DHCP - Address management during a disconnection

Question

When a host is disconnected, the assigned IP remains unavailable until the end of "lease time" or immediately becomes available to be reassigned?

How DCHP manages this?

Answer 1

If the client disconnect correctly through a DHCP Release (Graceful shutdown),

then the lease ends upon receipt at the DHCP server,

else the lease will expire upon the end of its actual "lease time".

This last case is the most frequent one (due to OS crashing, IP stack misbehaving and terminal leaving the scope of a wireless network).

Answer 2

During the DHCP BOUND state where the client has already obtained an IP address from the server, no further communication will occur between client and server until either...

• The client renewal timer triggers, and the client attempts to extend its lease (DHCPREQUEST during RENEWING state); or,
• The client releases its lease (DHCPRELEASE during BOUND state).

In both cases, the onus is on the client to initiate the action. The size of the pool of addresses in the DHCP scope, the lease duration, and the churn of clients must be considered so that all addresses are not exhausted. Reservations should also be considered because those addresses will never be available for the general subnet population.

In the event that the client is unable to reach the DHCP server to renew its lease, the client may end up obtaining a different lease from another DHCP server. The initial server that held the client lease will continue to do so until the lease expires.