How does accounting-on/off work with RADIUS proxy?

In the following diagram, if one NAS, for example NAS-2, crashes and comes back, it will send system account-on message for RADIUS server to clean up previous sessions. But if a RADIUS proxy server is used in the middle, how can the true RADIUS server distingush the previous sessions on NAS-2 from

Re: How does accounting-on/off work with RADIUS proxy?

Zhiqiang Hu writes: In the following diagram, if one NAS, for example NAS-2, crashes and comes back, it will send system account-on message for RADIUS server to clean up previous sessions. But if a RADIUS proxy server is used in the middle, how can the true RADIUS server distingush the previous