Layer 2 switches.

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