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VxLAN – Think beyond VLAN for the Cloud!

We are familiar with VLAN (Virtual LAN) which segments a Layer-2 Network into subnetworks and hence limits the broadcast domain. There is a new (upcoming) IETF draft standard called VxLAN that seeks to replace VLAN in Cloud’s, Data Centers and other such large networks. Let us look at why a new standard might be required to extend VLAN, and some salient points about VxLAN, in this article.

Motivations behind VxLAN:

VLAN is the de-facto standard for LAN segmentation, but networks are becoming bigger every day. After the advent of Virtual Machines (Server Virtualization), hundreds of virtual machines can run in a single server, each with its own MAC address and VLAN group.

Current VLAN standard has a limitation of 4096 VLAN segments (max) in a network due to the 12-bit VLAN identifier used in it. Of course, its a huge number and most of the organizations may not require so many VLAN’s. But, when you consider a large data center running thousands of servers, with each server running many virtual machines within itself, there could be a requirement to exceed 4k VLAN’s (especially considering data centers hosting multiple tenants, each of whom want their network to be separated from others).

Private and public clouds too may require a large number of networks to be created within their infrastructure. Besides, when networks run protocols like STP (Spanning Tree Protocol) to prevent loops, a large network with a lot of VLAN’s induces a high degree of complexity and inefficient usage of links (as a lot of links may be disabled due to STP).

VxLAN and Salient points you need to know about VxLAN:

The full form of VxLAN is – Virtual eXtensible Local Area Network.

VxLAN is a new (proposed) IETF draft protocol which can be used to create up to 16 million segments in a network. This is possible because VxLAN uses a 24 bit identifier. So, networks using VxLAN can scale-up. VxLAN uses MAC-in-UDP encapsulation technique and runs on the IP Network. Moreover, when one VM wants to communicate with another VM (whose MAC address it does not know), VxLAN wraps an VxLAN header along with IP/UDP header and sends this message only to a particular IP Multicast group (which can access the destination VM).

Multicast is a better technique than broadcast and a lot of bandwidth is saved in the network, due to it. This is very critical in large networks where there are thousands of sub-networks to communicate with. VxLAN can work over Layer-2 networks, without the need for creating a Layer-3 network for IP routing. A Layer-2 network can be stretched across Layer-3 networks using VxLAN and hence it can work across multiple data centers and over large cloud networks. With VxLAN, logical networks can be extended to include VM’s / Servers belonging to different subnets.

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