alpine-server-setup/services/firewall/icmp.policy.json

{
    "description": "Allow ping-pong",
    "filter": [
        {
            "in": "WAN",
            "out": "_fw",
            "service": "ping",
            "action": "accept",
            "flow-limit": { "count": 10, "interval": 6 }
        }
    ]
}