Linux: 25 Iptables Netfilter Firewall Examples For New SysAdmins

Linux comes with a host based firewall called Netfilter. The netfilter is a set of hooks inside the Linux kernel that allows kernel modules to register callback functions with the network stack. A registered callback function is then called back for every packet that traverses the respective hook within the network stack. This Linux based firewall is controlled by the program called iptables to handles filtering for IPv4, and ip6tables handles filtering for IPv6. I strongly recommend that you first read our quick tutorial that explains how to configure a host-based firewall called Netfilter (iptables) under CentOS / RHEL / Fedora / Redhat Enterprise Linux. If you are using Ubuntu/Debian Linux, see how to setup UFW for more info. This post lists most simple iptables solutions required by a new Linux user to secure his or her Linux operating system from intruders.


This guide shows essential iptables command to control your daily life firewall rules and security of Linux server running on the bare metal server, router, or cloud server.

Linux Iptables Netfilter Firewall Examples For New SysAdmins

  • Most of the actions listed in this post written with the assumption that they will be executed by the root user running the bash or any other modern shell. Do not type commands on the remote system as it will disconnect your access.
  • For demonstration purpose, I’ve used RHEL 6.x, but the following command should work with any modern Linux distro that use the netfliter.
  • It is NOT a tutorial on how to set iptables. See tutorial here. It is a quick cheat sheet to common iptables commands.

1. Displaying the Status of Your Firewall

Type the following command as root:
# iptables -L -n -v
Sample outputs:

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination

Above output indicates that the firewall is not active. The following sample shows an active firewall:
# iptables -L -n -v
Sample outputs:

Chain INPUT (policy DROP 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
    0     0 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0           state INVALID
  394 43586 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
   93 17292 ACCEPT     all  --  br0    *       0.0.0.0/0            0.0.0.0/0
    1   142 ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0

Chain FORWARD (policy DROP 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
    0     0 ACCEPT     all  --  br0    br0     0.0.0.0/0            0.0.0.0/0
    0     0 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0           state INVALID
    0     0 TCPMSS     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp flags:0x06/0x02 TCPMSS clamp to PMTU
    0     0 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
    0     0 wanin      all  --  vlan2  *       0.0.0.0/0            0.0.0.0/0
    0     0 wanout     all  --  *      vlan2   0.0.0.0/0            0.0.0.0/0
    0     0 ACCEPT     all  --  br0    *       0.0.0.0/0            0.0.0.0/0

Chain OUTPUT (policy ACCEPT 425 packets, 113K bytes)
 pkts bytes target     prot opt in     out     source               destination

Chain wanin (1 references)
 pkts bytes target     prot opt in     out     source               destination

Chain wanout (1 references)
 pkts bytes target     prot opt in     out     source               destination

Where,

  • -L : List rules.
  • -v : Display detailed information. This option makes the list command show the interface name, the rule options, and the TOS masks. The packet and byte counters are also listed, with the suffix ‘K’, ‘M’ or ‘G’ for 1000, 1,000,000 and 1,000,000,000 multipliers respectively.
  • -n : Display IP address and port in numeric format. Do not use DNS to resolve names. This will speed up listing.

1.1. To inspect firewall with line numbers, enter:

# iptables -n -L -v --line-numbers
Sample outputs:

Chain INPUT (policy DROP)
num  target     prot opt source               destination
1    DROP       all  --  0.0.0.0/0            0.0.0.0/0           state INVALID
2    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
3    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0
4    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0

Chain FORWARD (policy DROP)
num  target     prot opt source               destination
1    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0
2    DROP       all  --  0.0.0.0/0            0.0.0.0/0           state INVALID
3    TCPMSS     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp flags:0x06/0x02 TCPMSS clamp to PMTU
4    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
5    wanin      all  --  0.0.0.0/0            0.0.0.0/0
6    wanout     all  --  0.0.0.0/0            0.0.0.0/0
7    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0

Chain OUTPUT (policy ACCEPT)
num  target     prot opt source               destination

Chain wanin (1 references)
num  target     prot opt source               destination

Chain wanout (1 references)
num  target     prot opt source               destination

You can use line numbers to delete or insert new rules into the firewall.

1.2. To display INPUT or OUTPUT chain rules, enter:

# iptables -L INPUT -n -v
# iptables -L OUTPUT -n -v --line-numbers

2. Stop / Start / Restart the Firewall

If you are using CentOS / RHEL / Fedora Linux, enter:
# service iptables stop
# service iptables start
# service iptables restart

You can use the iptables command itself to stop the firewall and delete all rules:
# iptables -F
# iptables -X
# iptables -t nat -F
# iptables -t nat -X
# iptables -t mangle -F
# iptables -t mangle -X
# iptables -P INPUT ACCEPT
# iptables -P OUTPUT ACCEPT
# iptables -P FORWARD ACCEPT

Where,

  • -F : Deleting (flushing) all the rules.
  • -X : Delete chain.
  • -t table_name : Select table (called nat or mangle) and delete/flush rules.
  • -P : Set the default policy (such as DROP, REJECT, or ACCEPT).

3. Delete Firewall Rules

To display line number along with other information for existing rules, enter:
# iptables -L INPUT -n --line-numbers
# iptables -L OUTPUT -n --line-numbers
# iptables -L OUTPUT -n --line-numbers | less
# iptables -L OUTPUT -n --line-numbers | grep 202.54.1.1

You will get the list of IP. Look at the number on the left, then use number to delete it. For example delete line number 4, enter:
# iptables -D INPUT 4
OR find source IP 202.54.1.1 and delete from rule:
# iptables -D INPUT -s 202.54.1.1 -j DROP
Where,

  • -D : Delete one or more rules from the selected chain

4. Insert Firewall Rules

To insert one or more rules in the selected chain as the given rule number use the following syntax. First find out line numbers, enter:
# iptables -L INPUT -n –line-numbers
Sample outputs:

Chain INPUT (policy DROP)
num  target     prot opt source               destination
1    DROP       all  --  202.54.1.1           0.0.0.0/0
2    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           state NEW,ESTABLISHED 

To insert rule between 1 and 2, enter:
# iptables -I INPUT 2 -s 202.54.1.2 -j DROP
To view updated rules, enter:
# iptables -L INPUT -n --line-numbers
Sample outputs:

Chain INPUT (policy DROP)
num  target     prot opt source               destination
1    DROP       all  --  202.54.1.1           0.0.0.0/0
2    DROP       all  --  202.54.1.2           0.0.0.0/0
3    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           state NEW,ESTABLISHED

5. Save Firewall Rules

To save firewall rules under CentOS / RHEL / Fedora Linux, enter:
# service iptables save
In this example, drop an IP and save firewall rules:
# iptables -A INPUT -s 202.5.4.1 -j DROP
# service iptables save

For all other distros use the iptables-save command:
# iptables-save > /root/my.active.firewall.rules
# cat /root/my.active.firewall.rules

6. Restore Firewall Rules

To restore firewall rules form a file called /root/my.active.firewall.rules, enter:
# iptables-restore
To restore firewall rules under CentOS / RHEL / Fedora Linux, enter:
# service iptables restart

7. Set the Default Firewall Policies

To drop all traffic:
# iptables -P INPUT DROP
# iptables -P OUTPUT DROP
# iptables -P FORWARD DROP
# iptables -L -v -n
#### you will not able to connect anywhere as all traffic is dropped ###
# ping cyberciti.biz
# wget http://www.kernel.org/pub/linux/kernel/v3.0/testing/linux-3.2-rc5.tar.bz2

7.1. Only Block Incoming Traffic

To drop all incoming / forwarded packets, but allow outgoing traffic, enter:
# iptables -P INPUT DROP
# iptables -P FORWARD DROP
# iptables -P OUTPUT ACCEPT
# iptables -A INPUT -m state --state NEW,ESTABLISHED -j ACCEPT
# iptables -L -v -n
### *** now ping and wget should work *** ###
# ping cyberciti.biz
# wget http://www.kernel.org/pub/linux/kernel/v3.0/testing/linux-3.2-rc5.tar.bz2

8. Drop Private Network Address On Public Interface

IP spoofing is nothing but to stop the following IPv4 address ranges for private networks on your public interfaces. Packets with non-routable source addresses should be rejected using the following syntax:
# iptables -A INPUT -i eth1 -s 192.168.0.0/24 -j DROP
# iptables -A INPUT -i eth1 -s 10.0.0.0/8 -j DROP

8.1. IPv4 Address Ranges For Private Networks (make sure you block them on public interface)

  • 10.0.0.0/8 -j (A)
  • 172.16.0.0/12 (B)
  • 192.168.0.0/16 (C)
  • 224.0.0.0/4 (MULTICAST D)
  • 240.0.0.0/5 (E)
  • 127.0.0.0/8 (LOOPBACK)

9. Blocking an IP Address (BLOCK IP)

To block an attackers ip address called 1.2.3.4, enter:
# iptables -A INPUT -s 1.2.3.4 -j DROP
# iptables -A INPUT -s 192.168.0.0/24 -j DROP

10. Block Incoming Port Requests (BLOCK PORT)

To block all service requests on port 80, enter:
# iptables -A INPUT -p tcp --dport 80 -j DROP
# iptables -A INPUT -i eth1 -p tcp --dport 80 -j DROP

To block port 80 only for an ip address 1.2.3.4, enter:
# iptables -A INPUT -p tcp -s 1.2.3.4 --dport 80 -j DROP
# iptables -A INPUT -i eth1 -p tcp -s 192.168.1.0/24 --dport 80 -j DROP

11. Block Outgoing IP Address

To block outgoing traffic to a particular host or domain such as cyberciti.biz, enter:
# host -t a cyberciti.biz
Sample outputs:

cyberciti.biz has address 75.126.153.206

Note down its ip address and type the following to block all outgoing traffic to 75.126.153.206:
# iptables -A OUTPUT -d 75.126.153.206 -j DROP
You can use a subnet as follows:
# iptables -A OUTPUT -d 192.168.1.0/24 -j DROP
# iptables -A OUTPUT -o eth1 -d 192.168.1.0/24 -j DROP

11.1. Example - Block Facebook.com Domain

First, find out all ip address of facebook.com, enter:
# host -t a www.facebook.com
Sample outputs:

www.facebook.com has address 69.171.228.40

Find CIDR for 69.171.228.40, enter:
# whois 69.171.228.40 | grep CIDR
Sample outputs:

CIDR:           69.171.224.0/19

To prevent outgoing access to www.facebook.com, enter:
# iptables -A OUTPUT -p tcp -d 69.171.224.0/19 -j DROP
You can also use domain name, enter:
# iptables -A OUTPUT -p tcp -d www.facebook.com -j DROP
# iptables -A OUTPUT -p tcp -d facebook.com -j DROP

From the iptables man page:

... specifying any name to be resolved with a remote query such as DNS (e.g., facebook.com is a really bad idea), a network IP address (with /mask), or a plain IP address ...

12. Log and Drop Packets

Type the following to log and block IP spoofing on public interface called eth1
# iptables -A INPUT -i eth1 -s 10.0.0.0/8 -j LOG --log-prefix "IP_SPOOF A: "
# iptables -A INPUT -i eth1 -s 10.0.0.0/8 -j DROP

By default everything is logged to /var/log/messages file.
# tail -f /var/log/messages
# grep --color 'IP SPOOF' /var/log/messages

13. Log and Drop Packets with Limited Number of Log Entries

The -m limit module can limit the number of log entries created per time. This is used to prevent flooding your log file. To log and drop spoofing per 5 minutes, in bursts of at most 7 entries .
# iptables -A INPUT -i eth1 -s 10.0.0.0/8 -m limit --limit 5/m --limit-burst 7 -j LOG --log-prefix "IP_SPOOF A: "
# iptables -A INPUT -i eth1 -s 10.0.0.0/8 -j DROP

14. Drop or Accept Traffic From Mac Address

Use the following syntax:
# iptables -A INPUT -m mac --mac-source 00:0F:EA:91:04:08 -j DROP
## *only accept traffic for TCP port # 8080 from mac 00:0F:EA:91:04:07 * ##
# iptables -A INPUT -p tcp --destination-port 22 -m mac --mac-source 00:0F:EA:91:04:07 -j ACCEPT

15. Block or Allow ICMP Ping Request

Type the following command to block ICMP ping requests:
# iptables -A INPUT -p icmp --icmp-type echo-request -j DROP
# iptables -A INPUT -i eth1 -p icmp --icmp-type echo-request -j DROP

Ping responses can also be limited to certain networks or hosts:
# iptables -A INPUT -s 192.168.1.0/24 -p icmp --icmp-type echo-request -j ACCEPT
The following only accepts limited type of ICMP requests:
### ** assumed that default INPUT policy set to DROP ** #############
iptables -A INPUT -p icmp --icmp-type echo-reply -j ACCEPT
iptables -A INPUT -p icmp --icmp-type destination-unreachable -j ACCEPT
iptables -A INPUT -p icmp --icmp-type time-exceeded -j ACCEPT
## ** all our server to respond to pings ** ##
iptables -A INPUT -p icmp --icmp-type echo-request -j ACCEPT

16. Open Range of Ports

Use the following syntax to open a range of ports:
iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 7000:7010 -j ACCEPT

17. Open Range of IP Addresses

Use the following syntax to open a range of IP address:
## only accept connection to tcp port 80 (Apache) if ip is between 192.168.1.100 and 192.168.1.200 ##
iptables -A INPUT -p tcp --destination-port 80 -m iprange --src-range 192.168.1.100-192.168.1.200 -j ACCEPT

## nat example ##
iptables -t nat -A POSTROUTING -j SNAT --to-source 192.168.1.20-192.168.1.25

18. Established Connections and Restarting The Firewall

When you restart the iptables service it will drop established connections as it unload modules from the system under RHEL / Fedora / CentOS Linux. Edit, /etc/sysconfig/iptables-config and set IPTABLES_MODULES_UNLOAD as follows:

IPTABLES_MODULES_UNLOAD = no

19. Help Iptables Flooding My Server Screen

Use the crit log level to send messages to a log file instead of console:
iptables -A INPUT -s 1.2.3.4 -p tcp --destination-port 80 -j LOG --log-level crit

20. Block or Open Common Ports

The following shows syntax for opening and closing common TCP and UDP ports:

Replace ACCEPT with DROP to block port:
## open port ssh tcp port 22 ##
iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 22 -j ACCEPT
 
## open cups (printing service) udp/tcp port 631 for LAN users ##
iptables -A INPUT -s 192.168.1.0/24 -p udp -m udp --dport 631 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -p tcp -m tcp --dport 631 -j ACCEPT
 
## allow time sync via NTP for lan users (open udp port 123) ##
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p udp --dport 123 -j ACCEPT
 
## open tcp port 25 (smtp) for all ##
iptables -A INPUT -m state --state NEW -p tcp --dport 25 -j ACCEPT
 
# open dns server ports for all ##
iptables -A INPUT -m state --state NEW -p udp --dport 53 -j ACCEPT
iptables -A INPUT -m state --state NEW -p tcp --dport 53 -j ACCEPT
 
## open http/https (Apache) server port to all ##
iptables -A INPUT -m state --state NEW -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -m state --state NEW -p tcp --dport 443 -j ACCEPT
 
## open tcp port 110 (pop3) for all ##
iptables -A INPUT -m state --state NEW -p tcp --dport 110 -j ACCEPT
 
## open tcp port 143 (imap) for all ##
iptables -A INPUT -m state --state NEW -p tcp --dport 143 -j ACCEPT
 
## open access to Samba file server for lan users only ##
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 137 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 138 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 139 -j ACCEPT
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 445 -j ACCEPT
 
## open access to proxy server for lan users only ##
iptables -A INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 3128 -j ACCEPT
 
## open access to mysql server for lan users only ##
iptables -I INPUT -p tcp --dport 3306 -j ACCEPT

21. Restrict the Number of Parallel Connections To a Server Per Client IP

You can use connlimit module to put such restrictions. To allow 3 ssh connections per client host, enter:
# iptables -A INPUT -p tcp --syn --dport 22 -m connlimit --connlimit-above 3 -j REJECT

Set HTTP requests to 20:
# iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above 20 --connlimit-mask 24 -j DROP
Where,

  1. --connlimit-above 3 : Match if the number of existing connections is above 3.
  2. --connlimit-mask 24 : Group hosts using the prefix length. For IPv4, this must be a number between (including) 0 and 32.

22. List NAT rules

The syntax is
# iptables -t nat -L -n -v
Sample outputs:

Chain PREROUTING (policy ACCEPT 496K packets, 29M bytes)
 pkts bytes target     prot opt in     out     source               destination         
43557 2613K DNAT       tcp  --  *      *       0.0.0.0/0            192.168.184.8        tcp dpt:443 to:10.105.28.42:443
68700 4122K DNAT       tcp  --  *      *       0.0.0.0/0            192.168.184.8        tcp dpt:80 to:10.105.28.42:80
15855  951K DNAT       tcp  --  *      *       0.0.0.0/0            192.168.184.8        tcp dpt:444 to:10.105.28.45:444
16009  961K DNAT       tcp  --  *      *       0.0.0.0/0            192.168.184.8        tcp dpt:81 to:10.105.28.45:81
63495 3810K DNAT       tcp  --  *      *       0.0.0.0/0            192.168.184.8        tcp dpt:445 to:10.105.28.44:445
19615 1177K DNAT       tcp  --  *      *       0.0.0.0/0            192.168.184.8        tcp dpt:82 to:10.105.28.44:82
 
Chain INPUT (policy ACCEPT 488K packets, 29M bytes)
 pkts bytes target     prot opt in     out     source               destination         
 
Chain OUTPUT (policy ACCEPT 3280 packets, 207K bytes)
 pkts bytes target     prot opt in     out     source               destination         
 
Chain POSTROUTING (policy ACCEPT 231K packets, 14M bytes)
 pkts bytes target     prot opt in     out     source               destination         
 3832  230K MASQUERADE  all  --  *      *       10.105.28.0/24      !10.105.28.0/24       /* generated for LXD network lxdbr0 */

Another option:
# iptables -t nat -v -L -n --line-number

23. Delete NAT rules

The syntax is as follows to list NAT rules on Linux:
# iptables -t nat -v -L -n --line-number
# iptables -t nat -v -L PREROUTING -n --line-number
# iptables -t nat -v -L POSTROUTING -n --line-number

To delete PREROUTING rule, run:
# iptables -t nat -D PREROUTING {number-here}
# iptables -t nat -D PREROUTING 42

To delete POSTROUTING rule, run:
# iptables -t nat -D POSTROUTING {number-here}
# iptables -t nat -D POSTROUTING 42

24. How to redirect port AA to BB

The syntax is as follows:
iptables -t nat -A PREROUTING -i $interfaceName -p tcp --dport $srcPortNumber -j REDIRECT --to-port $dstPortNumber
To redirect all incoming traffic on port 80 redirect to port 8080
# iptables -t nat -I PREROUTING --src 0/0 --dst 192.168.1.5 -p tcp --dport 80 -j REDIRECT --to-ports 8080

25. How to reset packet counters

To see iptables counters run:
# iptables -L -n -v
To clear/reset the counters for all rules:
# iptables -Z
# iptables -L -n -v

To reset the counters for INPUT chain only:
# iptables -Z INPUT
To reset the counters for rule # 13 in the INPUT chain only:
# iptables -Z INPUT 13

26. HowTO: Use iptables Like a Pro

For more information about iptables, please see the manual page by typing man iptables from the command line:
$ man iptables
You can see the help using the following syntax too:
# iptables -h
To see help with specific commands and targets, enter:
# iptables -j DROP -h

27. Testing Your Firewall

Find out if ports are open or not, enter:
# netstat -tulpn
Find out if tcp port 80 open or not, enter:
# netstat -tulpn | grep :80
If port 80 is not open, start the Apache, enter:
# service httpd start
Make sure iptables allowing access to the port 80:
# iptables -L INPUT -v -n | grep 80
Otherwise open port 80 using the iptables for all users:
# iptables -A INPUT -m state --state NEW -p tcp --dport 80 -j ACCEPT
# service iptables save

Use the telnet command to see if firewall allows to connect to port 80:
$ telnet www.cyberciti.biz 80
Sample outputs:

Trying 75.126.153.206...
Connected to www.cyberciti.biz.
Escape character is '^]'.
^]

telnet> quit
Connection closed.

You can use the nmap command to probe your own server using the following syntax:
$ nmap -sS -p 80 www.cyberciti.biz
Sample outputs:

Starting Nmap 5.00 ( http://nmap.org ) at 2011-12-13 13:19 IST
Interesting ports on www.cyberciti.biz (75.126.153.206):
PORT   STATE SERVICE
80/tcp open  http

Nmap done: 1 IP address (1 host up) scanned in 1.00 seconds

I also recommend you install and use sniffer such as tcpdupm and ngrep to test your firewall settings.

Conclusion:

This post only list basic rules for new Linux users. You can create and build more complex rules. This requires good understanding of TCP/IP, Linux kernel tuning via sysctl.conf, and good knowledge of your own setup. Stay tuned for next topics:

  • Stateful packet inspection.
  • Using connection tracking helpers.
  • Network address translation.
  • Layer 2 filtering.
  • Firewall testing tools.
  • Dealing with VPNs, DNS, Web, Proxy, and other protocols.
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82 comments… add one
  • Awesome Nov 3, 2020 @ 7:07

    Awesome and was very helpful to me.

  • Mandar Jun 9, 2017 @ 7:36

    Hii All,
    Can any one help me for security.
    I want to accept traffic over UDP from particular MAC or device

  • ben Jan 29, 2017 @ 21:30

    can someone put all the recommend lines in one file?
    i see the comments here , and i didn’t get it what to put

  • Paran Jan 5, 2017 @ 17:27

    Thanks to all, really this site is excellent to gather knowledge.
    Right now my boss has assigned me a new task. I would like to share this also need to solve the problem. Please help me.
    How to blocked an IP address which is request in my server port (Tomcat) more or equal twenty times per second.
    Suppose my server ip is 123.123.123.123 with it’s port is 80. However, another IP address is concurrently requested in my server. IP address may be different. But, it can be identified by their nature. Per second can attack in my server more that 20 times.

  • DECPNQ Aug 23, 2016 @ 15:41

    Wow. Awesome examples. I loved it. Thanks!!!!!!!!!!!

  • Chống Trá»™m Quảng Ngãi Apr 30, 2016 @ 3:36

    CSF firewall base on iptables is very good for me. I think new SysAdmins should using CSF firewall.

  • davidrom Apr 29, 2016 @ 9:06

    you just have to make sure they’re in the correct order. #18: Established Connections and >>>Restaring<<< The Linux Firewall

  • Imran Khan Feb 7, 2016 @ 11:59

    Hello Team,

    Gr8 Iptables notes. Will try & share if found any discripency on command.

    Thanks,

  • Priscila Dec 14, 2015 @ 4:11

    The reason why so many poplee use VIM is because it is a text editor that you can use right in the command line and it has so many powerful features. People find that once they get used to using VIM that it is

  • Ramesh Das Apr 6, 2015 @ 19:32

    iptables -p tcp –syn –dport 80 -m connlimit –connlimit-above 20 –connlimit-mask 24 -j DROP

    I tried above but its not taking through so if am not wrong then it should be as below.

    iptables -A INPUT -p tcp –syn –dport 80 -m connlimit –connlimit-above 20 –connlimit-mask 24 -j DROP

  • Ron Barak Dec 1, 2014 @ 16:44

    Useful page.
    Here’s errtum I found
    #18: Established Connections and >>>Restaring<<< The Firewall

  • Ron Barak Dec 1, 2014 @ 16:43

    Useful page.
    Here’XXX errXXX I found
    #18: Established Connections and >>>Restaring<<< The Firewall

  • Bas Oct 15, 2014 @ 17:52

    Nice breakdown on iptables!

    However, I prefer (& recommend) to use a firewall manager (command-line / config file based tool) like shorewall:

    http://shorewall.net/

  • Darko Vrsic Oct 15, 2014 @ 9:30

    Very nice!

    Thank you!

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