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IPTABLES — Rules and Commands

Maciej
8 min readMar 4, 2019

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Saving Rules

  • Debian Based
netfilter-persistent save
  • RedHat
service iptables save

List out all of the active iptables rules with verbose

iptables -n -L -v

List out all of the active iptables rules with numeric lines and verbose

iptables -n -L -v --line-numbers

Print out all of the active iptables rules

iptables -S

List Rules as Tables for INPUT chain

iptables -L INPUT

Print all of the rule specifications in the INPUT chain

iptables -S INPUT

Show Packet Counts and Aggregate Size

iptables -L INPUT -v

To display INPUT or OUTPUT chain rules with numeric lines and verbose

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

Delete Rule by Chain and Number

iptables -D INPUT 10

Delete Rule by Specification

iptables -D INPUT -m conntrack --ctstate INVALID -j DROP

Flush All Rules, Delete All Chains, and Accept All

iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPTiptables -t nat -F
iptables -t mangle -F
iptables -F
iptables -X

Flush All Chains

iptables -F

Flush a Single Chain

iptables -F INPUT

Insert Firewall Rules

iptables -I INPUT 2 -s 192.168.1.2 -j DROP

Allow Loopback Connections

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

Allow Established and Related Incoming Connections

iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT

Allow Established Outgoing Connections

iptables -A OUTPUT -m conntrack --ctstate ESTABLISHED -j ACCEPT

Internal to External

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

Drop Invalid Packets

iptables -A INPUT -m conntrack --ctstate INVALID -j DROP

Block an IP Address

iptables -A INPUT -s 192.168.252.12 -j DROP

Block and IP Address and Reject

iptables -A INPUT -s 192.168.252.12 -j REJECT

Block Connections to a Network Interface

iptables -A INPUT -i eth0 -s 192.168.252.12 -j DROP

Allow All Incoming SSH

iptables -A INPUT -p tcp --dport 22 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --sport 22 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow Incoming SSH from Specific IP address or subnet

iptables -A INPUT -p tcp -s 192.168.240.0/24 --dport 22 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --sport 22 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow Outgoing SSH

iptables -A OUTPUT -p tcp --dport 22 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p tcp --sport 22 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow Incoming Rsync from Specific IP Address or Subnet

iptables -A INPUT -p tcp -s 192.168.240.0/24 --dport 873 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --sport 873 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow All Incoming HTTP

iptables -A INPUT -p tcp --dport 80 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --sport 80 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow All Incoming HTTPS

iptables -A INPUT -p tcp --dport 443 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --sport 443 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow All Incoming HTTP and HTTPS

iptables -A INPUT -p tcp -m multiport --dports 80,443 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -m multiport --dports 80,443 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow MySQL from Specific IP Address/Subnet

iptables -A INPUT -p tcp -s 192.168.240.0/24 --dport 3306 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --sport 3306 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow MySQL to Specific Network Interface

iptables -A INPUT -i eth1 -p tcp --dport 3306 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth1 -p tcp --sport 3306 -m conntrack --ctstate ESTABLISHED -j ACCEPT

PostgreSQL from Specific IP Address/Subnet

iptables -A INPUT -p tcp -s 192.168.240.0/24 --dport 5432 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --sport 5432 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow PostgreSQL to Specific Network Interface

iptables -A INPUT -i eth1 -p tcp --dport 5432 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth1 -p tcp --sport 5432 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Block Outgoing SMTP Mail

iptables -A OUTPUT -p tcp --dport 25 -j REJECT

Allow All Incoming SMTP

iptables -A INPUT -p tcp --dport 25 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --sport 25 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow All Incoming IMAP

iptables -A INPUT -p tcp --dport 143 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --sport 143 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow All Incoming IMAP

iptables -A INPUT -p tcp --dport 993 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --sport 993 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow All Incoming POP3

iptables -A INPUT -p tcp --dport 110 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --sport 110 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Allow All Incoming POP3S

iptables -A INPUT -p tcp --dport 995 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --sport 995 -m conntrack --ctstate ESTABLISHED -j ACCEPT

Drop Private Network Address On Public Interface

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

Log and Drop Packets

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

Log and Drop Packets with Limited Number of Log 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

Drop or Accept Traffic From Mac Address

iptables -A INPUT -m mac --mac-source 00:0F:EA:91:04:08 -j DROP
iptables -A INPUT -p tcp --destination-port 22 -m mac --mac-source 00:0F:EA:91:04:07 -j ACCEPT

Block or Allow ICMP Ping Request

iptables -A INPUT -p icmp --icmp-type echo-request -j DROP
iptables -A INPUT -i eth1 -p icmp --icmp-type echo-request -j DROP

Specifying Multiple Ports with multiport

iptables -A INPUT -i eth0 -p tcp -m state --state NEW -m multiport --dports ssh,smtp,http,https -j ACCEPT

Restricting the Number of Connections with limit and iplimit

iptables -A FORWARD -m state --state NEW -p tcp -m multiport --dport http,https -o eth0 -i eth1 -m limit --limit 20/hour --limit-burst 5 -j ACCEPT

or

iptables -A INPUT -p tcp -m state --state NEW --dport http -m iplimit --iplimit-above 5 -j DROP

Maintaining a List of recent Connections to Match Against

iptables -A FORWARD -m recent --name portscan --rcheck --seconds 100 -j DROP
iptables -A FORWARD -p tcp -i eth0 --dport 443 -m recent --name portscan --set -j DROP

Matching Against a string* in a Packet's Data Payload

iptables -A FORWARD -m string --string '.com' -j DROP
iptables -A FORWARD -m string --string '.exe' -j DROP

Time-based Rules with time*

iptables -A FORWARD -p tcp -m multiport --dport http,https -o eth0 -i eth1 \
    -m time --timestart 21:30 --timestop 22:30 --days Mon,Tue,Wed,Thu,Fri -j ACCEPT

Packet Matching Based on TTL Values

iptables -A INPUT -s 1.2.3.4 -m ttl --ttl-lt 40 -j REJECT

Protection against port scanning

iptables -N port-scanning
iptables -A port-scanning -p tcp --tcp-flags SYN,ACK,FIN,RST RST -m limit --limit 1/s --limit-burst 2 -j RETURN
iptables -A port-scanning -j DROP

SSH brute-force protection

iptables -A INPUT -p tcp --dport ssh -m conntrack --ctstate NEW -m recent --set
iptables -A INPUT -p tcp --dport ssh -m conntrack --ctstate NEW -m recent --update --seconds 60 --hitcount 10 -j DROP

Syn-flood protection

iptables -N syn_floodiptables -A INPUT -p tcp --syn -j syn_flood
iptables -A syn_flood -m limit --limit 1/s --limit-burst 3 -j RETURN
iptables -A syn_flood -j DROPiptables -A INPUT -p icmp -m limit --limit  1/s --limit-burst 1 -j ACCEPTiptables -A INPUT -p icmp -m limit --limit 1/s --limit-burst 1 -j LOG --log-prefix PING-DROP:
iptables -A INPUT -p icmp -j DROPiptables -A OUTPUT -p icmp -j ACCEPT

Mitigating SYN Floods With SYNPROXY

iptables -t raw -A PREROUTING -p tcp -m tcp --syn -j CT --notrack
iptables -A INPUT -p tcp -m tcp -m conntrack --ctstate INVALID,UNTRACKED -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460
iptables -A INPUT -m conntrack --ctstate INVALID -j DROP

Block New Packets That Are Not SYN

iptables -A INPUT -p tcp ! --syn -m state --state NEW -j DROP

or

iptables -t mangle -A PREROUTING -p tcp ! --syn -m conntrack --ctstate NEW -j DROP

Force Fragments packets check

iptables -A INPUT -f -j DROP

XMAS packets

iptables -A INPUT -p tcp --tcp-flags ALL ALL -j DROP

Drop all NULL packets

iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP

Block Uncommon MSS Values

iptables -t mangle -A PREROUTING -p tcp -m conntrack --ctstate NEW -m tcpmss ! --mss 536:65535 -j DROP

Block Packets With Bogus TCP Flags

iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,SYN FIN,SYN -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags SYN,RST SYN,RST -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,RST FIN,RST -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags FIN,ACK FIN -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ACK,URG URG -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ACK,FIN FIN -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ACK,PSH PSH -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ALL ALL -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ALL NONE -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ALL FIN,PSH,URG -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ALL SYN,FIN,PSH,URG -j DROP
iptables -t mangle -A PREROUTING -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP

Block Packets From Private Subnets Spoof

_subnets=("224.0.0.0/3" "169.254.0.0/16" "172.16.0.0/12" "192.0.2.0/24" "192.168.0.0/16" "10.0.0.0/8" "0.0.0.0/8" "240.0.0.0/5")for _sub in "${_subnets[@]}" ; do
  iptables -t mangle -A PREROUTING -s "$_sub" -j DROP
done
iptables -t mangle -A PREROUTING -s 127.0.0.0/8 ! -i lo -j DROP

Tools:

Shoreline Firewall (Shorewall)

The Shorewall Logo is the work of Gareth Davies of Thusa and is licensed under the Creative Commons Attribution-Share…

shorewall.org

Home

Welcome to the firewalld project homepage! Firewalld provides a dynamically managed firewall with support for…

firewalld.org

UncomplicatedFirewall - Ubuntu Wiki

The Linux kernel in Ubuntu provides a packet filtering system called netfilter, and the traditional interface for…

wiki.ubuntu.com

firehol/firehol

A firewall for humans... Contribute to firehol/firehol development by creating an account on GitHub.

github.com

Tutorials:

Best practices: iptables

Anyone who has used iptables before has locked themselves out of a remote server at least once. It's easily avoided…

major.io

Best practices: iptables

Anyone who has used iptables before has locked themselves out of a remote server at least once. It's easily avoided…

major.io

Debugging iptables and common firewall pitfalls?

Viewing and modifying the firewall configuration requires administrator privileges ( root) as does opening services in…

serverfault.com

Quick HOWTO : Ch14 : Linux Firewalls Using iptables

Network security is a primary consideration in any decision to host a website as the threats are becoming more…

www.linuxhomenetworking.com

Linux netfilter Hacking HOWTO: Information for Programmers

Next Previous Contents I'll let you in on a secret: my pet hamster did all the coding. I was just a channel, a `front'…

www.netfilter.org

Per-IP rate limiting with iptables

Every second, Pusher's main pub-sub system handles 9,000 new WebSocket connections. No sweat. But earlier this year…

making.pusher.com

Networking
Firewall
Linux
Iptables
Tutorial

 by the author.

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Maciej

Written by Maciej

766 Followers

DevOps Consultant. I’m strongly focused on automation, security, and reliability.

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