I have run a report in Cisco Prime that shows the duration of the "last session". Based on this report I think our average is around three hours ...but it varies a lot. A /19 is pretty big. We have some /20's right now and I am thinking about possibly going bigger.
It seems the rule most admins are following is to find the average session time and make your DHCP lease twice that time. My thinking is a little different than that. I think you should provide the maximum lease time you can while keeping your scopes less than 50% depleted. My goals are: (1) To reduce unnecessary DHCPDISCOVER messages because the client can simply renew (especially when 90% are the same clients everyday), and (2) Reduce the likelihood of impact to clients from a DHCP failure by maximizing the amount of time between DHCPRENEWs for clients. In other words, if the entire DHCP service fails and my renew time is 12 hours away - the DHCP admins have a little more time to resolve things. Thoughts? Thanks, Curtis ________________________________________ From: The EDUCAUSE Wireless Issues Constituent Group Listserv <[email protected]> on behalf of Ian Lyons <[email protected]> Sent: Tuesday, May 8, 2018 6:52 AM To: [email protected] Subject: Re: [WIRELESS-LAN] DHCP Lease Times If you have Airwave one of the may "dials" is how long is your average connection. Mine is 28 minutes. I set my lease time for WiFi for 1 hour. I have a /19, which might be overkill, but with AD based DNS, I have poor insight into the things that go bump in the night (for DNS) If Cisco, I think there was a Prime option for this data too.... -----Original Message----- From: The EDUCAUSE Wireless Issues Constituent Group Listserv <[email protected]> On Behalf Of Curtis K. Larsen Sent: Monday, May 7, 2018 7:17 PM To: [email protected] Subject: [WIRELESS-LAN] DHCP Lease Times Hello, I'm curious to see what process/algorithm others use when determining DHCP lease times for your Wi-Fi networks. Assuming plenty of IP addresses, what DHCP lease time is ideal to assign to clients in a WLAN with 90,000 unique clients/day, where avg. user spends 3hrs connected , but some (maybe 20%) go several days, Keep in mind that 90% are the same user/device every day. What level of DHCP pool utilization do you think is best? Have you found any industry documentation on this? Thanks in advance. -Curtis ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss.
