iptables question.

Now for my system, I wrote down the following command when connection start,
in order to firewall my system and to enable NAT :

------->8 cut here start 8<------------------------
iptables -F; iptables -t nat -F; iptables -t mangle -F
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
echo 1 > /proc/sys/net/ipv4/ip_forward

iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -m state --state NEW -i ! ppp0 -j ACCEPT
iptables -P INPUT DROP # solo dopo che i due precedenti hanno avuto
successo
iptables -A FORWARD -i ppp0 -o ppp0 -j REJECT
------->8 cut here end 8<------------------------

And it's ok.
The problem is that it is a massive firewall, in the sense that if I try to
enter in my system from another remote system, I can't (I nether can do a
ping, to be honest ;-)
How can I do i I want, for example, make possible the connection from a
specific IP location and for a given port?
(Say, I want to let the IP 80.80.80.1 port 22 (ssh) enter in my system)
I made different experiments with no results..

Thanks in advance for any help (or URL/link on tutorial with pratical
example...)


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