Iphones taking incorrect Ip address

[Steve252]

Hi,

I have several devices connected  to my smart modem, laptops, tv's, console and android phones, I've been on full fibre since last July.  Lease time on the ip addresses is set to 21 days, all works well and all stay on the same ip address which is important as some of the devices linked together and must have a stable IP address.

When the grandkids turn up and they go on the wifi, they will always take an ip address that was previously allocated to another device even though that device gets the ip address by dhcp and they are always online within the 21 days of the lease so it gets refreshed. 

Anybody else having same/similar issue with iphones on the internal wifi, this only happens with iphones.

regards

[Keith_Beddoe]

@Steve252 

The iPhones are most likely using MAC address randomisation, which means that the MAC address will change each time they visit.

The home hub would then allocate a new IP address to the iPhone, as it thinks its a new device.

Here is a related post https://community.bt.com/t5/Home-setup-Wi-Fi-network/Private-Address-MAC-Randomisation-IOS14-Apple-d...

From Apple https://support.apple.com/en-gb/guide/iphone/iph6b324bb33/ios

It totally defeats any form of access control which is based on the MAC address.

[licquorice]

No idea why you consider it to be  a problem. If you have devices that you need to have consistent IP addresses, give them static addresses outside of the DHCP range of the hub on the devices themselves.

[rbz5416]

As @licquorice said, the proper way to do it is to set static IP addresses on your devices. IIRC, the DHCP range on BT Hubs starts at 192.168.1.64, so you can use any address below that & it will never change or be allocated elsewhere.

[Steve252]

Hi All,

Yes I'm fully aware about the static addresses but the problem is that the dhcp server of the BT is failing it own rules and is why I was asking if anybody else was aware of the problem with iphones and it only effects them.

On the bt modem you can set the ip address so that the device 'should' use the same IP address, the iphone is not using random mac address as the displayed mac address of the iphone is the same each time.

BT support have said that they cannot help solve it.

[Steve252]

PS the dhcp range does not start at 64 in my case, done delibrately so I know at a glance why device is connected, then I see an 'unknown device mac address' when the mac address is the known one.