[kea-dev] More Kea/OpenWRT integration

[Philip Prindeville]

> On Jan 29, 2026, at 12:58 PM, Morten Brørup <mb at smartsharesystems.com> wrote:
> 
>> On OpenWRT we support a host having multiple MAC addresses for the same
>> IP, to allow people to have laptops with docking stations and WiFi and
>> to roam without losing connectivity.
> 
> I'm sorry if my question is off-topic, but this scenario got me really curious!
> 
> Can you please elaborate about how having the same IP address on Ethernet and Wi-Fi works on the laptop?
> 
> Are both interfaces on the laptop active at the same time?
> How does the laptop respond to ARP?
> Is it controlled by the "metric" on the laptop's route table, or does it respond to ARP depending on the interface where the ARP request was received, or something else?
> 
> Which laptop operating systems does it work with? Windows? Mac? Linux?
> 
> -Morten
> 


I can't tell you how all systems will behave, but I do know that the Linux IP neighbor table caches the interface associated with an ARP query (as well as the interface, IP and MAC of the requestor as an optimization).

It's not ARP that's driving this, though, it's DHCP.  Whenever carrier on an interface flaps and that interface is configured to use DHCP, a DHCP request will be sent on that interface, or the DHCP settings on that interface will be scrubbed (for up and down transitions, respectively).

Typically Ethernet has a better metric than WiFi, so even if both are up your docking station will be preferred if it has carrier (i.e. is connected).