"release" Message from server side ?

[Meike Stone]

Hello,

I' a little bit desperated. In a NAC solution with captive portal for
wired clients, the client get the IP from a dedicated DHCP-Range
("public range"). The most of the user will keep this address, because
they only use Internet access.
But some users have a special account. At first, they get a IP-Address
from the "public Range" so they can login. But after login, they will
fall (the port who the client is connected) in a other VLAN with. This
VLAN has an other IP-Range.
Problem is, that I don't have a possibility (from view of server side)
to instruct the clients, to release and renew the IP.

At the moment this user have to restart their clients (or reconnect
the cable if possible).

An "automatic link down/up on the Switch is in this solution not
possible and will not work with all client OS.

Is there any other possibility to send a message, package or similar
from the server? It can be also bo done by an separate program, what
we have to write.

Thanks for help,

Meike