Originally Posted by fmalczewski
Thought about doing that, as I noticed that the attached devices are still renewing their leases every 1440 minutes and possibly going offline each time they renew it (I don't actually know if any of them actually go offline or not or if they are all well-behaved and renewal all happens transparently). At least their IP addresses are staying put.
Think I just need to be certain with the PC as her going offline briefly while working from home the other day was not good, so if it just happened to be DHCP related would want to eliminate that possibility altogether. A week or two lease should pretty well cover it though, since that PC isn't on for more than a day or two at a time.
They don't go off line when the lease is renewed. A lease is just a time for the DHCP server to check whether you're still alive. If you are, the lease is renewed and you keep the IP address. If the server decides you're not around anymore, it puts the address back in the pool to be reused when someone asks for an address.
If you renew the lease that happens in the background, is just paper pushing, has no impact on your IP address, etc.
If you shut down your computer, go away for a few weeks, etc. The lease time is exceeded and the IP address goes back into the address pool. The next time you connect, the DHCP server looks for an address for you. Earlier DHCP servers were pretty dumb about it and would give you whatever is available. Current DHCP servers will try to give you back the address you had before if it's still available.
Home networks have such a low number of clients, that it's almost (but not completely) guaranteed to get your old address back. So the lease / renew process is mostly transparent to the user. If you really want to be guaranteed an IP address, simply reserve one that you want within the router's address range and every time the router sees you, it will give you that address. Simple.
So no worries (usually) about the lease time. It is usually a good practice for a DHCP server to touch base every now and then to make sure all of its clients are really alive. If you have guests come over and they all hook onto your network with their iPhones, you may not want to have their leases hanging around for two weeks.