This topic

Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

george_608 — Thu, 22 Oct 2026 19:41:26 GMT

Hub: BT Smart Hub 2, firmware v0.46.02.10311-BT (updated 17 Jan 2026), board R01, GUI 2.0.1 (30_06_2025)

Summary

Adding an address reservation ("Always use this IP address" = Yes) on a new device shows "Changes saved", but the reservation is never stored once the hub already holds 32 reservations. The Hub Manager page believes it has 128 slots, but the hub's configuration only has 32. Separately, a reservation for a device the hub lists as "Static" can't be switched off, so the table fills up with dead entries (mostly phones' private Wi-Fi addresses) and new reservations stop working with no error.

Steps to reproduce

Have 32 existing reservations (Advanced settings → My network; easy to reach because phones and laptops with private Wi-Fi addresses create new ones).
Open a device that isn't reserved, press Change settings, set "Always use this IP address" to Yes, press Save.
The page shows "Changes saved". Reload My network.

Expected: the reservation is kept, or the page says the reservation list is full.

Actual: the switch is back to No and no reservation exists. No error is shown.

What the page's own scripts show (my_network.htm)

dhcpReserveListNum is 128, but the config only has keys dhcpreserve1 … dhcpreserve32 (idxOfCfg("dhcpreserve33") returns -1).
When 32 are in use, the next free index handed to the device is 33, so setCfg("dhcpreserve33", …) is ignored and the request to apply.cgi still returns 200, which is why the page says "Changes saved".

Second problem: Static entries can't be removed

In the device view, AlwaysUseIP_O2F() returns straight away when Address assignment is "Static", so the switch can't be turned off and the reservation can't be deleted from the GUI.
Those dead entries keep using up the 32 slots.

Third problem: duplicate reservations

Two different devices were both reserved to the same address (192.168.1.115). The GUI allowed it without a conflict warning.

Workaround that worked: switch off reservations for non-Static stale devices (each freed slot then accepts one new reservation).

Suggested fixes

Make the GUI limit match the stored limit (or raise the stored limit to 128).
Show an error when the reservation list is full instead of "Changes saved".
Allow removing reservations for devices shown as Static.
Reject two reservations for the same IP address.

Re: Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

Crimliar — Thu, 22 Oct 2026 20:34:12 GMT

I can't help but feel the average BT home user has little need for such a large number of reserved addresses. My own network is probably just a little more complex than average, which is why I use a third party router. With a third party router, the devices that I need to access on the network all have their host names, and that's how I access them when I need to SSH or RDP into them. But I could if I needed to allocate every single of them an IP. So maybe it's time to either consider a third party router, or consider if you actually need to know the IP of each single device!

Re: Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

WSH — Thu, 22 Oct 2026 21:04:07 GMT

Reservations and static addresses are not the same thing. Reservations have always been a pain in the A, and not just on BT routers.

While reservations are “reserved” within the DHCP pool, static addresses are set on the device itself and nothing to do with DHCP. As such, they must be outside the range set by DHCP. On the SH2 that’s 1 to 63 by default.

You’d be far better using static addresses where possible.

Re: Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

george_608 — Thu, 22 Oct 2026 21:11:25 GMT

Yeah sure nice but that doesnt solve the underlying firmware bugs. I reported a bug is all

Re: Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

WSH — Thu, 22 Oct 2026 21:28:20 GMT

Oh the problem with the SH2 DHCP running out of address space has been being reported for years. If they haven't fixed it by now I doubt they will, especially as the SH2 is now obsolete.

And, like I said, reservations are notorious for being temperamental. One place I worked wouldn't allow the use of reservations at all, as they had caused problems in the past. Yet another place I worked used them all the time and never had any problems.

Re: Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

WSH — Thu, 22 Oct 2026 22:07:27 GMT

Just by coincidence, another thread on the same subject from a couple of days ago has just popped up. You might want to look at:

https://community.bt.com/t5/BT-Devices/DHCP-Reservation-bug-BT-Smart-Hub-2/m-p/2473681#M35107

Re: Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

Nick-P — Thu, 22 Oct 2026 22:14:16 GMT

Interesting post indeed. A bug BT must resolve, and likely directly ties into my own issue.

I agree the SH2 is obsolete by 2026 standards, however, wasn't the SH3 only just released to residential customers several months ago? 99.97% probably still have the SH2.

My firmware is:

Firmware version:v0.46.02.10311-BT

Firmware updated:Sun Dec 14 19:34:44 2025

Re: Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

george_608 — Thu, 22 Oct 2026 22:30:11 GMT

Yeah, i let Claude loose at my parents as theyve been having printer issues and i couldnt figure it out for the life of me.

Ended up being ran out of static addresses so every time printer goes to sleep had to add it as a new printer again.

they’re a perfectly normal long time bt customer who have been thinking their expensive printer is bad, purely because of BT!

Re: Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

Nick-P — Thu, 22 Oct 2026 22:36:56 GMT

If I'm in the right place, I think I just looked at the SH3. Is it really limited to 1Gb ethernet? Odd as OpenReach installed a 2.5Gb ONT a few years ago.

If I fire up an Opnsense/pfsense VM and pass through the entire PCIe card, I can connect straight from my rig into the ONT and it auto-negotiates a 2.5GBASE-T link.

Re: Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

Nick-P — Thu, 22 Oct 2026 22:35:51 GMT

Agentic? Or following instructions/chat?

Re: Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

george_608 — Thu, 22 Oct 2026 23:08:43 GMT

Fully agentic.

Re: Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

george_608 — Thu, 22 Oct 2026 23:09:06 GMT

Fully agentic

Re: Smart Hub 2: IP reservations silently fail after 32, and Static ones can't be removed

Nick-P — Thu, 22 Oct 2026 23:25:55 GMT

interesting but scary