DHCP Lease Time on BT Home Hub 2?

For the past few months I have been having apparently random wi-fi disconnects on various devices often at very inconvenient times when in the middle of streaming some live sport. So ahead of this upcoming heavy weekend of sport I logged into the Home Hub to give it a reboot in the hope that it would remain stable for the next few days.

But, browsing through the various settings (as you do) I came across the DHCP Lease Time and saw that it was set to 24 hours for each device. Curious!! So I changed them all to 21 days then went ahead with the reboot then checked that all devices had their lease time updated. I also put a three-weekly reminder in my phone diary to reboot the router on the Tuesday (after that weekend's sport).

I am assuming that BT forced an update those months ago that had the effect of changing the lease times? Or has it always been set to that but for some reason never been such an issue before? Or was it the reason for the dis-connects at all? Is it less secure to have such long lease times and I would be adviced to change back to shorter times?

24 hours is the recommended lease time for DHCP servers, especially for home use. If this is causing clients to lose their leases then you have some other problem. A device that is on when the lease expires will renew it automatically (with the same address). It shouldn't matter if a device loses its lease when it is switched off (assuming you don't want it to have a fixed IP address) as it will just acquire a new lease when it is next switched on. If you want it to retain its IP address you should switch on the "Always use this IP address" in its settings via the address table.

I can't say for sure but I would be very surprised if the default was ever different from the recommended 24 hours.

Setting a longer lease time isn't a security risk but does mean that there is a greater chance of running out of available addresses. Probably not a problem as you have 253 to play with, so if 21 days works for you that's no problem. I'm not sure what rebooting the router every 21 days would achieve; it won't affect the DHCP assignments as these should persist across a reboot.

DHCP doesn't wait until the lease expires before it renews - it sends out a request to renew when it hits 50% of the lease time. With a 24 hours lease this would give 12 hours for the device to renew the lease before the lease expires.

As you say changing the DHCP lease time is unlikely to make any difference and is likely a red herring to the actual problem the OP has.

In reply to a post by ian72:

DHCP doesn't wait until the lease expires before it renews - it sends out a request to renew when it hits 50% of the lease time.

That's true, I wonder if I have a problem.

Text
1 2	Lease Obtained. . . . . . . . . . : 25 February 2024 13:53:34 Lease Expires . . . . . . . . . . : 09 March 2024 07:59:23

That depends upon how the server is configured. 50% is the default before the RENEWING state is entered, but can be altered (I suspect that for the BT hub it is fixed at 50%). The RFC only says that this time must be earlier than the REBINDING time (which defaults to 87.5% of the lease time) which, in turn, must be earlier than the lease expiration time. But the lease remains valid until the lease expiration time if there is no response to DHCPREQUEST messages.

I'm not sure that this level of detail is really relevant to an outline understanding of the workings of DHCP.

Do you have the Wifi channels set to Auto? Sometimes if the channel selection is set to Auto, the Wifi can move channels and cause disconnects whilst doing so.
It may be worthwhile checking, and using a cabled connection if at all possible. Personally I only use Wifi when there is no other option.

In reply to a post by gomezz:

For the past few months I have been having apparently random wi-fi disconnects on various devices often at very inconvenient times when in the middle of streaming some live sport.

How do you know this is a "wi-fi disconnect"?

If you are on an FTTC line, and the line quality deteriorates and forces a retrain, this could cause a few seconds of interruption to service and/or a change in your dynamic IP address.

You may be able to look in your router logs to see if there is evidence of such activity (I don't know what level of logs the HH2 provides though).

Depending on how it is reporting I am not sure why that would be a problem. The original lease was obtained on 25 Feb, it has quite possibly renewed every day or more since and the next expiry is 9 March. I would check maybe tomorrow morning and see if the expiry has changed but the lease obtained is the same - I suspect that will be the case and just means it keeps extending the lease but the lease obtained date doesn't change.

In reply to a post by ian72:

I would check maybe tomorrow morning and see if the expiry has changed but the lease obtained is the same - I suspect that will be the case and just means it keeps extending the lease but the lease obtained date doesn't change.

I would have expected the "lease obtained" date to reflect the latest renewal, which is more interesting information than whatever date the lease was initially obtained.

I presume Windows logs lease renewals in the event log, somewhere.

I can't find a definitive answer but based on the evidence in your post I believe "Lease obtained" is when the IP address was first assigned to the device within the session. This will not change for a lease extension. I can think of times it is much more useful to know when the IP was assigned to the device rather than the last time it was extended.

As I said check a little before it is due to expire to see if the expiry has changed and see if the lease obtained changed - I suspect the former will but the latter won't.