Question

IPTables, blocking multiple ip addresses

Asked by: kapot

I am new to iptables.

What I need to do is, to block any access from some ip addresses.

I know that I can use: iptables -A INPUT -s <ip> -j drop

But then, I must write one by one for all ip addresses.

Is it possible to use something like a script ? so I just put all the ip addresses that I want to block into a file, for example blocked.txt

But I dont know how to start with iptables scripting.

Thanks for any help.

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Asked On
2003-07-18 at 15:38:51ID20683396
Tags

iptables

,

ip

,

block

Topic

Linux Network Security

Participating Experts
3
Points
30
Comments
9

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Answers

 

by: ahoffmannPosted on 2003-07-20 at 01:48:47ID: 8961126

# using a netmask:
iptables -A INPUT -s x.y.z.0/24 -j DROP
# using bash:
for i in `seq 5 1 8`; do iptables -A INPUT -s x.y.z.$i -j DROP; done

 

by: KlintanPosted on 2003-07-20 at 11:47:55ID: 8962762

Is this what you want?

---
#!/bin/bash

if [ -f badips.txt ]
then
        for BAD_IP in `cat badips.txt`
        do
                iptables -A INPUT -s $BAD_IP -j DROP
        done
else
        echo "Can't read badips.txt"
fi
---

However I would prefer that you set default policy to DROP and then only accept the god ones.
Something like this.

This asumes that your network is 192.168.0.x

---
iptables -F
iptables -t nat -F
iptables -t mangle -F

iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP

iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

iptables -A INPUT -i eth1 -p udp --dport bootps --sport bootpc -j DROP
iptables -A INPUT -i eth0 -p udp --dport bootps --sport bootpc -j ACCEPT
iptables -A OUTPUT -o eth1 -p udp --dport bootps --sport bootpc -j ACCEPT
iptables -A INPUT -m state --state ESTABLISHED -j ACCEPT
iptables -A OUTPUT -m state --state ESTABLISHED -j ACCEPT
iptables -A FORWARD -m state --state ESTABLISHED -j ACCEPT
iptables -A INPUT -m state --state RELATED -j ACCEPT
iptables -A OUTPUT -m state --state RELATED -j ACCEPT
iptables -A FORWARD -m state --state RELATED -j ACCEPT

iptables -A INPUT -s 192.168.0.0/24 -j ACCEPT

if [ -f godips.txt ]
then
        for GOD_IP in `cat godips.txt`
        do
                iptables -A INPUT -s $GOD_IP -j ACCEPT
        done
else
        echo "Can't read godips.txt"
fi
---

 

by: KlintanPosted on 2003-07-20 at 11:50:15ID: 8962768

Sorry. I'd copy_paste to much. Remove 3 lines

iptables -A INPUT -i eth1 -p udp --dport bootps --sport bootpc -j DROP
iptables -A INPUT -i eth0 -p udp --dport bootps --sport bootpc -j ACCEPT
iptables -A OUTPUT -o eth1 -p udp --dport bootps --sport bootpc -j ACCEPT

 

by: vbadierPosted on 2003-07-22 at 01:03:06ID: 8974321

Any more information are welcome.
ahoffmann and Klintan are right. However if you have a lots of different addresses, you will have as many rules as addresses in your table. Thus, your firewall will slow down since all packets will try to match all rules.

The best should be a range as specified by ahoffmann, butr this depend of your netword design and what you want to block.

So give us more information please.


Reagrd's

 

by: ahoffmannPosted on 2003-07-22 at 01:22:27ID: 8974413

> .. and then only accept the god ones.
how many millions are good ones? and which are the good ones?
or did you really mean "god ones"? Then there is only one, probably ...
Can you please be more specific :-]]

 

by: kapotPosted on 2003-07-23 at 22:47:59ID: 8992430

Yes, it's quite difficult if we drop everything and only accept a good one(s).
Because there are a lot of good ones.

The main reason I asking this was, I found a lot of strange IPs, scanning my web server. They tried to access unexisted cgi.
It's like a bot/scanner. I want to block this kind of access.

I like Klintan solution :

#!/bin/bash

if [ -f badips.txt ]
then
       for BAD_IP in `cat badips.txt`
       do
               iptables -A INPUT -s $BAD_IP -j DROP
       done
else
       echo "Can't read badips.txt"
fi

Because I can put all those scanners/bots IPs in that file, and RERUN the script.

 

by: vbadierPosted on 2003-07-24 at 01:16:57ID: 8993232

But what i don't understand is why you want to block IP, instead of deny all exept services you're runing.

Then, if you're afraid about some scanning, you can use an IDS that can detect many scan type and block such IP's.
This will we done automatically and what you will have to do is just checking thoses entries are corrects.

Regard's

 

by: kapotPosted on 2003-07-25 at 03:12:05ID: 9002888

vbadier,

I want to prevent SOME IPs accessing a SPECIFIC service :)

If I deny all, then how can I allow the rest ?

It's like a ban list I think.

Anyway, thanks for the help and discussion, it's really help !

 

by: KlintanPosted on 2003-07-25 at 10:12:40ID: 9006186

Take my fw example, then add as you need.

To accept incomming to webserver (http, httpS)

iptables -A INPUT -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j ACCEPT

To accept incomming ftp
iptables -A INPUT -p tcp --dport 21 -j ACCEPT

and so on...

Read this file if you need info on services
/etc/services

This link will help getting started with iptables
http://iptables-tutorial.frozentux.net/

20120131-EE-VQP-002

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