Size RADIUS servers from authentication rate, interim accounting load and peak-to-average factor.
RADIUS load has two independent components: authentication, which spikes at shift changes and after an outage, and interim accounting, which is a steady drip proportional to concurrent sessions. Both hit the same server, so capacity is sized on their sum with a spare unit for redundancy. Wireless 802.1X re-authentication and roaming can push the peak factor above ten, and a RADIUS server that queues under a login storm locks every user off the network at once.
RADIUS Capacity
peak auth rate = users × auths per day ÷ 86400 × peak factor; interim accounting rate = concurrent sessions ÷ interim interval.
Combined server load
total tps = peak authentications + interim accounting records
peak auth rate = users × auths per day ÷ 86400 × peak factor; interim accounting rate = concurrent sessions ÷ interim interval. RADIUS load has two independent components: authentication, which spikes at shift changes and after an outage, and interim accounting, which is a steady drip proportional to concurrent sessions. Both hit the same server, so capacity is sized on their sum with a spare unit for redundancy.
Wireless 802.1X re-authentication and roaming can push the peak factor above ten, and a RADIUS server that queues under a login storm locks every user off the network at once.
This calculator takes 6 inputs: Users or devices, Authentications per user per day, Peak-to-average factor, Concurrent accounted sessions, Interim accounting interval, Capacity per server. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.