DHCP server settings

[Atkins, Dwane P]

We recently lowered our DHCP lease time to the default of 2 hours.

After a couple hours, I was checking the DHCP leases and see some that have a difference of 2 hours from the Start and End time. However, there are some that have a 24 hour difference. Is there a way to completely clear out the DHCP lease time and restart the DHCP server. These leases started almost 3 hours after I had modified the default lease time.

Thanks

Dwane

[Atkins, Dwane P]

I am not trying to spam mail, but should we set the maximum lease time as well? It is currently at default.

Dwane

From: Atkins, Dwane P [mailto:ATKINSD-***@public.gmane.org]
Sent: Tuesday, March 15, 2011 10:34 AM
To: 'support-***@public.gmane.org'
Subject: [pfSense Support] DHCP server settings

We recently lowered our DHCP lease time to the default of 2 hours.

After a couple hours, I was checking the DHCP leases and see some that have a difference of 2 hours from the Start and End time. However, there are some that have a 24 hour difference. Is there a way to completely clear out the DHCP lease time and restart the DHCP server. These leases started almost 3 hours after I had modified the default lease time.

Thanks

Dwane

[Adam Thompson]

Yes. Many clients will automatically ask for longer lease times than your default.

-Adam





From: Atkins, Dwane P [mailto:ATKINSD-***@public.gmane.org]
Sent: Tuesday, March 15, 2011 10:36
To: 'support-***@public.gmane.org'
Subject: [pfSense Support] RE: DHCP server settings



I am not trying to spam mail, but should we set the maximum lease time as well? It is currently at default.



Dwane



From: Atkins, Dwane P [mailto:ATKINSD-***@public.gmane.org]
Sent: Tuesday, March 15, 2011 10:34 AM
To: 'support-***@public.gmane.org'
Subject: [pfSense Support] DHCP server settings



We recently lowered our DHCP lease time to the default of 2 hours.



After a couple hours, I was checking the DHCP leases and see some that have a difference of 2 hours from the Start and End time. However, there are some that have a 24 hour difference. Is there a way to completely clear out the DHCP lease time and restart the DHCP server. These leases started almost 3 hours after I had modified the default lease time.



Thanks


Dwane

[Atkins, Dwane P]

Thank you, Adam. We had the DHCP default lease time set to 4 hours and the Maximum lease time was set to the default of 24 hours. So we lowered the default lease to 2 hours and left the maximum lease at 24 hours. What this tells me is that with the default lease, it will do another DHCP negotiation at the œ life or in this case an hour. The maximum lease time says that 10.10.10.10 will only be allowed to lay claim to that lease for one day. Is this a correct assumption? Should I lower the maximum lease time as well?

Thanks

Dwane

From: Adam Thompson [mailto:***@athompso.net]
Sent: Tuesday, March 15, 2011 12:05 PM
To: ***@pfsense.com
Subject: RE: [pfSense Support] RE: DHCP server settings

Yes. Many clients will automatically ask for longer lease times than your default.
-Adam


From: Atkins, Dwane P [mailto:***@uthscsa.edu]
Sent: Tuesday, March 15, 2011 10:36
To: '***@pfsense.com'
Subject: [pfSense Support] RE: DHCP server settings

I am not trying to spam mail, but should we set the maximum lease time as well? It is currently at default.

Dwane

From: Atkins, Dwane P [mailto:***@uthscsa.edu]
Sent: Tuesday, March 15, 2011 10:34 AM
To: '***@pfsense.com'
Subject: [pfSense Support] DHCP server settings

We recently lowered our DHCP lease time to the default of 2 hours.

After a couple hours, I was checking the DHCP leases and see some that have a difference of 2 hours from the Start and End time. However, there are some that have a 24 hour difference. Is there a way to completely clear out the DHCP lease time and restart the DHCP server. These leases started almost 3 hours after I had modified the default lease time.

Thanks

Dwane

[Chris Buechler]

Thank you, Adam.  We had the DHCP default lease time set to 4 hours and the
Maximum lease time was set to the default of 24 hours.  So we lowered the
default lease to 2 hours and left the maximum lease at 24 hours.  What this
tells me is that with the default lease, it will do another DHCP negotiation
at the ½ life or in this case an hour.  The maximum lease time says that
10.10.10.10 will only be allowed to lay claim to that lease for one day.  Is
this a correct assumption?  Should I lower the maximum lease time as well?

Generally, unless you have an unusual circumstance, you'll want the
maximum lease time to be closer to your default lease time as you
typically don't want clients to get a much longer lease than your
default.

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[Adam Thompson]

If you had your DHCP lease times set to 24hrs, lowering them will take a minimum of 12hrs (0.5 * least time) to take effect, and many DHCP clients are slightly broken and will take a full (lease time) to renew. Not to mention any of the really broken clients who don’t honour changes to the DHCP lease as long as they keep getting DHCPACKs – it sounds like this might be what you’re experiencing. The only solution is – usually – to reboot the device. If you have Win95/98 clients, you may have to use regedit to make it forget its old lease.

-Adam Thompson

athompso-gKoiEJA+***@public.gmane.org





From: Atkins, Dwane P [mailto:ATKINSD-***@public.gmane.org]
Sent: Tuesday, March 15, 2011 10:34
To: 'support-***@public.gmane.org'
Subject: [pfSense Support] DHCP server settings



We recently lowered our DHCP lease time to the default of 2 hours.



After a couple hours, I was checking the DHCP leases and see some that have a difference of 2 hours from the Start and End time. However, there are some that have a 24 hour difference. Is there a way to completely clear out the DHCP lease time and restart the DHCP server. These leases started almost 3 hours after I had modified the default lease time.



Thanks


Dwane