recipes-google/s4/gpowerd/43-gbmc-gpowerd.rules

table inet filter {
    chain gbmc_br_pub_input {
        tcp dport 20120 accept
    }
    chain count_port_20120 {
        counter comment "tcp-server-20120-synack"
    }
}

add element inet filter port_to_chain_map { 20120 : jump count_port_20120 }