how to act in client when DHCP lease time is out by router?

[syjeon]

Hi 

I've configured DHCP pool on Cisco router. set the lease time 1 hours. I'm just wondering how to act in client side when 1 hr is gone after obtained the IP address?

the client need to renew the IP address every 1 hour when it needs to communicate? 

If the user download the application and it is over the 1 hours, then, the session will be disconnected and renew the IP address to start again?

[Francesco Molino · Accepted solution]

Hi

when your dhcp assign an IP to a device for 1h, the device uses it and at halfway of the time lease (30 minutes) it will ask the dhcp to extend the lease for 1h. Same every 30 minutes. 

If the device doesn't communicate and if the lease expires, then the dhcp server recycles this IP and it will assign this IP to another device. When the previous device is connecting back to the network, it will ask for a new IP. 

Until the device is connected to the network there is no impact for users (no disconnection). 

As the lease is very short, you need to be careful on how many requests will be sent to your dhcp server and it has to be able to handle all requests. 

Thanks

PS: Please don't forget to rate and mark as correct answer if this answered your question 

[syjeon]

Hi,

Thanks for quick answer.

So even though lease time is configured as 1 hr. the user is able to work such as file downloading which it may take 1 hr? because, the router is checking the every halfway. so, if the user is still using the IP address, then it will automatically extend the lease time? my understanding is correct?

[Francesco Molino]

Yes correct. Until it's using the IP, the lease is extended automatically and no interruption in a normal behaviour except if there are some issues (bugs, dhcp server not responding due to high process)

[pwwiddicombe]

DHCP will try "hard" to renew it's lease - starting at the 50% mark, and several times after that to renew.  I think at about 90% of it's lease, it will then attempt to get an address from *any* available DHCP server in the subnet; and once the lease has expired completely, it should revert back to 0.0.0.0 (or use the APIPA address 169.254.x.y), after which it will continue trying to get an IP from any DHCP server.