Security Onion (SO) is an amazing ubuntu-based network security monitoring (NSM) distribution. Security Onion can be deployed in a master-sensor distributed manner to allow for scaling.
Included in SO (Security Onion) is amazing set of features for managing network operations and network security tasks.
Learn more about Security Onion:
There is a great Intro to Security Onion on GitHub Wiki
Get right to the task of Downloading Security Onion and deploy it today (4 CPU, 8GB RAM)