ArubaOS and Controllers

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Frequent Contributor I
Posts: 98
Registered: ‎08-19-2008

DHCP lease times? Issue.

What do you guys use for DHCP lease times on your wireless networks (external DHCP server)?
We have an issue were our DHCP server (Cisco) reports subnets almost full, however, the Aruba Controller shows plenty IPs available. I think the issue might be related with devices getting on the network for a very short time, going off line, but the DHCP server still holds that lease. We have lease times set at 1hour for the wireless network.
Shorter lease times maybe? Or something from the Aruba side that can be done?

Thanks!
Marcelo Lew
Wireless Network Architect-Engineer
University of Denver
Guru Elite
Posts: 21,280
Registered: ‎03-29-2007

Correct

You are 100% percent right. The external DHCP server determines who gets what.

Just because clients are NOT on the Aruba controller occupying an ip address, does not mean the address is not in use. A client can roam away and roam back, or in the case of some client devices, ALWAYS request the last ip address that it used. Lease times are individual based on circumstance. If you feel you're running, out, shorten it, of course.

To take a look at the DHCP activity on your controller, turn on DHCP debugging like this post here: http://airheads.arubanetworks.com/vBulletin/showthread.php?t=2373


Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

Frequent Contributor I
Posts: 98
Registered: ‎08-19-2008

Re: DHCP lease times? Issue.

I see many other universities running 30m or even 15m lease times on wireless networks. I think we will try 30m.
Thanks,
Marcelo Lew
Wireless Network Architect-Engineer
University of Denver
Aruba Employee
Posts: 509
Registered: ‎07-03-2008

Re: DHCP lease times? Issue.

Just keep in mind, Microsoft Windows starts the DHCP renewal process at half the DHCP lease time. So, a 30 minute lease means renewal every 15 minutes. Not sure if Macs do that as well, you may want to check.
Guru Elite
Posts: 21,280
Registered: ‎03-29-2007

Yes...

That is part of the standard... http://tools.ietf.org/html/rfc2131

"In both RENEWING and REBINDING states, if the client receives no
response to its DHCPREQUEST message, the client SHOULD wait one-half
of the remaining time until T2 (in RENEWING state) and one-half of
the remaining lease time (in REBINDING state), down to a minimum of
60 seconds, before retransmitting the DHCPREQUEST message."


Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

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