Block an IP Address on My Linux server

How Do I Block an IP Address on My Linux server?

How do I block an IP address or subnet under Linux operating system?

In order to block an IP on your Linux server you need to use iptables tools (administration tool for IPv4 packet filtering and NAT) and netfilter firewall. First you need to log into shell as root user. To block an IP address you need to type the iptables command as follows:

Syntax to block an IP address under Linux

For example, if you wish to block an ip address 65.55.44.100 for whatever reason then type the command as follows:

# iptables -A INPUT -s 65.55.44.100 -j DROP
If you have IP tables firewall script, add the above rule to your script.

If you just want to block access to one port from an ip 65.55.44.100 to port 25 then type command:
# iptables -A INPUT -s 65.55.44.100 -p tcp --destination-port 25 -j DROP
The above rule will drop all packets coming from IP 65.55.44.100 to port mail server port 25.

CentOS / RHEL / Fedora Block An IP And Save It To Config File
Type the following two command:
# iptables -A INPUT -s 65.55.44.100 -j DROP
# service iptables save
How Do I Unblock An IP Address?
Use the following syntax (the -d options deletes the rule from table):
# iptables -D INPUT -s xx.xxx.xx.xx -j DROP
# iptables -D INPUT -s 65.55.44.100 -j DROP
# service iptables save

Allow specify port using iptables

/sbin/iptables -I INPUT -p tcp --dport 80 -j ACCEPT
# 儲存設定
/etc/rc.d/init.d/iptables save
# 重新啟動防火牆
/etc/init.d/iptables restart


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