linux + firewall + how to check if any port on linux is blocked by the firewall / iptables

Question

some application on my redhat Linux machine isn't working ( and we suspect that according to application logs some port's are blocked )

so we want to check all ports on the OS that are blocked by the Firewall/iptables

is it possible to scan/verify all ports ( lets say from /etc/services ) on the linux OS and verify ports that are blocked ?

Solution

You can just dump the firewall rules your machine runs:

sudo iptables -S

If you use firewalld on RHEL7, you can use

sudo firewall-cmd --list-all-zones

for a more readable output.

Comments

[Daniel Widrick]

Why don't you ask the sysadmin which ports are blocked or tell that person to unblock the ports that your application uses?