Wan Arp conflict issues causing loss of network

[Darkvader]

Hi Everyone, a bit of a weird question.

My modem does dynamic Local and public DHCP allocation for the WAN address and opnsense gets a bit in a twist with it.

What it does is when the modem is powered on the device connected to it (opnsense here) is given a local address (192.168.100.x in this case) and then when the modem itself is allocated a public address it will do a bit of a handshake then do a quick swap so the opnsense box has the public IP and can communicate directly.

Where it gets a bit funky is that Opnsense regularly thinks there's a conflict with arp, will start ignoring DHCP addresses and then will lose all WAN connectivity.

here's a line from the log:

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<3>[67488] arp: 4x:8x:cx:8x:3x:7x is using my IP address 18x.2x.1x.5x on igb0!that MAC is the modems MAC address, so it's successfully telling opnsense the public ip, but opnsense thinks there's something wrong and will refuse to use it.
Is there a way to turn off the arp ip collision stuff, it's seriously causing a headache with this handover.

the way i've worked around it for now is to set the WAN address staically to a 192.168.100.x address, which isn't ideal as it now means i'm double NAT'ed.