[Dnsmasq-discuss] Block dhcp from serving to specific device

[dev at lutean.com]

I ran into this problem. There is no fix on the Apple side. Until iCloud 
Sync allows disabling syncing of wifi passwords it will keep happening.

One fix is to disable guests (dynamic addresses) on the parent network.

My fix was to add a feature to dnsmasq. The feature has been present in 
dnsmasq since 2.78. dnsmasq automatically adds a tag to a device that is 
roaming to a network other than the one it has a static lease on. The 
tag is 'known-othernet'. Since you have static leases for the kids 
devices, when they try and register on the parent vlan, the 
'known-othernet' tag will be present. You can ignore dhcp requests when 
the 'known-othernet' tag is present with

dhcp-ignore=tag:known-othernet

Of course, once your kids update to iOS14 you will also have to disable 
the private MAC feature that gets turned on by default.

I have submitted another patch request through the mailing list to 
handle that problem, but it has not yet been accepted into the official 
release.

Todd