Iptables rules should always start with dport ?

[linuxcenter]

for eg : to Allow Outgoing HTTPS

iptables -A OUTPUT -o eth0 -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT
(why its dport to sport )

can we convert the rule to this
iptables -A OUTPUT -o eth0 -p tcp --sport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --dport 443 -m state --state ESTABLISHED -j ACCEPT

( why not sport to dport)

[mlu17]

Hi,

the following line indicates that we want to allow the outoing HTTS traffic coming (dport = destination port) from port 443

iptables -A OUTPUT -o eth0 -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT

and this line indicates that every connection that we made already (sport = source port) from port 443 (the line above) will also be allowed to go the other way around -> incoming traffic (but not ALL incoming traffic, only the ones which are due to our outgoing connection).

iptables -A INPUT -i eth0 -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT

hope that kind of clarifies what you want to know

Regards,
Michael

[m4nd4r]

OUTPUT and dport combination stands for those packets leaving the system and destined for port 443 of remote system.
INPUT and sport combination stands for those packets arriving to the system and originating from port 443 of remote system.

OUTPUT and sport combination will be applicable for those packets leaving port 443 of your system.
INPUT and dport combination will be applicable to packets destined for port 443 of your system.

You can use any combination depending on your application.

To know more about IPTables, Visit - IPTables-Linux Firewall