Hi Hi
IP addresses that are dynamically allocated by a DHCP server have leases. A DHCP Discover message from a DHCP client can carry an expected lease. When allocating network parameters, the DHCP server compares the expected lease with the specified lease in the address pool and allocates an IP address with the shorter of the two leases to the DHCP client. When the lease expires or the client goes offline, the DHCP server reclaims the IP address, which can then be allocated to other clients. This mechanism improves IP address utilization.
When the lease reaches 50% (T1) of its validity period, the DHCP client unicasts a DHCP Request message to the DHCP server to request lease renewal. If the DHCP client receives a DHCP ACK message, the IP address lease is successfully renewed (counted from 0). If the DHCP client receives a DHCP NAK message, the DHCP client must send a DHCP Discover message to apply for a new IP address.
If no response is received from the DHCP server when the lease reaches 87.5% (T2) of its validity period, the DHCP client broadcasts a DHCP Request message to request lease renewal. If the DHCP client receives a DHCP ACK message, the IP address lease is successfully renewed (counted from 0). If the DHCP client receives a DHCP NAK message, the DHCP client must send a DHCP Discover message to apply for a new IP address.
If no response is received when the lease expires, the DHCP client stops using the IP address and sends a DHCP Discover message to apply for a new IP address.
When a DHCP client no longer needs to use the allocated IP address and the lease has not expired, the DHCP client sends a DHCP Release message to the DHCP server to request IP address release. The DHCP server saves the configuration of this DHCP client and records the IP address in the allocated IP address list. The IP address can then be allocated to this DHCP client or other clients.
To request a configuration update, a DHCP client can send a DHCP Inform message to the DHCP server.
Source: https://support.huawei.com/enterprise/en/doc/EDOC1100038106?section=j025&topicName=dhcp-client-renewal-of-its-ip-address-lease
