[plug] iptables questions

[Fred Janon]

Hi,

I am trying to understand how iptables work. I have a CentOS install and I am trying to enable ping/tracert on that instance. I don't understand if every port is open or closed by default on that instance? What does an empty rule mean? Every port opne or every port clodes?

And after I added the icmp rules, are other ports open or is icmp the only traffic allowed?

Here are the default iptables

---------------------------
$ sudo iptables -L -n
Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
--------------------------

After some research, I did this to try to enable PINGs. The server IP is 10.161.82.237

---------------------------
$ SERVER_IP="10.161.82.237"
$ sudo iptables -A INPUT -p icmp --icmp-type 8 -s 0                            /0 -d $SERVER_IP -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT

$ sudo iptables -A OUTPUT -p icmp --icmp-type 0 -s                             $SERVER_IP -d 0/0 -m state --state ESTABLISHED,RELATED -j ACCEPT

-------------------------------
Check the new tables
--------------------------------
$ sudo iptables -L -n
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     icmp --  0.0.0.0/0            10.161.82.237       icmp type 8 state NEW,RELATED,ESTABLISHED

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     icmp --  10.161.82.237        0.0.0.0/0           icmp type 0 state RELATED,ESTABLISHED

-----------------------------------

The tracert or ping still time out.

Thanks

Fred

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