[edit security nat]
source {
    rule-set trust-to-untrust {
        from zone trust;
        to zone untrust;
        rule source-nat-rule {
            match {
                source-address 0.0.0.0/0;
                destination-address 0.0.0.0/0;
            }
            then {
                source-nat {
                    interface;
                }
            }
        }
    }
    rule-set external-to-untrust {
        from zone external;
        to zone untrust;
        rule external-nat-rule {
            match {
                source-address 0.0.0.0/0;
                destination-address 0.0.0.0/0;
            }
            then {
                source-nat {
                    interface;
                }
            }
        }
    }
}
[edit security policies]
from-zone trust to-zone untrust {
    policy trust-to-untrust {
        match {
            source-address any;
            destination-address any;
            application any;
        }
        then {
            permit;
        }
    }
}
from-zone external to-zone untrust {
    policy external-to-untrust {
        match {
            source-address any;
            destination-address any;
            application any;
        }
        then {
            permit;
        }
    }
}