[j] DHCP client sends a DHCPREQUEST packet 2J DHCP Serverl sends a DHC PACK packet
Purpose of the DHCP lease renewal process
ILLEGAL FOR NON-TRAINER USE
The DHCP lease renewal process is the process by which the DHCP client renews or updates its IP address configuration data with the DHCP server.
The DHCP client renews its IP configuration data prior to the expiration of the lease time. If the lease period expires and the DHCP client has not yet renewed its IP configuration data, then the DHCP client loses the IP configuration data and begins the DHCP lease generation process again.
The lease renewal process is the result of the lease period value. The lease period value ensures that DHCP maintains the IP address information and that clients regularly update or renew their IP address configuration data. Having DHCP maintain this information means that you can manage IP addressing from the DHCP server.
The client must renew its IP configuration data before the lease period expires. At specific intervals, a DHCP client attempts to renew its lease to ensure that it has up-to-date configuration information.
At any time during the lease period, the DHCP client can send a DHCPRELEASE packet to the DHCP server to release the IP address configuration data and to cancel any remaining lease.
A DHCP client automatically attempts to renew its lease as soon as 50 percent of the lease duration has expired. The DHCP client will also attempt to renew its IP address lease each time that the computer restarts. To attempt a lease renewal, the DHCP client sends a DHCPREQUEST packet directly to the DHCP server from which the client obtained the lease.
If the DHCP server is available, it renews the lease and sends the client a DHCPACK packet with the new lease duration and any updated configuration parameters. The client updates its configuration when it receives the acknowledgment. If the DHCP server is unavailable, the client continues to use its current configuration parameters.
If the DHCP client fails to renew its lease the first time, then the DHCP client broadcasts a DHCPDISCOVER packet to update its address lease when 87.5 percent of the current lease duration expires. At this stage, the DHCP client accepts a lease that any DHCP server has issued.
Note If a client requests an invalid or duplicate address for the network, a DHCP server can respond with a DHCP denial message (DHCPNAK packet). This forces the client to release its IP address and obtain a new, valid address.
If the DHCP client restarts on a network where no DHCP server responds to the DHCPREQUEST packet, the DHCP client will attempt to connect to the configured default gateway. If the attempt to connect to the default gateway fails, the client will cease using the leased address.
If a DHCP server responds with a DHCPOFFER packet to update the client's current lease, the client can renew its lease based on the server that offered the message and continue operation.
If the lease expires, the client must immediately discontinue its use of the current IP address. The DHCP client then begins the DHCP lease discovery process in an attempt to lease a new IP address. If the DHCP client fails to receive an address, the client will assign itself an address by using automatic IP address assignment in the 169.254.0.0 range.
Manual lease renewal You can renew an IP lease manually if you need to update DHCP configuration information immediately. (For example: if you want DHCP clients to obtain immediately the address of a newly installed router from a DHCP server, renew the lease from the client to update its information.)
Automatic lease renewal process
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