run script on dhcp events

[Семёнов Евгений Владимирович]

Sorry, my question was too unclear, I will explain.

I develop new university WiFi captive portal and use freeradius as 
authentication/accounting and dhcp server. I call script from 
DHCP-Request section to set firewall rule (because i need supplicant 
MAC-address and issued IP-address). And i need to know where i can call 
script to remove firewall rule after supplicant disconnected from WiFi 
network.

I tried to call a script (that remove firewall rule) from accounting 
section when Acct-Status-Type equal Stop, but it is work only for 
standalone wifi access point without neighbors with same SSID. But when 
the supplicant passes through the Wi-Fi zone and communicates with one 
access point, and then with another, the scheme described above stops 
working, because after receiving the acct-stop packet from the first 
access point, the firewall rule is deleted, but does not create a new 
one (there may not be a new dhcp-request).I want to try to call script 
that deletes a firewall rule after releasing the IP address of the 
supplicant or after dhcp decides that the supplicant has not confirmed 
the address and marks the address as unoccupied. But i don't know where 
i can do it.

Maybe you will advise me something?

-- 
Evgeniy