# iptables -L -n -v
# iptables -L -n -v --line-numbers
# iptables -L INPUT -n -v
# iptables -L OUTPUT -n -v --line-numbers
#2: Stop / Start / Restart the Firewall
If you are using CentOS / RHEL / Fedora Linux, enter:
# service iptables stopDelete all rule
# service iptables start
# service iptables restart
# iptables -F
#3: Delete Firewall Rules
Get line numbers
# iptables -L INPUT -n --line-numbersAnd delete
# iptables -L OUTPUT -n --line-numbers
# iptables -L OUTPUT -n --line-numbers | less
# iptables -L OUTPUT -n --line-numbers | grep 202.54.1.1
# iptables -D INPUT 4
#4: Insert Firewall Rules
To insert one or more rules in the selected chain as the given rule number use the following syntax. First find out line numbers, enter:
# iptables -L INPUT -n –line-numbersSample outputs:
Chain INPUT (policy DROP)To insert rule between 1 and 2, enter:
num target prot opt source destination
1 DROP all -- 202.54.1.1 0.0.0.0/0
2 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state NEW,ESTABLISHED
# iptables -I INPUT 2 -s 202.54.1.2 -j DROP
To view updated rules, enter:
# iptables -L INPUT -n --line-numbers
Sample outputs:
Chain INPUT (policy DROP)
num target prot opt source destination
1 DROP all -- 202.54.1.1 0.0.0.0/0
2 DROP all -- 202.54.1.2 0.0.0.0/0
3 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
#5: Save Firewall Rules
# service iptables save#6: Restore Firewall Rules
To restore firewall rules form a file called /root/my.active.firewall.rules, enter:
# iptables-restore < /root/my.active.firewall.rules
#7 Block or Open Common Ports
The following shows syntax for opening and closing common TCP and UDP ports:
Replace ACCEPT with DROP to block port:
## open port ssh tcp port 22 ##
iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 22 -j ACCEPT
## open cups (printing service) udp/tcp port 631 for LAN users ##
iptables -A INPUT -s 192.168.1.0/24 -p udp -m udp --dport 631 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -p tcp -m tcp --dport 631 -j ACCEPT
## allow time sync via NTP for lan users (open udp port 123) ##
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p udp --dport 123 -j ACCEPT
## open tcp port 25 (smtp) for all ##
iptables -A INPUT -m state --state NEW -p tcp --dport 25 -j ACCEPT
# open dns server ports for all ##
iptables -A INPUT -m state --state NEW -p udp --dport 53 -j ACCEPT
iptables -A INPUT -m state --state NEW -p tcp --dport 53 -j ACCEPT
## open http/https (Apache) server port to all ##
iptables -A INPUT -m state --state NEW -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -m state --state NEW -p tcp --dport 443 -j ACCEPT
## open tcp port 110 (pop3) for all ##
iptables -A INPUT -m state --state NEW -p tcp --dport 110 -j ACCEPT
## open tcp port 143 (imap) for all ##
iptables -A INPUT -m state --state NEW -p tcp --dport 143 -j ACCEPT
## open access to Samba file server for lan users only ##
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 137 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 138 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 139 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 445 -j ACCEPT
## open access to proxy server for lan users only ##
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 3128 -j ACCEPT
## open access to mysql server for lan users only ##
iptables -I INPUT -p tcp --dport 3306 -j ACCEPT
#8 Allow IP access to PORT
#iptables -A INPUT -p tcp -s YourIP --dport 22 -j ACCEPT#Iptables allow or block ICMP ping request
#iptables -A INPUT -p tcp -s 0.0.0.0/0 --dport 22 -j DROP
#Allow
SERVER_IP="202.54.10.20"#Block
iptables -A INPUT -p icmp --icmp-type 8 -s 0/0 -d $SERVER_IP -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
iptables -A OUTPUT -p icmp --icmp-type 0 -s $SERVER_IP -d 0/0 -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A OUTPUT -p icmp --icmp-type echo-request -j DROP
OR
iptables -A OUTPUT -p icmp --icmp-type 8 -j DROP
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