[SOLVED] How to force ALL of the DHCP Clients to renew?

How to force ALL of the DHCP Clients to renew?

Is there any network broadcast call or something that can force all the connected DHCP clients to renew their addresses immediately?

And if not, why not? Surely this functionality has been desired by DHCP administrators from the date it was born. It makes changing a router address on a big network very hard without pervasive client automation.

Solution

It is not possible without letting the network down and up at the client network interface.

Theoretically, the DHCP server can send a FORCERENEW message to all connected clients. FORCERENEW is described at RFC3203. (See also https://serverfault.com/a/569869/107832)

Unfortunately, the famous ISC DHCP Server does not support it:

no current plans for RFC3203 support, also because of the lack of support for 3118 authentication
no real interested by users

RFC 3315 states in section 19.4.1 reconfigure messages. This is, however, for IPv6 only. A message states that DOCSIS 3.0 "requires Reconfigure support (for DHCPv6) as specified in RFC3315"