What are the consequences of a low Acct-Interim-Interval?

[Alan DeKok]

On Oct 16, 2019, at 2:58 PM, Houman <houmie at gmail.com> wrote:
> 
> Maybe I'm overthinking it, but we have currently the interval set to 300
> seconds.
> What happens if I set this permanently to 15 seconds?

  Most NASes will ignore it.  From RFC 2869:

      The Value field contains the number of seconds between each
      interim update to be sent from the NAS for this session. The value
      MUST NOT be smaller than 60.  The value SHOULD NOT be smaller than
      600, and careful consideration should be given to its impact on
      network traffic.

  Most NASes will set 300s as the minimum.  There is very little benefit to setting it lower than that.

> Based on currently
> logged in users (around 700 users at a time), the database, as well as the
> freeradius process (CPU/Memory), will be a lot more utilised than before
> due to an increased number of updates.
> 
> post-auth {
>        update reply {
>                Acct-Interim-Interval = 15
>        }
> 
> Is there an industry standard value that is considered fair? Or can I go as
> low as 15 seconds without fearing scalability issues?

  Why would it be 15s?  There's no real benefit.

  Alan DeKok.