Tunneling Technologies for the Data Center

Tunneling Technologies for the Data Center:

These tunneling methods are

• Virtual eXtensible Local Area Network (VXLAN) [3], 
• Network Virtualization using Generic Routing Encapsulation (NVGRE) [4]
• Stateless Transport Tunneling (STT)

Virtual eXtensible Local Area Network (VXLAN)

The VXLAN technology was developed primarily by VMware and Cisco as a means to mitigate the

inflexibility and limitations of networking technologySome of the main characteristics of VXLAN are:

• VXLAN utilizes MAC-in-IP tunneling
• Each virtual network or overlay is called a VXLAN segment.
• VXLAN segments are identified by a 24-bit segment ID, allowing for up to 224 (approximately
• 16 million) segments.
• VXLAN tunnels are stateless.
• VXLAN segment endpoints are the switches that perform the encapsulation and are called virtual tunnel endpoints (VTEPs).
• VXLAN packets are unicast between the two VTEPs and use UDP-over-IP packet formats.
• It is UDP based. The UDP port number for VXLAN is 4789

Network Virtualization using Generic Routing Encapsulation (NVGRE)

The NVGRE technology was developed primarily by Microsoft, with other contributors including Intel,

Dell, and Hewlett-Packard. Some of the main characteristics of NVGRE are:

• NVGRE utilizes MAC-in-IP tunneling.
• Each virtual network or overlay is called a virtual layer two network.
• NVGRE virtual networks are identified by a 24-bit virtual subnet identifier, allowing for up to 22 (16 million) networks.
• NVGRE tunnels, like GRE tunnels, are stateless.
• NVGRE packets are unicast between the twoNVGRE end points, each running on a switch.NVGR utilizes the header format specified by the GRE standard [11,12].

Stateless Transport Tunneling (STT)

Stateless Transport Tunneling (STT) is a recent entry into the field of tunneling technologies used for network virtualization. Its major sponsor was originally Nicira. Some of the main characteristics of STT are:

• STT utilizes MAC-in-IP tunneling.
• The general idea of a virtual network exists in STT but is enclosed in a more general identifier called a context ID.
• STT context IDs are 64 bits, allowing for a much larger number of virtual networks and a broader range of service models.
• STT attempts to achieve performance gains over NVGRE and VXLAN by leveraging the TCP Segmentation Offload (TSO) found in the network interface cards (NICs) of many servers. TSO is a mechanism implemented on server NICs that allows large packets of data to be sent from the server to the NIC in a single send request, thus reducing the overhead associated with multiple smaller requests.
• STT, as the name implies, is stateless.
• STT packets are unicast between tunnel end points, utilizing TCP in the stateless manner associated with TSO. This means that it does not use the typical TCP windowing scheme, which requires state for TCP synchronization and flow control.

SDN Use Cases in the Data Center