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From the author of VXLAN Unicast Mode

VXLAN Unicast Mode

The most recent version of Nexus 1000V for VMware vSphere brought an interesting variation of VXLAN to facilitate the adoption of this protocol in server virtualization clusters. Avoiding the multicast requirements from the original IETF draft, Nexus 1000V raises the possibility of IP unicast traffic between VEMs that share the same VXLAN segment.

In this model, a VEM doesn't have to learn MAC addresses from remote VMs through flooding. In fact, the active VSM automatically publishes this information to all VEMs that share that VXLAN segment. As a result, whenever traffic must be sent to a remote VM, each VEM will simply encapsulate the original frame into a VXLAN packet destined for an already known unicast IP address. As for multidestination traffic such as broadcast, the VEM will provide local replication to other VEMs with the same VXLAN segment.

Nexus 1000V now also supports the integration of a VXLAN Gateway, which can "weld" a VLAN and a VXLAN in a 1:1 association. In summary, the gateway permits Layer 2 connectivity between physical resources and VMs connected to a VXLAN segment. However, note that designs joining VLANs to VXLAN in highly scalable environments might undermine the scalability and independence VXLAN segments normally provide.

The VXLAN gateway is deployed as a virtual blade in the Nexus 1110 appliance and logically works as an additional module on a Nexus 1000V instance.

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