VXLAN (Virtual eXtensible LAN) is an ‘overlay’ technology introduced a couple of years ago to solve the challenges associated with VLAN scalability and to enable the creation of a large number of logical networks (up to 16 million). It also has the benefit of allowing layer 2 segments to be extended across layer 3 boundaries due to the MAC-in-UDP encapsulation used.

One of the most significant barriers to the deployment of VXLAN is its reliance upon IP multicast in the underlying network for handling of broadcast / multicast / unknown unicast traffic – many organisations simply do not run multicast today and have no desire to enable it on their network. Another issue is that while VXLAN itself can support up to 16 million segments, it is not feasible to support such a huge number of multicast groups on any network – so in larger scale VXLAN environments, multiple VXLAN segments might have to be mapped to a single multicast group, which can lead to flooding of traffic where it is not needed or wanted.

With the release of version 4.2(1)SV2(2.1) of the Nexus 1000V, Cisco have introduced ‘Enhanced VXLAN’ – this augmentation to VXLAN removes the requirement to deploy IP multicast and can utilise the VSM (Virtual Supervisor Module) for handling the distribution of MAC addresses to each of the VEMs (Virtual Ethernet Modules). This post will delve into the specifics of enhanced VXLAN and explain how the various modes work. Read the rest of this entry »