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Newbie
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Message 1 of 13

No IP addresses left. Allocated to ‘Disconnected’ devices.

While trying to use a new device I realised it wasn’t getting an IP address.  Though I have 100 addresses in the range and 40 active devices I noticed I had lots listed as disconnected, mostly old or devices that broadcast a random MAC address (iOS) so can lead to multiple entries.  Each of which still had an assigned IP address so not available in the range.  The lease is set to 1 day so I don’t understand why the disconnected devices aren’t getting dropped from the address table.  Even a reboot failed to release those addresses.  Can anyone assist since I’d rather not have to use another DHCP server?

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Distinguished Sage
Distinguished Sage
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Message 2 of 13

Re: No IP addresses left. Allocated to ‘Disconnected’ devices.

@D10nnis 

Welcome to this user forum.

The only way to clear out the address table on all of the home hubs, is by a factory reset.

http://bt.custhelp.com/app/answers/detail/a_id/11386/%7E/how-do-i-reset-my-bt-hub-to-its-factory-set...

IOS14 has made this problem a lot worse, especially for people who may have a wireless extender with a different SSID, as an additional set of random MAC addresses are generated for every IOS14 device.

 

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Newbie
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Message 3 of 13

Re: No IP addresses left. Allocated to ‘Disconnected’ devices.

Hi Keith,
Thanks for the prompt response.
It’s a shame that this is the only solution but thanks for letting me know. Now I know, I can keep an eye on the IP allocation and remove the disconnected devices manually again if needed. Yes, iOS14 is making things ‘interesting’, my iPhone had 8 entries in the address table!
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Distinguished Sage
Distinguished Sage
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Message 4 of 13

Re: No IP addresses left. Allocated to ‘Disconnected’ devices.

This issue started with the original Home Hub 1. I had one of the original ones which gave telnet access to the system and user configuration. It was clear then, that the entries were written to flash memory and there was no automatic script to remove them, but it could be done via a command line.

It would appear that much of the original core code (GPL) was kept in future home  hubs, as the problem persisted in the home hub 2,3 and 4 etc and it was not possible to  expire connections without deleting individual ones.

When I had the HH1, I used a separate DHCP server to overcome the issue.

I now use a TP Link router, which does not suffer from this problem.

I do not think BT considered it important, as if people had connection issues, then a factory reset cured the problem.

My daughter has a TP Link router in her house, and had multiple wireless hotspots, and all Apple devices, and there were at one point, 150 entries when the lease time was set to 48 hours.

Once the hotspots were replaced by a wireless mesh with a common SSID, only a single entry now exists  for each device. IOS14 must see it as a single seamless network, and does not generate a new MAC address, even though each node in the mesh, has a different BSSID. Interesting.

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Recognised Expert
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Message 5 of 13

Re: No IP addresses left. Allocated to ‘Disconnected’ devices.

@Keith_Beddoe @D10nnis 

The solution with iOS 14 is quite simple. Just change the default setting for the SSID in the iPhone/iPad to not generate a private MAC address.

Newbie
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Message 6 of 13

Re: No IP addresses left. Allocated to ‘Disconnected’ devices.

Thanks for the insight on their hardware.  It’s a shame BT didn’t think to resolve the potential issue. Obviously happy to receive additional support calls!

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Newbie
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Message 7 of 13

Re: No IP addresses left. Allocated to ‘Disconnected’ devices.

This wouldn’t solve the problem I highlighted just delay it. Without the automatic clearing of the address table, something every router I’ve previously owed has done the IP addresses available will still eventually run out. I’m not sure the customer should have to disable a function there to protect them to make up for a standard feature missing from the network equipment. 

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Recognised Expert
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Message 8 of 13

Re: No IP addresses left. Allocated to ‘Disconnected’ devices.

Don't totally blame BT for something that Apple are basically causing with this new "security" feature of private addressing that's on by default and very few people realise that it's there.

With this default setting everytime the iOS 14 device reconnects to the wifi a new IP address is assigned because the device has generated a new MAC address. Even my Asus has had loads of entries for my iPhone before I realised the issue. Over a day a single device could easily clock up 10 or more distinct IP addresses so imagine what a busy household could generate.

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Message 9 of 13

Re: No IP addresses left. Allocated to ‘Disconnected’ devices.

"A new MAC will be used whenever a new address has been generated and the device re-joins the network" (https://developer.apple.com/forums/thread/651151) hence with DHCP there is the potential for the one device to create not just one or two MAC and IP addresses on your hub but multiple entries.

 

 

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Distinguished Sage
Distinguished Sage
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Message 10 of 13

Re: No IP addresses left. Allocated to ‘Disconnected’ devices.


@V_Meldrew wrote:

"A new MAC will be used whenever a new address has been generated and the device re-joins the network" (https://developer.apple.com/forums/thread/651151) hence with DHCP there is the potential for the one device to create not just one or two MAC and IP addresses on your hub but multiple entries.

 

 


That would imply that whenever a DHCP lease expires, and the Apple device requests another, a new MAC address is generated.

In my daughter`s house, there are many Apple devices with IOS14. She is with BT FTTC using a TP Link router. Since her wireless is now being provided by a wireless mesh, only one MAC address is being generated.

The DHCP lease on the TP Link router is 48 hours, so the lease does not expire, as all devices are used every day, and each time a device accesses the router, the DHCP lease is reset to 48 hours again.

I mentioned this in an earlier post.

I remote monitor her router, and can view the DHCP table, and the system log, and can see each device sending a DHCP request.

 

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