nc command and iptables on CentOS7

Question

I have practised in using iptables on CentOS 7 (It is a guest machine on Virtual Box). At first I disabled firewalld:

systemctl disable firewalld
systemctl stop firewalld

Then I installed iptables:

yum -y install iptables-services
systemctl enable iptables
systemctl start iptables

After all this I tried to open tcp-port on my local machine with nc -l 1025 command but command just hung up. I was looking all over the Internet and found out that I could flush iptables rules in this post The netcat command can't access an open port but after this I had no connection to the Internet at all. So I returned my CentOS7 in previous state when I had just installed iptables. Here is my iptables's rules:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere             state    RELATED,ESTABLISHED
ACCEPT     icmp --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp    dpt:ssh
REJECT     all  --  anywhere             anywhere             reject-with icmp-host-prohibited

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
REJECT     all  --  anywhere             anywhere             reject-with  icmp-host-prohibited

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

Here is the verbose mode of nc -vl 1025:

Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Listening on :::1025
Ncat: Listening on 0.0.0.0:1025

And the result of ss -lnt:

State      Recv-Q Send-Q        Local Address:Port          Peer    Address:Port
LISTEN     0      128                       *:22                       *:*
LISTEN     0      100               127.0.0.1:25                       *:*
LISTEN     0      128                      :::22                      :::*
LISTEN     0      100                     ::1:25                      :::*

Another verbose mode for example for port 2000 nc -vl 2000:

Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Listening on :::2000
Ncat: Listening on 0.0.0.0:2000

the result of ss -lnt is the same:

State      Recv-Q Send-Q        Local Address:Port          Peer  Address:Port
LISTEN     0      128                       *:22                       *:*
LISTEN     0      100               127.0.0.1:25                       *:*
LISTEN     0      128                      :::22                      :::*
LISTEN     0      100                     ::1:25                      :::*

So what am I going to do to make my nc command works properly and I can open some tcp port on CentOS7?

Answer 1

Got solved in the comments - quick summary of the most important points:

• ncat, and possibly other netcat impletmentations, listens for incoming connection only once, and stops doing so with the first attempt (unless there's a switch in program for that)

• programs can start listening on a port regardless of what are the current iptables settings