Duplicating accounting data between servers

[Chris Adams]

I am setting up a couple of servers FreeRADIUS 3.0.4 (CentOS 7).  They
are pretty basic, handling RADIUS for dialup users.  The users are
stored in SQL (each servers has a local MariaDB instance, provisioned by
an external management system).

I have accounting data going to SQL as well, but then each server just
has its own records (and of course NASes tend to flip back and forth on
their own), so I would like to have FreeRADIUS duplicate the accounting
records to both servers (so server A sends what it gets to server B and
vice versa).

I see radrelay references in buffered-sql and the like, but what I don't
see is how do I keep accounting records from looping?  If both servers
are configured to copy to the other, what keeps records from bouncing
back and forth?  Or will they only forward records they receive directly
from NASes?  I couldn't find anything that explicitly documents that
behavior.

-- 
Chris Adams <cma at cmadams.net>