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Unable to assign static IP to devices

evansnp — Sat, 18 Nov 2023 11:39:45 GMT

A couple of days ago a friend called me to say that one of his network devices appeared several times in the address table, and he was unable to assign it a static IP address. Yesterday, exactly the same thing happened to me. A device which has had a statically assigned DHCP IP address for years disappeared off my network (I thought), but appeared with a different IP address. Looking at the router, there were 4 entries for the same device, each with a different IP address, but the same MAC address (how is that possible?). I tried to remove the spurious entries, and rebooted the router. The rouge device now only appears once, with the wrong IP address. I have tried numerous times to set this to be static, to no avail. The router says that the changes need to be saved, which I do, but it remains as dynamic. I know that in the past the DHCP server in the router has been flaky, but not it's unusable. I'm assuming that the recent FW upgrade has turned something that was really bad, into something that is unusable.

PS: Until I was forced to move to DV I used my own router, which was brilliant (Mikrotik). I am seriously thinking of ditching DV so that I can use a router that actually works as advertised!

Re: Unable to assign static IP to devices

countrypaul — Sat, 18 Nov 2023 12:29:15 GMT

A static IP address is set on the device and not be DHCP from a server (routers often act as DHCP servers).

A Reserved address can be set on a DHCP server so that a given MAC address is normally assigned the same IP address. If the DHCP server runs out of IP addresses other than unused Reserved ones it may issue those to other devices.

If you have certain devices such as recent Apple iPhones/iPads (but not only Apple devices) they default to randomised MAC addresses which can result in DHCP servers running out of free IP addresses to issue as they can end up using multiple MAC addresses and therefore being issued with multiple IP addresses.

I don't know what other devices are on your network so can't know whether this can be influencing your problem.

Re: Unable to assign static IP to devices

Anonymous — Sat, 18 Nov 2023 12:34:11 GMT

@countrypaulwrote:
I don't know what other devices are on your network so can't know whether this can be influencing your problem.

Even Windows 11 is in on the act now.

Re: Unable to assign static IP to devices

evansnp — Sat, 18 Nov 2023 17:27:35 GMT

I think that you are all missing the point. I am assigning IP addresses, via DHCP, based on MAC addresses, so the DHCP server should assign the same address always (i.e.. a 'static' address). The BT router will not let me set 'always use this address'. Or, more accurately, it lets me change it, and save it, but does nothing. This has been a bug in the router software for as far back as I can remember.

Re: Unable to assign static IP to devices

licquorice — Sat, 18 Nov 2023 17:55:18 GMT

For the pedants amongst us, it's not a static address, it is a reserved address. A static address is permanently fixed on the device itself.

A static address assigned by DHCP is an oxymoron.

Re: Unable to assign static IP to devices

evansnp — Sat, 18 Nov 2023 18:07:15 GMT

And in reply to the main question?

Re: Unable to assign static IP to devices

licquorice — Sat, 18 Nov 2023 18:11:58 GMT

The SH2 is hopeless.

Try a factory reset and start again, as much as a pain as that might be.

Or give your devices true static addresses.

Re: Unable to assign static IP to devices

countrypaul — Sat, 18 Nov 2023 18:39:34 GMT

If the problem is as you say a bug in the SH2 software then why not use a different DHCP server and turn DHCP off on the SH2? Using something like Pi-Hole would allow you more control including setting your own choice of DNS servers (another source of frequent frustration).

Re: Unable to assign static IP to devices

evansnp — Sat, 18 Nov 2023 18:49:01 GMT

@countrypaul that’s a really good call! I have a few devices that I could run a DHCP server on. If the SH 2 worked as it was intended to, I wouldn’t need to do it though!

Re: Unable to assign static IP to devices

evansnp — Sun, 19 Nov 2023 11:38:34 GMT

I've moved DHCP provision over to one of my Synology Nas servers, and all working fine, but logging on the Synology DHCP is a bit limited. In the longer term I'll re-introduce my Mikrotik router back into the network.

Re: Unable to assign static IP to devices

countrypaul — Sun, 19 Nov 2023 11:46:55 GMT

@evansnp If the SH2 worked as who intended? We all think we know what it should do, but it could well be that someone in the BT team has other ideas for reasons unknown to the rest of the world!

At least you have a working solution, you could always introduce your own router just acting as a switch, DHCP server, and WAP leaving the SH2 for simple routing and DV.

Re: Unable to assign static IP to devices

evansnp — Sun, 19 Nov 2023 12:09:18 GMT

I have been thinking about going back to the Mikrotik for a while, perhaps I’ll do what you suggest I.e. just use the Mikrotik as a switch, and providing DHCP, DNS etc. I’d like to use it for the firewall too, but then it would need to be in router mode, which means double NATing ….. Yuk!

Re: Unable to assign static IP to devices

countrypaul — Sun, 19 Nov 2023 12:24:16 GMT

I have never played with a Mikrotik but thought you could use it as a firewall in bridge mode rather than router mode. I may be completely wrong by the way because as I said I have never had a chance to play with one.