How to open a port? 3000

[peopleinside]

Hi, I'm experiencing issue on opening a port.
I'm on Centos 7.x

I followed all guides found on Google but still not able to open port 3000
On Centos 7 seems you have to use firewall-cmd but is not installed on my server so i suppose if the port is not open is not closed by this but from iptables.

I tried

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iptables -A INPUT -i eth0 -p tcp --dport 3000 -j ACCEPT

saved and restarted iptables but nothing port still be seen closed.

Any idea?
I cannot understand...

In the oputput of iptables-save I have:

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-A OUTPUT ! -o lo -p tcp -m state --state NEW -m tcp --dport 3000 -j ACCEPT
-A INPUT ! -i lo -p tcp -m state --state NEW -m tcp --dport 3000 -j ACCEPT

checking the port still be closed.

[TrevorH]

If you're not using firewalld tehn you are probably using plain iptables. If so then the rule you added went at the end of the chain, after the final existing one that rejects all connections so it would never be used. You need to `iptables -I INPUT nn` insert the rule at line number nn.

[peopleinside]

Thanks for the reply. Can you suggest steps to do?
Sorry

I have to print a list with a command than find the right line and do the command with the desired line?
I do in the past but i cannot remember steps to do.
Thanks

[jlehtone]

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iptables --lin -nL

[peopleinside]

Thanks, now i see the lines with iptables --lin -nL what to do?
>.<

I used now:

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iptables -I INPUT -m state --state NEW -p tcp --dport 3000 -j ACCEPT

saved, and restarted iptables still not working.

[jlehtone]

-I, --insert chain [rulenum] rule-specification
Insert one or more rules in the selected chain as the given rule number. So, if the rule number is 1,
the rule or rules are inserted at the head of the chain. This is also the default if no rule number is
specified.

You did not specify rule number. Therefore, you did use:

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iptables -I INPUT 1 -m state --state NEW -p tcp --dport 3000 -j ACCEPT

What are your rules after restart? Show output of

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iptables -S INPUT

How do you determine whether something "works"?

[peopleinside]

With your command now the line are first.
I use https://ping.eu/port-chk/ still be closed.

[TrevorH]

You know that you also have to have something that listens on the port before it will appear to be open? What does ss -antup | grep 3000 say?

[peopleinside]

Said nothing, blank line.
I would like the port 3000 for NodeJS

[aks]

Start your app as you need a listener on port 3000.
ss -antl | grep 3000
to check the listener is established.
Then telnet (or whatever you want) to confirm you can connect to the port internally (and that something like SELinux is not tripping you up).
Then try from outside the machine to connect to that port, if it fails, switch the firewall off and try again. If it works, then the firewall is the problem, if it still doesn't work, there's a network problem.