25 Most Frequently Used Linux IPTables Rules Examples

by RAMESH NATARAJAN on JUNE 14, 2011

At a first glance, IPTables rules might look cryptic.

In this article, I’ve given 25 practical IPTables rules that you can copy/paste and use it for your needs.

These examples will act as a basic templates for you to tweak these rules to suite your specific requirement.

For easy reference, all these 25 iptables rules are in shell script format: iptables-rules

1. Delete Existing Rules

Before you start building new set of rules, you might want to clean-up all the default rules, and existing rules. Use the iptables flush command as shown below to do this.

iptables -F
(or)
iptables --flush

2. Set Default Chain Policies

The default chain policy is ACCEPT. Change this to DROP for all INPUT, FORWARD, and OUTPUT chains as shown below.

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

When you make both INPUT, and OUTPUT chain’s default policy as DROP, for every firewall rule requirement you have, you should define two rules. i.e one for incoming and one for outgoing.

In all our examples below, we have two rules for each scenario, as we’ve set DROP as default policy for both INPUT and OUTPUT chain.

If you trust your internal users, you can omit the last line above. i.e Do not DROP all outgoing packets by default. In that case, for every firewall rule requirement you have, you just have to define only one rule. i.e define rule only for incoming, as the outgoing is ACCEPT for all packets.

Note: If you don’t know what a chain means, you should first familiarize yourself with the IPTables fundamentals.

3. Block a Specific ip-address

Before we proceed further will other examples, if you want to block a specific ip-address, you should do that first as shown below. Change the “x.x.x.x” in the following example to the specific ip-address that you like to block.

BLOCK_THIS_IP="x.x.x.x"
iptables -A INPUT -s "$BLOCK_THIS_IP" -j DROP

This is helpful when you find some strange activities from a specific ip-address in your log files, and you want to temporarily block that ip-address while you do further research.

You can also use one of the following variations, which blocks only TCP traffic on eth0 connection for this ip-address.

iptables -A INPUT -i eth0 -s "$BLOCK_THIS_IP" -j DROP
iptables -A INPUT -i eth0 -p tcp -s "$BLOCK_THIS_IP" -j DROP

4. Allow ALL Incoming SSH

The following rules allow ALL incoming ssh connections on eth0 interface.

iptables -A INPUT -i eth0 -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

Note: If you like to understand exactly what each and every one of the arguments means, you should read How to Add IPTables Firewall Rules

5. Allow Incoming SSH only from a Specific Network

The following rules allow incoming ssh connections only from 192.168.100.X network.

iptables -A INPUT -i eth0 -p tcp -s 192.168.100.0/24 --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

In the above example, instead of /24, you can also use the full subnet mask. i.e “192.168.100.0/255.255.255.0”.

6. Allow Incoming HTTP and HTTPS

The following rules allow all incoming web traffic. i.e HTTP traffic to port 80.

iptables -A INPUT -i eth0 -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT

The following rules allow all incoming secure web traffic. i.e HTTPS traffic to port 443.

iptables -A INPUT -i eth0 -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT

7. Combine Multiple Rules Together using MultiPorts

When you are allowing incoming connections from outside world to multiple ports, instead of writing individual rules for each and every port, you can combine them together using the multiport extension as shown below.

The following example allows all incoming SSH, HTTP and HTTPS traffic.

iptables -A INPUT -i eth0 -p tcp -m multiport --dports 22,80,443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp -m multiport --sports 22,80,443 -m state --state ESTABLISHED -j ACCEPT

8. Allow Outgoing SSH

The following rules allow outgoing ssh connection. i.e When you ssh from inside to an outside server.

iptables -A OUTPUT -o eth0 -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

Please note that this is slightly different than the incoming rule. i.e We allow both the NEW and ESTABLISHED state on the OUTPUT chain, and only ESTABLISHED state on the INPUT chain. For the incoming rule, it is vice versa.

9. Allow Outgoing SSH only to a Specific Network

The following rules allow outgoing ssh connection only to a specific network. i.e You an ssh only to 192.168.100.0/24 network from the inside.

iptables -A OUTPUT -o eth0 -p tcp -d 192.168.100.0/24 --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

10. Allow Outgoing HTTPS

The following rules allow outgoing secure web traffic. This is helpful when you want to allow internet traffic for your users. On servers, these rules are also helpful when you want to use wget to download some files from outside.

iptables -A OUTPUT -o eth0 -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT

Note: For outgoing HTTP web traffic, add two additional rules like the above, and change 443 to 80.

11. Load Balance Incoming Web Traffic

You can also load balance your incoming web traffic using iptables firewall rules.

This uses the iptables nth extension. The following example load balances the HTTPS traffic to three different ip-address. For every 3th packet, it is load balanced to the appropriate server (using the counter 0).

iptables -A PREROUTING -i eth0 -p tcp --dport 443 -m state --state NEW -m nth --counter 0 --every 3 --packet 0 -j DNAT --to-destination 192.168.1.101:443
iptables -A PREROUTING -i eth0 -p tcp --dport 443 -m state --state NEW -m nth --counter 0 --every 3 --packet 1 -j DNAT --to-destination 192.168.1.102:443
iptables -A PREROUTING -i eth0 -p tcp --dport 443 -m state --state NEW -m nth --counter 0 --every 3 --packet 2 -j DNAT --to-destination 192.168.1.103:443

12. Allow Ping from Outside to Inside

The following rules allow outside users to be able to ping your servers.

iptables -A INPUT -p icmp --icmp-type echo-request -j ACCEPT
iptables -A OUTPUT -p icmp --icmp-type echo-reply -j ACCEPT

13. Allow Ping from Inside to Outside

The following rules allow you to ping from inside to any of the outside servers.

iptables -A OUTPUT -p icmp --icmp-type echo-request -j ACCEPT
iptables -A INPUT -p icmp --icmp-type echo-reply -j ACCEPT

14. Allow Loopback Access

You should allow full loopback access on your servers. i.e access using 127.0.0.1

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

15. Allow Internal Network to External network.

On the firewall server where one ethernet card is connected to the external, and another ethernet card connected to the internal servers, use the following rules to allow internal network talk to external network.

In this example, eth1 is connected to external network (internet), and eth0 is connected to internal network (For example: 192.168.1.x).

iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT

16. Allow outbound DNS

The following rules allow outgoing DNS connections.

iptables -A OUTPUT -p udp -o eth0 --dport 53 -j ACCEPT
iptables -A INPUT -p udp -i eth0 --sport 53 -j ACCEPT

17. Allow NIS Connections

If you are running NIS to manage your user accounts, you should allow the NIS connections. Even when the SSH connection is allowed, if you don’t allow the NIS related ypbind connections, users will not be able to login.

The NIS ports are dynamic. i.e When the ypbind starts it allocates the ports.

First do a rpcinfo -p as shown below and get the port numbers. In this example, it was using port 853 and 850.

rpcinfo -p | grep ypbind

Now allow incoming connection to the port 111, and the ports that were used by ypbind.

iptables -A INPUT -p tcp --dport 111 -j ACCEPT
iptables -A INPUT -p udp --dport 111 -j ACCEPT
iptables -A INPUT -p tcp --dport 853 -j ACCEPT
iptables -A INPUT -p udp --dport 853 -j ACCEPT
iptables -A INPUT -p tcp --dport 850 -j ACCEPT
iptables -A INPUT -p udp --dport 850 -j ACCEPT

The above will not work when you restart the ypbind, as it will have different port numbers that time.

There are two solutions to this: 1) Use static ip-address for your NIS, or 2) Use some clever shell scripting techniques to automatically grab the dynamic port number from the “rpcinfo -p” command output, and use those in the above iptables rules.

18. Allow Rsync From a Specific Network

The following rules allows rsync only from a specific network.

iptables -A INPUT -i eth0 -p tcp -s 192.168.101.0/24 --dport 873 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 873 -m state --state ESTABLISHED -j ACCEPT

19. Allow MySQL connection only from a specific network

If you are running MySQL, typically you don’t want to allow direct connection from outside. In most cases, you might have web server running on the same server where the MySQL database runs.

However DBA and developers might need to login directly to the MySQL from their laptop and desktop using MySQL client. In those case, you might want to allow your internal network to talk to the MySQL directly as shown below.

iptables -A INPUT -i eth0 -p tcp -s 192.168.100.0/24 --dport 3306 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 3306 -m state --state ESTABLISHED -j ACCEPT

20. Allow Sendmail or Postfix Traffic

The following rules allow mail traffic. It may be sendmail or postfix.

iptables -A INPUT -i eth0 -p tcp --dport 25 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 25 -m state --state ESTABLISHED -j ACCEPT

21. Allow IMAP and IMAPS

The following rules allow IMAP/IMAP2 traffic.

iptables -A INPUT -i eth0 -p tcp --dport 143 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 143 -m state --state ESTABLISHED -j ACCEPT

The following rules allow IMAPS traffic.

iptables -A INPUT -i eth0 -p tcp --dport 993 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 993 -m state --state ESTABLISHED -j ACCEPT

22. Allow POP3 and POP3S

The following rules allow POP3 access.

iptables -A INPUT -i eth0 -p tcp --dport 110 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 110 -m state --state ESTABLISHED -j ACCEPT

The following rules allow POP3S access.

iptables -A INPUT -i eth0 -p tcp --dport 995 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 995 -m state --state ESTABLISHED -j ACCEPT

23. Prevent DoS Attack

The following iptables rule will help you prevent the Denial of Service (DoS) attack on your webserver.

iptables -A INPUT -p tcp --dport 80 -m limit --limit 25/minute --limit-burst 100 -j ACCEPT

In the above example:

  • -m limit: This uses the limit iptables extension
  • –limit 25/minute: This limits only maximum of 25 connection per minute. Change this value based on your specific requirement
  • –limit-burst 100: This value indicates that the limit/minute will be enforced only after the total number of connection have reached the limit-burst level.

24. Port Forwarding

The following example routes all traffic that comes to the port 442 to 22. This means that the incoming ssh connection can come from both port 22 and 422.

iptables -t nat -A PREROUTING -p tcp -d 192.168.102.37 --dport 422 -j DNAT --to 192.168.102.37:22

If you do the above, you also need to explicitly allow incoming connection on the port 422.

iptables -A INPUT -i eth0 -p tcp --dport 422 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 422 -m state --state ESTABLISHED -j ACCEPT

25. Log Dropped Packets

You might also want to log all the dropped packets. These rules should be at the bottom.

First, create a new chain called LOGGING.

iptables -N LOGGING

Next, make sure all the remaining incoming connections jump to the LOGGING chain as shown below.

iptables -A INPUT -j LOGGING

Next, log these packets by specifying a custom “log-prefix”.

iptables -A LOGGING -m limit --limit 2/min -j LOG --log-prefix "IPTables Packet Dropped: " --log-level 7

Finally, drop these packets.

iptables -A LOGGING -j DROP

All of the above 25 iptables rules are in shell script format: iptables-rules

Previous articles in the iptables series:

iptables 使用场景的更多相关文章

  1. Linux iptables:场景实战一

    <Linux iptables:规则原理和基础>和<Linux iptables:规则组成>介绍了iptables的基础及iptables规则的组成,本篇通过实际操作进行ipt ...

  2. iptables 配置场景3

    iptables -I INPUT -i lo -j ACCEPT    #允许本地回环地址访问: iptables -I INPUT -m state --state ESTABLISHED,REL ...

  3. iptables 配置 场景1

    这样配置完成后,没法完成本地回环,需要对lo网卡进行配置 本地报文无法发出,继续添加规则

  4. iptables的实战整理

    一.iptables使用场景:             内网情况下使用:在大并发的情况下不要开iptables否则影响性能 二.iptables出现下面的问题:             在yewufa ...

  5. iptables 学习

    本博客是学习慕课网课程 用iptables搭建一套强大的安全防护盾 整理而成 iptables相当于在ip层挂载一个hook point对用户进行控制 组成: 四张表+ 五条链(hook point) ...

  6. 腾讯云:iptables基础

    iptables 基础 iptables 基本命令 任务时间:5min ~ 10min iptables 可以简单理解为 Linux 系统内核级防火墙 netfilter 的用户态客户端. Linux ...

  7. linux基础简答(1)

    linux基础简答题 扇区及其4个主分区的原因 在第一个扇区中,保存着引导记录和分区信息,容量为512bytes,主引导记录(相当于MBR)446 bytes,分区表64bytes,记录每个分区信息要 ...

  8. Linux之安全应用

    一.关于iptables 定义:常见于linux系统下的应用层防火墙工具 二.Iptables规则原理和组成 1) Netfilter Netfilter是Linux操作系统核心层内部的一个数据包处理 ...

  9. Linux运维跳槽必备的40道面试精华题(转)

    Linux运维跳槽必备的40道面试精华题(转)   下面是一名资深Linux运维求职数十家公司总结的Linux运维面试精华,助力大家年后跳槽找个高薪好工作. 1.什么是运维?什么是游戏运维? 1)运维 ...

随机推荐

  1. 【HDU 2594 Simpsons' Hidden Talents】

    Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)Total Submission( ...

  2. Three Garlands~Educational Codeforces Round 35

    C. Three Garlands time limit per test 2 seconds memory limit per test 256 megabytes input standard i ...

  3. [1]区分event对象中的[clientX,offsetX,screenX,pageX]

    前言 在平时的开发中,非常讨厌的就是兼容性了,兼容性的问题总会让我们记忆混淆,所以这次来区分一下event对象中的常用获取鼠标位置. clientX clientY event.clientXeven ...

  4. VLC for iOS 2.3.0

    http://www.cocoachina.com/bbs/read.php?tid=231898 VLC for iOS 2.3.0       本帖属于CocoaChina会员发表,转帖请写明来源 ...

  5. undefined reference to XXX 问题原因

    原文地址:http://blog.csdn.net/cserchen/article/details/5503556 Linux下编译程序时,经常会遇到“undefined reference to ...

  6. Laravel向视图传递变量的两种方法

    //方法一 return view('home.user')->with('datas', $datas); //方法二 return view('home.user.my-indent',co ...

  7. NYOJ 71 乘船问题【贪心】

    时间复杂度O(n) 有n个人,第i个人的重量为w[i],每艘船的最大载重量均为c,且最多只能乘两个人.用最少的船装载所有人. 思路:从最轻的开始考虑,让最轻的和最重的一条船,若超出重量则可判定最重的只 ...

  8. UVA 1347 Tour 【双调旅行商/DP】

    John Doe, a skilled pilot, enjoys traveling. While on vacation, he rents a small plane and starts vi ...

  9. 基于django rest framework的mock server实践

    网上找了一下mock server的实现,发现python的基本都是基于flask来实现的,因最近在学django,就尝试用drf实现了下: A brief introduction of sui_m ...

  10. request与response对象.

    request与response对象. 1. request代表请求对象 response代表的响应对象. 学习它们我们可以操作http请求与响应. 2.request,response体系结构. 在 ...