iptables forward rulesets woes

["akshaysalkar" <akshaysalkar@indiatimes.com>]

i was refering to the book on linux net admin by olaf kirch
the example gives
'a organization having a firewall machine to allow internal users to be able to access WWW servers on the internet but no other traffic to be passed'
the iptable rules given are
iptables -F FORWARD
iptables -P FORWARD DROP
iptables -A FORWARD -m tcp -p tcp -s 0/0 --sport 80 -d 172.16.1.0/24 --syn -j DROP
iptables -A FORWARD -m tcp -p tcp -s 172.16.1.0/24  --sport 80 -d 0/0 -j ACCEPT
iptables -A FORWARD -m tcp -p tcp -d 172.16.1.0/24  --dport 80 -s 0/0 -j ACCEPT

i dont kinda understand this...
firstly 2nd line whats the -P. i guess its the default policy. but i could have given as
iptables -A FORWARD -j DROP

2nddly 3rd line why the -j DROP i thought it should be ACCEPT

3rdly since it says access the WWW servers on the internet why is it that on the 4th linethe --sport is 80
the source doesnt necessarily have to be 80 it could be any unprivileged port. the --dport should be infact 80

and the last line also seems confusing to me. where the -d is the network-ip

please help me/ suggest.

regards







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