I have set the Reply to ICMP Ping to YES and get responses from outside the network.
When I set the Reply to ICMP Ping back to NO, Save and Apply Changes, I still get ping responses from outside the network.
What type of WAN link is it? Could the next hop router be the device that replying?
That might be the situation. It is a static IP on our ISPs network. It might be their equipment responding.
I have not seen this behavior before, but this is the first time I am checking with this ISP.
you could prove it by running a network capture on the peplink and seeing if the icmp packets actually hit its wan interface or not…
In addition to what @MartinLangmaid suggested you could also disconnect your Peplink router from the modem/CPE/whatever else you have attached to the Peplink router’s WAN port and then ping it using another connection, e.g., cellular.