For Managed (No VLAN), Static, and System modes, you must
configure a Linux ethernet bridge on all NC machines. This
bridge connects your local ethernet adapter to the cluster
network. Under normal operation, NCs will attach virtual machine
instances to this bridge when the instances are booted.
To configure a bridge in CentOS 6 or RHEL6, you need to create a
file with bridge configuration (for example, ifcfg-brX) and
modify the file for the physical interface (for example,
ifcfg-ethX). The following steps describe how to set up a bridge
on both CentOS 6 and RHEL 6. We show examples for configuring
bridge devices that either obtain IP addresses using DHCP or
statically.