DHCP lease expires question

[lamsf]

Hi,
I hv a question on DHCP lease expires.
I got this from a web site:

"After 50% of the lease time has passed, the client will attempt to renew the lease with the original DHCP server that it obtained the lease from using a DHCPREQUEST message."

If everytime at 50% of the lease time, the client wil attempt to renew the lease, when will the client actually stop having the IP, assuming that the client doesn't release the IP manually?

Or, another word, when will the lease actually expire since it will be renewed at 50% of the lease time? Assuming the DHCP server is working fine all the time.

Not sure if my question is valid, but I am just trying to understand...

Thanks.

 

[WhoKilledKenny]

If everytime at 50% of the lease time, the client wil attempt to renew the lease, when will the client actually stop having the IP, assuming that the client doesn't release the IP manually?

In a nutshell, 50% attempts with same DHCP server. If no answer, then at ~77% attempts to contact any DHCP (doesn't have to be the original DHCP server). At 100% if the client has not been able to reach a DHCP server, the lease expires.

Or, another word, when will the lease actually expire since it will be renewed at 50% of the lease time? Assuming the DHCP server is working fine all the time.

Say your lease is set for 8 days. On the 4th day the client successfully renews the lease. The lease expiration is re-set to 8 days. So assuming DHCP is working fine all the time, the lease continues to get reset to 8 days.

 

[lamsf]

Hi,
Thanks for your reply.

Can I ask more question?

Say your lease is set for 8 days. On the 4th day the client successfully renews the lease. The lease expiration is re-set to 8 days. So assuming DHCP is working fine all the time, the lease continues to get reset to 8 days.

So, as long as the DHCP server is working fine, the client will continue to hv the IP lease?

If I want the DHCP server to release the IP leased to the client after the client is idle for 30 minutes, how do I do that?

Thanks a lot.

 

[WhoKilledKenny]

If I want the DHCP server to release the IP leased to the client after the client is idle for 30 minutes, how do I do that?

I'm not sure what you mean by idle. A DHCP client will lose its lease when not online.
You can set lease times based on your needs. For example, I set up a DHCP scope for our Desktop team to do imaging and repair. Since they work on numerous machines a day, the lease time was set for 30 minutes. This way when they take the machine off the network, the IP is available again within 30 minutes.

 

[lamsf]

I am new to DHCP and may not hv enuf understanding of how DHCP works. I hv this question...

A DHCP client gets an IP from the DHCP server. The client does something, like web browsing, ftp, etc. After about half an hour, the client stops doing anything, i.e. not doing any web browsing, ftp, etc. It just sits there with its IP leased and still online (idle, such that it is not accessing the network, etc). Is it possible that the DHCP server take back the IP leased to the client after the client is 'idle' (like explained above) for, like, 30 minutes?

Thanks a lot.

 

[GunnarD]

No, DHCP server relase IP-adress when it expires.

 

[WhoKilledKenny]

Like GunnarD stated. The only time the IP becomes available is when the lease expires. The lease would only expire if communication was lost between the DHCP Server and the client. If you are experiencing some type of issue, I would suggest looking at the NIC Properties, Power Management, "Allow the computer to turn off this device to save power" check box. If enabled this could be causing an issue.