This is RFC 5997.  Freeradius supports status-server. See the configuration files for lots of documentation on it

> On Aug 10, 2015, at 11:39 AM, ICHIBA Sara <ichi.sara@gmail.com> wrote:
> 
> Hello there,
> 
> Is there anyone using LVS with Freeradius? In one of the previous threads
> (see below)  Alan said that we can use the status-server of freeradius in
> the MISC_CHECK. Unfortunately the link is no longer available. So If anyone
> has any information about this or tried this I would be very intersted to
> know how you did it.
> 
> In advance thank you for your response,
> Sara
> 
>>> Nicolas Baradakis wrote:
>>>> Keepalived will monitor the FreeRADIUS proxies. The health check is
>>>> configured with a "MISC_CHECK" stanza in keepalived.conf. You have
>>>> to run "radclient" and test whether the server returns Access-Accept,
>>>> that's all.
> 
>>> This is what Status-Server should be used for.
> 
>>> http://www.ietf.org/internet-drafts/draft-dekok-radius-status-server-00.txt
> <http://www.ietf.org/internet-drafts/draft-dekok-radius-status-server-00.txt>
> 
>>> I have an update I'll be submitting this week.  My goal is to have it
>>> issued as an RFC in the next 6 months.
> 
>>> Alan DeKok.
> -
> List info/subscribe/unsubscribe? See http://www.freeradius.org/list/users.html