Why Nexus 1000v

Why N1kV :- With an ESX host and it's DVS allowing VMNICs on individual VMs to communicate with internal and external networks, we had following issues :-

A. Using single port or a port channel from DVS to upstream switch:-

1. VMs creating bridges and unintended loops.
2. Unintended VM to VM communication.
3. Even though VMNICs could be on separate internal networks, the uplink is common through the DVS and hence the all VM traffic would traverse through the upstream switch regardless of the requirement. 
4. VMs on wrong VLANs leading to no external/upstream connectivity.

B. Using Multiple ports with separate VLANs allowed on upstream switch per port on ESX host. 

1. This required high number of physical ports on the switches as well as each hosts (multiple NICs, multi-port NICs)
2. The n/w admin still had very little control over the DVS config and the VLANs on each of the VMNICs.