How To Install and Use Iptables on AlmaLinux 8

In this guide, we want to teach you How To Install and Use Iptables on AlmaLinux 8.

Simply put, iptables is a firewall program for Linux. It will monitor traffic from and to your server using tables. These tables contain sets of rules, called chains, that will filter incoming and outgoing data packets.

When a packet matches a rule, it is given a target, which can be another chain or one of these particular values:

• ACCEPT – will allow the packet to pass through.
• DROP – will not let the packet pass through.
• RETURN – stops the packet from traversing through a chain and tells it to return to the previous chain.

Steps To Install and Use Iptables on AlmaLinux 8

To complete this guide, you must log in to your server as a non-root user with sudo privileges. To do this, you can follow our guide the Initial Server Setup with AlmaLinux 8.

Install Iptables Firewall on AlmaLinux 8

First, update your local package index with the following command:

sudo dnf update

By default, iptables come pre-installed in most Linux distributions.

If you don’t have it, then, you can use the following command to install an iptables firewall on your server:

sudo dnf install iptables-services

Verify your Iptables installation by using the command below:

sudo rpm -qa | sudo grep -i iptables-services

Output
iptables-services-1.8.4-22.el8.x86_64

Manage Iptables Service

At this point, you can use the command below to start Iptables on AlmaLinux 8:

sudo systemctl start iptables

To enable it to start on boot, use the command below:

sudo systemctl enable iptables

Verify that the Iptables service is active and running on AlmaLinux 8:

sudo systemctl status iptables

In your output you will see:

Output
● iptables.service - IPv4 firewall with iptables
   Loaded: loaded (/usr/lib/systemd/system/iptables.service; enabled; vendor pr>
   Active: active (exited) since Sat 2022-10-08 06:30:47 EDT; 10s ago
 Main PID: 39471 (code=exited, status=0/SUCCESS)
    Tasks: 0 (limit: 23668)
   Memory: 0B
   CGroup: /system.slice/iptables.service
...

Check iptables Configuration

At this point, you can check your iptables configuration with the following command:

sudo iptables -L -v

• The -L parameter is for the list of all rules, and the -v parameter is used to show information in more detail.

In your output you will see:

Output
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination 
   19  1348 ACCEPT     all  --  any    any     anywhere             anywhere             state RELATED,ESTABLISHED
    0     0 ACCEPT     icmp --  any    any     anywhere             anywhere    
    0     0 ACCEPT     all  --  lo     any     anywhere             anywhere    
    0     0 ACCEPT     tcp  --  any    any     anywhere             anywhere             state NEW tcp dpt:ssh
   12   617 REJECT     all  --  any    any     anywhere             anywhere             reject-with icmp-host-prohibited

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination 
    0     0 REJECT     all  --  any    any     anywhere             anywhere             reject-with icmp-host-prohibited

Chain OUTPUT (policy ACCEPT 24 packets, 3007 bytes)
 pkts bytes target     prot opt in     out     source               destination 

Now that you have installed iptables on AlmaLinux 8, let’s do some basic usage of it.

How To Use iptables on AlmaLinux 8

In this part, we intend to show you some basic usage of iptables on your server.

You can use iptables to define a rule. It means that you can append it to the chain.

To do this, you can use the -A parameter after the iptables command on AlmaLinux 8 as shown below:

sudo iptables -A [argument]

Also, you can combine the command with other parameters like:

• -i: the network interface whose traffic you want to filter, such as eth0, lo, ppp0, etc.
• -p:  the network protocol where your filtering process takes place. It can be either TCP, UDP, udplite, ICMP, SCTP, icmpv6, and so on. Also, you can type all to choose every protocol.
• -s: the address from which traffic comes. You can add a hostname or IP address.
• -dport: the destination port number of a protocol, such as 22 (SSH), 443 (https), etc.
• -j:  the target name (ACCEPT, DROP, RETURN). You need to insert this every time you make a new rule.

Note: If you want to use all of the parameters, you need to type the iptables command on AlmaLinux 8 in the order shown below:

sudo iptables -A <chain> -i <interface> -p <protocol (tcp/udp)> -s <source> --dport <port no.>  -j <target>

To allow traffic on localhost, you can use the iptables firewall command like the below command:

sudo iptables -A INPUT -i lo -j ACCEPT

You can enable a connection like SSH on iptables command like this:

sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

Then, you can check the rule that has been appended in iptables on AlmaLinux 8 with the command below:

sudo iptables -L -v

In your output you will see:

Output
0 0 ACCEPT tcp -- any any anywhere anywhere tcp dpt:ssh

Iptables allow you to filter packets on an IP address or a range of IP addresses. To do this, you need to use the -s parameter in the iptables command on AlmaLinux 8. For example:

sudo iptables -A INPUT -s 10.10.0.1 -j ACCEPT

You can also reject the packets with the command below:

sudo iptables -A INPUT -s 10.10.0.1 -j DROP

Also, you can drop all other traffic simply by using the following command:

sudo iptables -A INPUT -j DROP

To delete all current rules on your iptables firewall you can use the following command:

sudo iptables -F

To delete a specific rule, you need to first check the available rules of iptables on AlmaLinux 8 by typing the following command:

sudo iptables -L --line-numbers

In your output you will see:

Output
num  target     prot opt source               destination
1    ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
2    ACCEPT     icmp --  anywhere             anywhere
3    ACCEPT     all  --  anywhere             anywhere
4    ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh
5    REJECT     all  --  anywhere             anywhere             reject-with icmp-host-prohibited
6    ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ssh

Here to delete a specific rule, you also need to specify the rule number in the command below:

sudo iptables -D INPUT 4

To apply the changes that have been saved on boot you can use the following command:

sudo /sbin/iptables-save

Disable iptables

If you want to disable iptables, you can use the following commands:

$ sudo iptables -F
$ sudo /sbin/iptables-save

In your output you will see:

Output
:INPUT ACCEPT [19:2597]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [6:528]
...

If you want to find more detailed information about iptables and their options it is highly recommended to read its manual:

man iptables

Conclusion

At this point, you have learned to Install and Use Iptables on AlmaLinux 8.

Hope you enjoy it.

For more guides and articles, you can visit the OrcaCore website.