maybe one of these monitoring network tools like nagios, cacti or zenoss
After trying a few products to monitor my servers I tried the following and got a version to evaluate. Install was straight foward and I just needed to configure the virtual switch in Promiscous mode. This product combines a traffic analyser and IDS system which has proven to be very usefull to analyse the issues that were causing me so many problems.
Another bonus was I could configure a number of 'slave' units which allowed me monitor multiple ESX servers from a single central unit. This was very usefull.
Here's another one that has similar capabilities; lightweight footprint, promiscuous sniffing of guest-VM traffic, distributed architecture, natural language search, breach detection, and deep forensics. http://www.PacketSled.com