How to check if a port is allowed in iptables?

thomas2004ch · 08-23-2010, 03:41 AM

I want to check if a port is allowed in iptables. How to do this?

chrism01 · 08-23-2010, 04:00 AM

iptables -L

as root user

thomas2004ch · 08-23-2010, 04:18 AM

Quote:

Originally Posted by chrism01

iptables -L

as root user

I got followings:

Code:

[root@s003ap25-test ~]# iptables -L
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

Assumed I will check the port 8999 is allowed in the iptables, how can I do this?

blue_print · 08-23-2010, 04:28 AM

You do not have any rules configured in Iptables. It is showing empty table. To check the opened ports in iptables, you may use the following command,

iptables -nL | grep <port number>

thomas2004ch · 08-23-2010, 04:38 AM

I type

iptables -nL | grep 8999

But I get nothing shown. What does this mean?

Then I try and iptables -nL. But still nothing shown.

blue_print · 08-23-2010, 04:41 AM

As I said already, the iptables in your system doesn't have any rules configured. For this reason, you are not getting anything after executing "iptables -nL | grep 8999".

You may refer the link http://www.linuxhomenetworking.com/w...Using_iptables

to configure iptables rules in your system.

RevelationNow · 10-10-2017, 11:24 PM

Quote:

Originally Posted by blue_print

As I said already, the iptables in your system doesn't have any rules configured. For this reason, you are not getting anything after executing "iptables -nL | grep 8999".

You may refer the link [Ironically this message board won't allow me to quote a link]

to configure iptables rules in your system.

So, the way Grep works, is it will filter an output to only show lines containing your search criteria.

The way that IPTables -nL works is that it will list the target, protocol, source and destination, but doesn't list the port information for any of those rules.

So, the question remains, how can we see the port information? I don't think Grep is going to help on this output since the output doesn't contain the single detail we are searching for.

RevelationNow · 10-10-2017, 11:28 PM

Quote:

Originally Posted by thomas2004ch

I want to check if a port is allowed in iptables. How to do this?

iptables -S

rknichols · 10-11-2017, 09:17 AM

Quote:

Originally Posted by thomas2004ch

I got followings:

Code:

[root@s003ap25-test ~]# iptables -L
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

Assumed I will check the port 8999 is allowed in the iptables, how can I do this?

None of the chains have any rules, so they all fall through to their default policy of "ACCEPT". Everything is accepted.