ferm.conf

# -*- shell-script -*-
#
#  Configuration file for ferm(1).
#

table filter {
    chain INPUT {
        policy DROP;

        # connection tracking
        mod state state INVALID DROP;
        mod state state (ESTABLISHED RELATED) ACCEPT;

        # allow local packet
        interface lo ACCEPT;

        # respond to ping
        proto icmp ACCEPT; 

        # allow SSH connections
        proto tcp dport ssh ACCEPT;

        # http https
        proto tcp dport (http https) ACCEPT;

        # snmp
        proto udp dport snmp ACCEPT;
    }
    chain OUTPUT {
        policy ACCEPT;

        # connection tracking
        #mod state state INVALID DROP;
        mod state state (ESTABLISHED RELATED) ACCEPT;
    }
    chain FORWARD {
        policy DROP;

        # connection tracking
        mod state state INVALID DROP;
        mod state state (ESTABLISHED RELATED) ACCEPT;
    }
}