This topic

BT SmartHub 2 keeps changing DMZ device IP

alman — Sat, 09 Dec 2023 12:37:43 GMT

I have a device that needs to be outside the DMZ,

However if I set the IP or Machine name in the DMZ , within an hours it changes to another IP address.

It sometimes chooses randomly a device that MUST not be outside on the DMZ.

I've tried it with the DHCP is disabled and enabled on the BT HomeHub.

But the result is the same.

The posts below explain the same problem but there is no solution

Solved: BT Business hub 2 - DMZ ip changing itself - BT Community

BT hub randomly reassigns DMZ - BT Community

Re: BT SmartHub 2 keeps changing DMZ device IP

Keith_Beddoe — Sat, 09 Dec 2023 12:41:00 GMT

@alman

Welcome to this user forum for BT Retail phone and broadband customers.

Are you a business user?

Re: BT SmartHub 2 keeps changing DMZ device IP

WSH — Sat, 09 Dec 2023 13:00:01 GMT

Yes, I’d agree.

The only thing mine connects to is a second router, (a Draytek), set up as DMZ host but I have noticed that if I plug a laptop into the SH2 to directly configure it, it loves to switch to the laptop when it reboots. This isn’t a problem when the laptop is disconnected, of course as that IP no longer exists and I’ve got used to checking it is on the correct IP for the Draytek before I leave it any way, but it is strange.

Be interesting to see if anyone has a solution/explanation.

Re: BT SmartHub 2 keeps changing DMZ device IP

alman — Sat, 09 Dec 2023 13:15:02 GMT

Not business user, I have a normal Halo 900 fibre account.

The device in the DMZ never reboots, remains on 24hours a day

Yes the SmartHub2 changes the IP address, like someone logged and changed it.

Nothing reboots, everything is left on, yet the configured IP in the DMZ changes.2

Re: BT SmartHub 2 keeps changing DMZ device IP

licquorice — Sat, 09 Dec 2023 15:50:22 GMT

Is the IP you are allocating outside of the DHCP range of the hub, regardless of whether DHCP is enabled or not?

Re: BT SmartHub 2 keeps changing DMZ device IP

alman — Sat, 09 Dec 2023 16:36:28 GMT

yes, the IP is within the range, although DHCP is off.

so I've enable the DHCP, although not authorititative , and set the range at the top end out of the way.

....shall see if that helps, and will report back

Re: BT SmartHub 2 keeps changing DMZ device IP

licquorice — Sat, 09 Dec 2023 17:31:18 GMT

It needs to be outside of the DHCP range, NOT within it.

Leave the range as default.

Re: BT SmartHub 2 keeps changing DMZ device IP

WSH — Sat, 09 Dec 2023 17:45:05 GMT

Ah, the flakey SH2 DHCP again. I must admit that I'd assume it would make no difference if it was disabled.

Re: BT SmartHub 2 keeps changing DMZ device IP

alman — Mon, 11 Dec 2023 16:17:16 GMT

( since first posting I've been hit with the worst flu )

So I've tried a limited top end DHCP range, and that didnt work.

So will try default DHCP range and pushing this devices IP to somewhere below 40.

The thing is , this device is a stubborn thing and has no IP config, so am using PiHole DHCP to assign to less than 50

Re: BT SmartHub 2 keeps changing DMZ device IP

licquorice — Mon, 11 Dec 2023 16:39:36 GMT

Hang on, so the device you are putting in the DMZ doesn't have a static IP address?

Re: BT SmartHub 2 keeps changing DMZ device IP

WSH — Mon, 11 Dec 2023 16:57:46 GMT

@licquorice Funnily enough, that's what I thought but I decided to wait and see what was said next.

Re: BT SmartHub 2 keeps changing DMZ device IP

alman — Mon, 11 Dec 2023 17:26:32 GMT

The device had its static assigned by the BT router,

But as the behaviour of that BT router was ..... challenging,

I started trying to move components away from the BT Router :

Setting up DNS and DHCP on another box, then tried a PiHole so assigned a static AND a DNS to it.

But.... still the BT box randomly applies different IP addresses to the DMZ, despite the device having the same....and never ever changing.

Sometimes it would give the correct device name, but some random ip, which is why I tried the DNS.

I've tried turning the DHCP back on with a range above 200,

the device still holds its low number ip, yet the DMZ assigned is random

Re: BT SmartHub 2 keeps changing DMZ device IP

licquorice — Mon, 11 Dec 2023 17:33:26 GMT

You can't assign a static address with a router, that is an oxymoron.

You need to give the device a true static address on the device itself.

Re: BT SmartHub 2 keeps changing DMZ device IP

WSH — Mon, 11 Dec 2023 17:57:54 GMT

Yes, static addresses by definition are NOT assigned by DHCP. They are assigned by the administrator, manually on the device itself. The only reference to DHCP is that they must be outside of the range being assigned by DHCP or DCHP will sooner or later issue the same address to another device, causing a conflict.

You may be confusing it with “reserved addresses” where they are assigned by DHCP but the same address is always assigned to the same MAC address. The DMZ set up will be a lot easier with a proper static address.

Re: BT SmartHub 2 keeps changing DMZ device IP

alman — Mon, 11 Dec 2023 17:59:56 GMT

I meant Static DHCP lease, rather than static IP.

Re: BT SmartHub 2 keeps changing DMZ device IP

WSH — Mon, 11 Dec 2023 18:05:43 GMT

Well again, that is contradictory. You can’t have a static lease. By definition a ‘lease’ is not permanent.

Re: BT SmartHub 2 keeps changing DMZ device IP

alman — Mon, 11 Dec 2023 18:53:17 GMT

here’s how to setup static lease,

https://discourse.pi-hole.net/t/setting-up-dhcp-leases-for-static-ips/21514

Either way, I’ve now removed PiHole from the mix.

Ive set the devices up manually ( which has held through no problem there)

ive turned the dhcp of the bt router on with a high range , and disabled it.

same result , after an hour or so the DMZ ip is reset randomly.

Re: BT SmartHub 2 keeps changing DMZ device IP

WSH — Mon, 11 Dec 2023 19:10:52 GMT

I can see where you're getting the confusion from.

As I said before, a reserved address is not the same thing as a static address. Reserved addresses can be flakey. One place I worked wouldn't allow them for that reason. (Then again, another place I worked did everything as reservations without any apparent problems). I still stand by the comment that a proper static address will be more reliable.

Re: BT SmartHub 2 keeps changing DMZ device IP

WSH — Mon, 11 Dec 2023 19:38:55 GMT

As far as “static leases” go, what really happens is that the device will request a lease renewal before it expires and so a continually running device will appear to have a ‘permanent’ lease. In fact, it is getting a new lease every few days.

In the case of a reservation, even if the lease expires, (because, say, the device was turned off), the device requests a new address and the address that it gets is the same one, with a new lease. That’s the idea of a reservation.

Incidentally, just to clarify a reserved address must be within the DCHP scope. A static one is outside of that scope.

Re: BT SmartHub 2 keeps changing DMZ device IP

alman — Thu, 14 Dec 2023 18:36:08 GMT

the ip on the device is static and configured within it.

the ip in the bt router for setting outside the DMZ changes in less than an hour to random numbers outside of the range set in the dhcp.

I’ve tried dhcp on and off with a small high range including the static ip and without.

the solution I’ve come up with is to turn the firewall off and to put another router on the inside , with the firewall turned on, where all my networking is attached to.

its a better router anyway than the bt one , I have more control. FritzBox that I had lying around