I like low lease times. DHCP server knows what's really on the network, and if something requests lots and lots of the pool you'll be fine in 15-30 minutes.
If things are set to a really long time, >=12 hours, you find out the next day when everything is broken (or you get alerts in the middle of the night). If you set them to a randomized 15-90m span, you get things breaking immediately when you screw up the dhcp server.
Hah. Your answer just has more questions. What on earth is requesting so many DHCP leases?
You've never accidentally spun something up that consumes all the leases?
It's just been a couple of times, but I've definitely done it (e.g. bridged a couple of networks that shouldn't have been).
But mostly, it's the other two things: it provides me with a list of hosts active now, and if the DHCP server is subtly broken I get a sentinel signal of something being wrong earlier (and it tends to be a partial instead of complete failure).
One more bonus: if I move something to a static lease, out of the pool, it'll renumber in a reasonable time and I don't need to go kick link state to get it to request again.
Things like really big caches and really long lease times: They're good for average performance, and they can let you ride out small problems. The flip side is that they tend to mask problems and to create really big demand transients at times. The trick is always to find a good middle ground.
Excellent answer - new appreciation for low lease times, thank you
Yeah, there's a lot of room to play between 900 and 86400 seconds.
Extremes of any sort generally aren't good. You fucked around and you found that out.
> You fucked around and you found that out.
I haven't had any notable issues with values in the 600-1200 second range, actually. (My macs don't wakeup to keepalive network on battery, though).
Modern devices will randomize MAC unless told not to when connecting / reconnecting to a wifi/Ethernet network.
When on a pretty standard /24 network subnet, if there are more than a few dozen devices coming and going, the lease table can fill up until older lease reservations expire.