How to block an IP Address on a Linux Server

Introduction

In order to block IP using iptables , you can execute following commands up on your condition.

• If you want to block an ip address from accessing your server then type the commands as follows:

iptables -A INPUT -s IP-ADDRESS -j DROP

Example :

iptables -A INPUT -s 10.10.10.10 -j DROP
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	service iptables save
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	service iptables reload

This command will block network connections originate from IP address – 10.10.10.10

• For block access to one port from an IP 10.10.10.10 to port 25

iptables -A INPUT -s 10.10.10.10 -p tcp --destination-port 25 -j DROP
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	service iptables save
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	service iptables reload

• To allow incoming ssh connections only from IP – 11.11.11.11 and block all other IPs.

iptables -A INPUT -p tcp --dport 22 -s 11.11.11.11 -j ACCEPT
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	iptables -A INPUT -p tcp --dport 22 -j DROP
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	service iptables save
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	service iptables reload

You can use following commands to block IP address to access the server using ConfigServer Security & Firewall (CSF).

The IP will be added to the block list – /etc/csf/csf.deny file If you block the IP using CSF.

• Permanently blocking an IP address from accessing the server.

csf -d IPaddress
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	service csf restart

Example – Block IP address 10.10.10.10 to access the server.

csf -d 10.10.10.10

• Temporarily block an IP address from accessing the server.

csf -td IPaddress ttl

Example – Block the IP address 10.10.10.10 temporarily (1 hour )to access the server.

csf -td 10.10.10.10

Block the IP address 10.10.10.10 temporarily (2 hour )to access the server

root@web22 [~]# csf -td 10.10.10.10 7200
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	DROP  all opt -- in !lo out *  10.10.10.10  -> 0.0.0.0/0
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	csf: 10.10.10.10 blocked on port * for 7200 seconds inbound

Important CSF Commands

csf -s- Start the firewall rules

csf -f- Flush/Stop firewall rules

csf -r- Restart the firewall rules

csf -e- Enable the firewall rules

csf -x- Disable the firewall rules

csf -a IPaddress - Allow an IP address in server firewall

csf -td IPaddress ttl - Block an IP (by default - 1 hour ) temporarily

csf -tr IPaddress - Remove an IP from the temporary IP ban or allow list.

csf -d IPaddress - Deny an IP.

csf -dr IPaddress - Remove an IP from the firewall blocklist.