The original post says that your router is pinging the gateway. Then later you say that somebody else (from iran) is pinging your router. Which one is it?
It all started because of flood pings from Iran and Germany slowing down the network.
According to the logs it initially looked as if the RB was pinging the gateway that is because of the way they are written out, then I noticed that it was type 0 a reply, so checked logs for type 8 request from gateway and yes it was the gateway pinging the RB but when I put block rule on WAN, the internet went off and all my PPPoE users connection started dropping out.
**I have never come across blocking ping replies on WAN causing internet drop out, so I had not got a clue at first what was going on.
In the meantime I just blocked ping replies to the attackers.
Once I new it was pings from the gateway I contacted supplier, they confirmed that they do ping it and if it gets block the internet may not work, they only said may not work.
Once I new this I put in an accept rule for the gateway and an accept with limit rule for everything else to put a load on their device.
There is now a full block rule on for everything else except the gateway.
***I still have no idea why the block rule should stop the internet and cause PPPoE connections to drop