How to block the ip addresses using iptables. Can any one tell me the rule to block specific ip address/addresses of more than one machine
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The rule to drop an IP address can be really simple:
However, in general it is a MUCH better approach to drop all IP addresses and then adjust the firewall to only allow the traffic you want. Depending on what you're trying to do, dropping individual IP addresses might not be the best approach.

Hangdog42,

No interface (--i ethx) is mentioned in the rule. Just curious to know absence of nic card does not make any difference?. It will grate help if you can explain what will happen in both cases. Means if nic card is listed an NOT listed in rule.

Thanks in advance

onlymahendra7,

Assume, you are root user & wanted to block IP Address: 123.123.123.123

^ To Block/Ban IP Address
# iptables -A INPUT -s 123.123.123.123 -j DROP
# service iptables save

^ If needed, restart iptables.
# service iptables restart

^ Check blocking worked or not!
# netstat -n | grep 123.123.123.123


PS: If you want to block whole range, use subnet parameter like 123.123.0.0/16 OR 123.123.0.0-123.123.255.255

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If you are dropping an IP address you most likely want to drop everything, the above rule will only drop tcp packets. UDP/ICMP etc will still get through.
This is usually not an option for a publicly facing server, This is where fail2ban comes into play, fail2ban monitors logs and dynamically creates iptables rules based on certain conditions, $x number of connection attempts per minute, etc.
One would only need to match by interface if the box was acting as a router with multiple interfaces.

But if you want to drop everything from a particular IP address, you want to do it regardless of the interface, in the interests of keeping rules simple there is no need to use unnecessary matches, which only adds confusion.
As Mayur Pipaliya suggested.
Will drop any packets coming INTO the firewall, from anywhere, on any interface where the packet has a source IP address of 1.1.1.1.

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fukawi1,

Awesome!,
Thanks for nice explanation