How To List and Delete Iptables Firewall Rules in CentOS 7

Iptables is an essential and powerful tool for securing Linux based serverS. It is a command-line tool that allows you to configure packet filtering on Linux. If you are a system administrator and responsible for securing and managing firewalls, then you often need to list and remove unwanted Iptables rules from the Iptables. 

In this tutorial, we'll show you how to list and delete Iptables rules in CentOS 7. 

Requirements 

• A server running on CentOS 7.
• A root password configured on your server. 

List All Iptables Rules 

To list all Iptables rules by specification, run the following command: 

# iptables -S 

You should get the following output:

-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 443 -j ACCEPT

To list all rules from the specific chain like "INPUT" chain, run the following command: 

# iptables -S INPUT 

You should see the following output:

-P INPUT ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 443 -j ACCEPT

You can also list Iptables rules in a table view. It is very useful when you want to compare different rules against each other. 

# iptables -L

You should see the following output:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ssh
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:http
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:https

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination  

You can also filter the output to a specific chain with the following command: 

# iptables -L INPUT

This will list all rules in the "INPUT" chain:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ssh
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:http
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:https

You can use the option "-v" to list all rules with detail information including,  number of packages, and the aggregate size of the packages in bytes: 

# iptables -L INPUT -v 

You should see the following output:

Chain INPUT (policy ACCEPT 25 packets, 1096 bytes)
 pkts bytes target     prot opt in     out     source               destination         
  148 11064 ACCEPT     tcp  --  any    any     anywhere             anywhere             tcp dpt:ssh
    1    40 ACCEPT     tcp  --  any    any     anywhere             anywhere             tcp dpt:http
    0     0 ACCEPT     tcp  --  any    any     anywhere             anywhere             tcp dpt:https

Delete Iptables Rules

There are several ways you can delete the Iptables rules.

If you want to delete rules by chain and line number, you'll need to find the rule's line number first. You can list all rules by line number with the following command: 

# iptables -L INPUT --line-numbers

You should get the following output:

Chain INPUT (policy ACCEPT)
num  target     prot opt source               destination         
1    ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ssh
2    ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:http
3    ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:https

Next, you can delete rule "2" of the "INPUT" chain using the following command: 

# iptables -D INPUT 2

You can also delete the Iptables rules by the specification. If you want to delete the rules that drop the SSH packages, run the following command: 

# iptables -D INPUT -p tcp --dport 22 -j DROP

You can also delete the specific chain with all rules. For example, to delete all rules in the "OUTPUT" chain, use the following command:

# iptables -F OUTPUT

If you want to flush all chains and delete all rules, run the following command: 

# iptables -F

To flush and delete all "NAT" and "MANGLE" tables, run the following command: 

# iptables -F -t nat -v
# iptables -t mangle -F

Conclusion

In the above tutorial, you've learned how to list and delete Iptables rules in CentOS 7. We hope this will help you to delete unwanted Iptables rules from your system.