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Virtual Extensible LAN [VXLAN] specification was originally created by VMware,Arista Networks and Cisco. Other backers of the VXLAN technology include Citrix,Dell,Redhat,Juniper Networks and more.VXLAN is used in configuring network topology for cloud service providers and enterprise data centers.

VXLAN supports scalability across multi-tenant networks.Each tenant requires its own logical network, which in turn, requires its own network identification (network ID). Traditionally, network engineers have used virtual LANs to isolate tenant networks but VLAN specifications only allow for up to 4,096 network IDs to be assigned at any given time which may not be enough addresses for a public computing environment.

VXLAN transfers virtual resources across shared cloud infrastructures both within and across datacenters.This improved mobility will ultimately enable better approaches to load balancing, disaster recovery, power-usage optimization, datacenter provisioning and migration, and other challenges approaching us in the cloud era.

The primary goal of VXLAN is to extend the virtual LAN (VLAN) address space by adding a 24-bit segment ID and increasing the number of available IDs to 16 million. The VXLAN segment ID in each frame differentiates individual logical networks so millions of isolated Layer 2 VXLAN networks can co-exist on a common Layer 3 infrastructure. As with VLANs, only virtual machines within the same logical network can communicate with each other.

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Fig1.VXLAN Header Format

Advantages

Extremely scalable for deploying large number of isolated networks for large number of cloud service deployment.It increases scalability up to 16 million logical networks and allows for layer 2 adjacency across IP networks.

VXLAN can improve the throughput and latency of the networking system.VXLAN is designed to be pretty efficient. Most server-grade NICs have offloading for VLAN tagging. The newer ones are also implementing offloading for VXLAN so if you have a NIC that supports VXLAN offload then there should be almost no performance hit.

Disadvantages

A logical subnet using VXLAN encapsulation cannot communicate with the physical devices such as switches, load balancers or firewalls, although one would expect some data center switch vendors to implement Layer 3 VXLAN termination support.
Multicast required end to end

Before enabling VXLAN

The frame size of VXLAN is generally larger(Jumbo Frames) than the ordinary frames.The 50 byte overhead created by VXLAN clearly takes the frame size over the standard Ethernet MTU of 1500 (not counting the Ethernet headers of the VXLAN frame) which means,in order to use VXLAN we really need Jumbo Frames supported on the network connecting the Virtual Tunnel End Points (VTEP).

In my next article I will focus on how to configure VXLAN in openstack neutron.
Hope you found this post informative..
Thank you..

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