MAC randomisation and DHCP pools

glenn.satchell at glenn.satchell at
Fri Jul 24 09:48:54 UTC 2020

Hi Mike,

This is not something new, it has been around since IOS 8 in 2014. I 
think this page summarises how it works and has links to Apple's site 
with more details.

It appears that it randomises the MAC address when the device is 
passively scanning for networks and other particular settings are 
enabled or disabled, so systems can't use the MAC address to 
persistently track wherever you go. However, it seems that any 
associations/joining of networks is based on the actual MAC address.

Or am I talking about something else entirely different?


On 2020-07-24 19:10, Mike Richardson wrote:
> Hiya,
> Given Apple's decision to enable randomisation of MACs on IOS devices 
> every
> 24 hours, I was wondering what effect this would have on DHCP?
> For example, if you have a pool of 100 IPs, 50 IOS devices and leases 
> set to
> 7 days.
> At the moment the same 50 IPs would be assigned each day. 
> Post-randomisation
> 50 would be assigned on day 1. On day 2, my understanding is that the 
> devices
> would REQUEST their previous IPs and be NACKed, then do a DISCOVER and 
> get a
> new lot of 50 addresses. What I'm unsure about is what happens on day 
> 3? 'no
> free leases', a ping check and reallocation of old addresses or 
> something
> else?
> Can anyone enlighten me?
> Thanks,
> Mike

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