When designing a solution which does replication one of the questions are: how much bandwidth does the replication traffic uses?
VMware has a solution called vSphere Replication which is able to replicate selected virtual machines for disaster recovery purposes.
To model the impact on the network VMware recently released a new tool named vSphere Replication Capacity Planning Appliance. This free tool available as a fling (unsupported technology preview software) can be used without producing actual replication traffic.
The appliance provides command-line tools to configure replication for any VM in a vSphere Virtual Center. The replication is established in preview mode and thus requires no storage space. Networking traffic, required for the replication, is measured and displayed in an easy-to-understand graphical format that allows you to estimate the network bandwidth required. Graphics representing network traffic can be seen when connecting to the ip address of the appliance.
Download and instructions here.