I'm contemplating- when is a DHCP lease time too short for a very busy WLAN?
We have pockets where, say 2000 busy WLAN users may be on like 60 APs in a given building, largely still and non-roaming, with 1 hour DHCP leases. If we shrank the lease time to 30 minutes, so that every 15 minutes we have DHCP renewals in the air (we don't use DHCP proxy on the controller- bit too many times by past bugs)- could that amount to a volume of low-value traffic in the air that could become problematic? What about lease times of 15 minutes? When does short = too short because of added overhead in the cells, APs, or controllers (3500s, 3600s, 5508s)? Is it ever of concern (beyond the servers ability to keep up)- especially given that the entire network that would feel the effect of shorter lease times itself has 15K clients on it.
Before we try to do any structured analysis, just wondering if anyone has gone down the road of ever shrinking lease times (on an 802.1x WPA2 network) and came to regret it for any reason in a Cisco WLC environment?
My opinion is this: The BIGGER the subnet, the SHORTER the lease time.
This holds true when you have a Guest DHCP scope. You don't want a 1 hour guest getting their IP address reserved for more than 4 hours. So ideally, you can get away with setting the Guest SSID's lease time down to 30 minutes.
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