[CentOS] USB Serial Ports

We have several CentOS 6 systems that are used in various configurations
of test equipment.  One of the primary functions of these systems is the
connectivity to serial ports of some operational systems that have serial
port control requirements.  Lack of interface bus slots led us to the use
of USB connected serial ports on these CentOS 6 systems.

We first used these USB connected serial ports in our RHEL 5 test equipment
systems.  With RHEL 5, shut down and boot up of the systems would often
cause the serial ports to have a different driver name, even though we had
not changed the ports where the USB devices were plugged in.  This caused
software access problems until we discovered what could be done using the
udev rules to lock in the driver names.

This problem seems to have gone away in our newer systems with CentOS 6,
and we would like to make sure that it does not return.  We are deploying
some of the systems and do not want to have software access issues in the
field where fixes are more difficult.  We would like to know if there is
some underlying factor that has solved this problem for us.  Any ideas on
what to check would be greatly appreciated.