I've had a look at those two FAQs. I'd thought that it was done using ICMP6 requests, but not seeing any threw me. I decided to do the following: 1). Start a rate-limited download over IPv6 so that traffic would be going through the tunnel continuously during the test 2). Execute tcpdump -ni em0 proto 41 to capture the 6in4 traffic. 3). Execute tcpdump -ni gif0 icmp6 to capture the icmp6 traffic. 4). SSH to my home network (over IPv4) and ping the IPv6 address of gif0 (90s interval). What I saw: 1). Every 40s, an ICMP6 neighbor solicitation was sent to the POP, every single one was replied to. 2). Every 90s, I saw the ICMP6 echo request from my home network, every single echo request was replied to. 3). This is where it gets a bit strange. After a period, I started to see ICMP6 echo requests from the POP, for every request, a reply was sent. The successful pinging goes on for about 5 minutes, then it stops. I see no incoming ping requests from the POP for about 25 minutes. Then the pinging starts again, for 5 minutes. This cycle continues. I can discount pfctl being the issue: 1). It's configured to allow inbound ICMP6 traffic. 2). Inbound ICMP6 traffic from my home network has no loss. 3). Configuring pfctl to allow all in on gif0 makes no difference. The obvious cause of the issue would be the DMZ mode not working. However I'm not convinced it can be the cause. What I find incredibly strange is how the POP echo requests stop and start periodically, but the other echo requests have no issues whatsoever.