General iptables firewall rules and commands
Today we are going to show you some general firewall rules and commands in iptables. Iptables is a useful command line utility for configuring the Linux kernel firewall. Iptables contains five tables: raw, filter, nat, mangle, and security. Each table is made up of chains. A chain is a list of firewall rules that follow in order. Let’s start with some general iptables firewall rules and commands.
Install iptables
Log into your VPS via SSH as root user:
ssh [email protected]_Address -p Port_number
Installing iptables is very easy. If you have an Ubuntu VPS or Debian VPS, run the following commands:
apt-get update apt-get upgrade apt-get install iptables iptables-persistent
If you have CentOS or Fedora installed on your VPS, run the following commands:
yum clean all yum update yum install iptables
That’s it, you should now successfully install iptables on your server.
General iptables firewall rules
The following are examples of common firewall rules. Accept all ESTABLISHED and RELATED packages:
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
Allow HTTP and HTTPS connections from anywhere:
iptables -A INPUT -p tcp --dport 80 -j ACCEPT iptables -A INPUT -p tcp --dport 443 -j ACCEPT
Allow access to port 21 only from a specific IP address (for example, 192.168.1.123) and block access from all other IP addresses to the server (for example, the server IP address 192.168.1.100):
iptables -A INPUT -s 192.168.1.123 -d 192.168.1.100 -p tcp -m state --state NEW -m tcp --dport 21 -j ACCEPT iptables -A INPUT -d 192.168.1.100 -p tcp -m tcp --dport 21 -j DROP iptables-save
Block IP address (e.g. 192.168.1.21):
iptables -A INPUT -s 192.168.1.21 -j DROP
Block the IP range and reject all packets (e.g. 192.168.1.0/24):
iptables -A INPUT -s 192.168.1.0/24 -j REJECT
To block outgoing traffic to a port (for example port 123) use:
iptables -A OUTPUT -p tcp --dport 123 -j DROP
General iptables commands
List all rules in all chains in verbose mode and show IP addresses and port numbers instead of host and service names, including the interface name, rule parameters (if any), and TOS masks:
iptables -nvL | less
Chain INPUT (policy ACCEPT 17M packets, 3161M bytes)
pkts bytes target prot opt in out source destination
90M 18G cP-Firewall-1-INPUT all -- * * 0.0.0.0/0 0.0.0.0/0
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 cP-Firewall-1-INPUT all -- * * 0.0.0.0/0 0.0.0.0/0
Chain OUTPUT (policy ACCEPT 16M packets, 5107M bytes)
pkts bytes target prot opt in out source destination
0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 multiport dports 25,465,587 owner GID match 32006
18618 9100K ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 multiport dports 25,465,587 owner GID match 12
0 0 ACCEPT tcp -- * * 0.0.0.0/0 127.0.0.1 multiport dports 25,465,587 owner UID match 32001
10686 946K ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 multiport dports 25,465,587 owner UID match 0
Chain cP-Firewall-1-INPUT (2 references)
pkts bytes target prot opt in out source destination
39 2264 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:993
54 2872 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:53
7509 450K ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:21
557K 34M ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:443
19655 1142K ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:80
1057 43388 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:8080
7533 452K ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:143
382 16664 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
2871K 173M ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:995
23539 1284K ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:110
8353 500K ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:25
71 3680 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:465
519K 31M ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:3306
132 9948 ACCEPT udp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:53
To display rules in chains with rule numbers, use:
iptables -nvL --line-numbers
This is useful if you want to remove a rule (for example, remove rule number 9 from the INPUT chain):
iptables -D INPUT 9
Or add a rule between two existing rules (for example, add a firewall rule between rules # 2 and 3):
iptables -I OUTPUT 3 -d 127.0.0.1/32 -p tcp -m multiport --dports 25,465,587 -m owner --uid-owner 201 -j ACCEPT
To list all the commands that were used to create the currently used iptables rules, use the following command:
iptables -S
This command is useful if you need to edit or remove some of the firewall rules.
-P INPUT ACCEPT -P FORWARD ACCEPT -P OUTPUT ACCEPT -N cP-Firewall-1-INPUT -A INPUT -j cP-Firewall-1-INPUT -A FORWARD -j cP-Firewall-1-INPUT -A OUTPUT -p tcp -m multiport --dports 25,465,587 -m owner --gid-owner mailman -j ACCEPT -A OUTPUT -p tcp -m multiport --dports 25,465,587 -m owner --gid-owner mail -j ACCEPT -A OUTPUT -d 127.0.0.1/32 -p tcp -m multiport --dports 25,465,587 -m owner --uid-owner cpanel -j ACCEPT -A OUTPUT -p tcp -m multiport --dports 25,465,587 -m owner --uid-owner root -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 993 -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 53 -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 21 -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 443 -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 8080 -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 143 -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 995 -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 110 -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 25 -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 465 -j ACCEPT -A cP-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 3306 -j ACCEPT -A cP-Firewall-1-INPUT -p udp -m state --state NEW -m udp --dport 53 -j ACCEPT
Clear all firewall rules:
iptables -F
Use ‘iptables -h | less’ for more information on all the options for the iptables command.