DHCP Lease duration

[googlemad]

Just wondering what everyone has set their DHCP Lease duration to?

 

We have a ton of wireless (Windows) laptops and a ton of different SSIDs/scopes, some are set to 4 days, some are set to 12 hours, some set to 4 hours etc so I would like to make it a bit more standard across the board!

 

Ironically some of our community sites use pfSense firewalls as a DHCP server instead for clients and those look to have a default of just 2 hours!

[Patrick]

I just have it set to 1 day, don't have a ton of free addresses so it helps free things up a bit as visitors devices aren't needlessly using up an address. We don't have a guest network (small primary) and our range is given to us by our LA.

[localzuk]

Lease length should depend on how often devices change on that network - so, for a guest wireless network I would have it set to a few hours. But for a network for teacher laptops that are there all day every day, a day or more should be fine.

[FN-GM]

Agreed with @localzuk - Our guest WIFI is just a few hours. For more permanent fixtures such as desktop and laptops we have it set to 10 days. We have plenty of free IP so no need to have anything shorter.

[Boredguy]

our WiFi DHCP server is set to a maximum of 4 hours, bit as we have setup over 2000 IP's for it to assign out, its not a major issue.

[gmonks]

8 hours

[ADMaster]

As others have said, it depends on the purpose / type of device.

I have all of our internal devices set to 4 days. This usually means they keep the same IP week after week.

Same goes for named guests such as student byod I prefer their IP to stay someone constant in the case I need to look at logs.

Guest wifi is only a few hours to a day I’m not sure.

Then I have one SSID that is set to minutes. This is for enrolling chromebooks. I ran out of IPs one year enrolling devices so set it up this way.

[pete]

It depends how much of an audit trail I need.

 

Hardware the school owns is usually ~8days and/or reserved IP if I need "do X if the IP is in range Y" for something or other.

 

Kit on the Student BYOD network is ~30 days for sorting out idiocy reasons (there's ~1,000 potential IPs available to ~200-300 Y12/Y13, so it's unlikely to run out).

[psydii]

Short leases on oversubscribed subnets will give all sorts of weird reliability issues if devices are ever on the network for longer than the lease renewal period.

 

Also if you have thousands of clients and very short leases this can actually be a significant load on your DCHP server and impact other clients as they have to listen (and for some messages, respond) to the broadcasts involved in renewal.

 

Large subnets and longish leases seem to fit most use cases. Unless you have a compelling reason to have short/long leases, the defaults (usually 7/8d days?) should be fine.

[googlemad]

I've set up one of the smaller community sites to 4 hours now to see if anyone complains, as it was set to 4 days!

 

The scopes have enough capacity as such to cope, apart from one which only had 250 or so addresses available but we managed to change the range/subnet for that one so it now can dish out 500ish addresses. Mainly just my OCD kicking in I think! The trouble is I work in a hospital so you get a lot of the staff with their laptops roaming around to several different sites per day and getting a DHCP lease for each new SSID/scope they end up at!

[FN-GM]

Also if you have thousands of clients and very short leases this can actually be a significant load on your DCHP server and impact other clients as they have to listen (and for some messages, respond) to the broadcasts involved in renewal..

 

Just to add to this. By default Windows tries to renew a lease half way through the expiry time. So if someone sets the lease time to 2 hours the computers will be going through the whole DHCP process every 1 hour. This is in addition to the process being carried out again when the machines boot.