Iptables Essentials: Common Firewall Rules and Commands


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Created by trimstray and contributors

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## :ballot_box_with_check: Todo - [ ] Add useful Iptables configuration examples - [ ] Add useful Kernel Settings (sysctl) configuration examples - [ ] Add links to useful external resources - [ ] Add advanced configuration examples, commands, rules **** ## Table Of Content - [Tools to help you configure Iptables](#tools-to-help-you-configure-iptables) - [Manuals/Howtos/Tutorials](#manualshowtostutorials) - [How it works?](#how-it-works) - [Iptables Rules](#iptables-rules) * [Saving Rules](#saving-rules) - [Debian Based](#debian-based) - [RedHat Based](#redhat-based) * [List out all of the active iptables rules with verbose](#list-out-all-of-the-active-iptables-rules-with-verbose) * [List out all of the active iptables rules with numeric lines and verbose](#list-out-all-of-the-active-iptables-rules-with-numeric-lines-and-verbose) * [Print out all of the active iptables rules](#print-out-all-of-the-active-iptables-rules) * [List Rules as Tables for INPUT chain](#list-rules-as-tables-for-input-chain) * [Print all of the rule specifications in the INPUT chain](#print-all-of-the-rule-specifications-in-the-input-chain) * [Show Packet Counts and Aggregate Size](#show-packet-counts-and-aggregate-size) * [To display INPUT or OUTPUT chain rules with numeric lines and verbose](#to-display-input-or-output-chain-rules-with-numeric-lines-and-verbose) * [Delete Rule by Chain and Number](#delete-rule-by-chain-and-number) * [Delete Rule by Specification](#delete-rule-by-specification) * [Flush All Rules, Delete All Chains, and Accept All](#flush-all-rules--delete-all-chains--and-accept-all) * [Flush All Chains](#flush-all-chains) * [Flush a Single Chain](#flush-a-single-chain) * [Insert Firewall Rules](#insert-firewall-rules) * [Allow Loopback Connections](#allow-loopback-connections) * [Allow Established and Related Incoming Connections](#allow-established-and-related-incoming-connections) * [Allow Established Outgoing Connections](#allow-established-outgoing-connections) * [Internal to External](#internal-to-external) * [Drop Invalid Packets](#drop-invalid-packets) * [Block an IP Address](#block-an-ip-address) * [Block and IP Address and Reject](#block-and-ip-address-and-reject) * [Block Connections to a Network Interface](#block-connections-to-a-network-interface-1) * [Allow All Incoming SSH](#allow-all-incoming-ssh) * [Allow Incoming SSH from Specific IP address or subnet](#allow-incoming-ssh-from-specific-ip-address-or-subnet) * [Allow Outgoing SSH](#allow-outgoing-ssh) * [Allow Incoming Rsync from Specific IP Address or Subnet](#allow-incoming-rsync-from-specific-ip-address-or-subnet) * [Allow All Incoming HTTP](#allow-all-incoming-http) * [Allow All Incoming HTTPS](#allow-all-incoming-https) * [Allow All Incoming HTTP and HTTPS](#allow-all-incoming-http-and-https) * [Allow MySQL from Specific IP Address or Subnet](#allow-mysql-from-specific-ip-address-or-subnet) * [Allow MySQL to Specific Network Interface](#allow-mysql-to-specific-network-interface) * [PostgreSQL from Specific IP Address or Subnet](#postgresql-from-specific-ip-address-or-subnet) * [Allow PostgreSQL to Specific Network Interface](#allow-postgresql-to-specific-network-interface) * [Block Outgoing SMTP Mail](#block-outgoing-smtp-mail) * [Allow All Incoming SMTP](#allow-all-incoming-smtp) * [Allow All Incoming IMAP](#allow-all-incoming-imap) * [Allow All Incoming IMAPS](#allow-all-incoming-imaps) * [Allow All Incoming POP3](#allow-all-incoming-pop3) * [Allow All Incoming POP3S](#allow-all-incoming-pop3s) * [Drop Private Network Address On Public Interface](#drop-private-network-address-on-public-interface) * [Drop All Outgoing to Facebook Networks](#drop-all-outgoing-to-facebook-networks) * [Log and Drop Packets](#log-and-drop-packets) * [Log and Drop Packets with Limited Number of Log Entries](#log-and-drop-packets-with-limited-number-of-log-entries) * [Drop or Accept Traffic From Mac Address](#drop-or-accept-traffic-from-mac-address) * [Block or Allow ICMP Ping Request](#block-or-allow-icmp-ping-request) * [Specifying Multiple Ports with `multiport`](#specifying-multiple-ports-with--multiport-) * [Load Balancing with `random*` or `nth*`](#load-balancing-with--random---or--nth--) * [Restricting the Number of Connections with `limit` and `iplimit*`](#restricting-the-number-of-connections-with--limit--and--iplimit--) * [Maintaining a List of recent Connections to Match Against](#maintaining-a-list-of-recent-connections-to-match-against) * [Matching Against a `string*` in a Packet's Data Payload](#matching-against-a--string---in-a-packet-s-data-payload) * [Time-based Rules with `time*`](#time-based-rules-with--time--) * [Packet Matching Based on TTL Values](#packet-matching-based-on-ttl-values) * [Protection against port scanning](#protection-against-port-scanning) * [SSH brute-force protection](#ssh-brute-force-protection) * [Syn-flood protection](#syn-flood-protection) + [Mitigating SYN Floods With SYNPROXY](#mitigating-syn-floods-with-synproxy) * [Block New Packets That Are Not SYN](#block-new-packets-that-are-not-syn) * [Force Fragments packets check](#force-fragments-packets-check) * [XMAS packets](#xmas-packets) * [Drop all NULL packets](#drop-all-null-packets) * [Block Uncommon MSS Values](#block-uncommon-mss-values) * [Block Packets With Bogus TCP Flags](#block-packets-with-bogus-tcp-flags) * [Block Packets From Private Subnets (Spoofing)](#block-packets-from-private-subnets--spoofing-) **** ### Tools to help you configure Iptables

  :small_orange_diamond: Shorewall - advanced gateway/firewall configuration tool for GNU/Linux.
  :small_orange_diamond: Firewalld - provides a dynamically managed firewall.
  :small_orange_diamond: UFW - default firewall configuration tool for Ubuntu.
  :small_orange_diamond: FireHOL - offer simple and powerful configuration for all Linux firewall and traffic shaping requirements.

### Manuals/Howtos/Tutorials

  :small_orange_diamond: Best practices: iptables - by Major Hayden
  :small_orange_diamond: An In-Depth Guide to Iptables, the Linux Firewall
  :small_orange_diamond: Advanced Features of netfilter/iptables
  :small_orange_diamond: Linux Firewalls Using iptables
  :small_orange_diamond: Debugging iptables and common firewall pitfalls?
  :small_orange_diamond: Netfilter Hacking HOWTO
  :small_orange_diamond: Per-IP rate limiting with iptables

### How it works?

Master

### Iptables Rules #### Saving Rules ###### Debian Based ```bash netfilter-persistent save ``` ###### RedHat Based ```bash service iptables save ``` #### List out all of the active iptables rules with verbose ```bash iptables -n -L -v ``` #### List out all of the active iptables rules with numeric lines and verbose ```bash iptables -n -L -v --line-numbers ``` #### Print out all of the active iptables rules ```bash iptables -S ``` #### List Rules as Tables for INPUT chain ```bash iptables -L INPUT ``` #### Print all of the rule specifications in the INPUT chain ```bash iptables -S INPUT ``` #### Show Packet Counts and Aggregate Size ```bash iptables -L INPUT -v ``` #### To display INPUT or OUTPUT chain rules with numeric lines and verbose ```bash iptables -L INPUT -n -v iptables -L OUTPUT -n -v --line-numbers ``` #### Delete Rule by Chain and Number ```bash iptables -D INPUT 10 ``` #### Delete Rule by Specification ```bash iptables -D INPUT -m conntrack --ctstate INVALID -j DROP ``` #### Flush All Rules, Delete All Chains, and Accept All ```bash iptables -P INPUT ACCEPT iptables -P FORWARD ACCEPT iptables -P OUTPUT ACCEPT iptables -t nat -F iptables -t mangle -F iptables -F iptables -X ``` #### Flush All Chains ```bash iptables -F ``` #### Flush a Single Chain ```bash iptables -F INPUT ``` #### Insert Firewall Rules ```bash iptables -I INPUT 2 -s 202.54.1.2 -j DROP ``` #### Allow Loopback Connections ```bash iptables -A INPUT -i lo -j ACCEPT iptables -A OUTPUT -o lo -j ACCEPT ``` #### Allow Established and Related Incoming Connections ```bash iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT ``` #### Allow Established Outgoing Connections ```bash iptables -A OUTPUT -m conntrack --ctstate ESTABLISHED -j ACCEPT ``` #### Internal to External ```bash iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT ``` #### Drop Invalid Packets ```bash iptables -A INPUT -m conntrack --ctstate INVALID -j DROP ``` #### Block an IP Address ```bash iptables -A INPUT -s 192.168.252.10 -j DROP ``` #### Block and IP Address and Reject ```bash iptables -A INPUT -s 192.168.252.10 -j REJECT ``` #### Block Connections to a Network Interface ```bash iptables -A INPUT -i eth0 -s 192.168.252.10 -j DROP ``` #### Allow All Incoming SSH ```bash 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 ```bash 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 ```bash 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 ```bash 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 ```bash 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 ```bash 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 ```bash 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 or Subnet ```bash 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 ```bash 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 or Subnet ```bash 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 ```bash 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 ```bash iptables -A OUTPUT -p tcp --dport 25 -j REJECT ``` #### Allow All Incoming SMTP ```bash 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 ```bash 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 IMAPS ```bash 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 ```bash 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 ```bash 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 ```bash 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 ``` #### Drop All Outgoing to Facebook Networks Get Facebook AS: ```bash whois -h v4.whois.cymru.com " -v $(host facebook.com | grep "has address" | cut -d " " -f4)" | tail -n1 | awk '{print $1}' ``` Drop: ```bash for i in $(whois -h whois.radb.net -- '-i origin AS32934' | grep "^route:" | cut -d ":" -f2 | sed -e 's/^[ \t]*//' | sort -n -t . -k 1,1 -k 2,2 -k 3,3 -k 4,4 | cut -d ":" -f2 | sed 's/$/;/') ; do iptables -A OUTPUT -s "$i" -j REJECT done ``` #### Log and Drop Packets ```bash iptables -A INPUT -i eth1 -s 10.0.0.0/8 -j LOG --log-prefix "IP_SPOOF A: " iptables -A INPUT -i eth1 -s 10.0.0.0/8 -j DROP ``` By default everything is logged to `/var/log/messages` file: ```bash tail -f /var/log/messages grep --color 'IP SPOOF' /var/log/messages ``` #### Log and Drop Packets with Limited Number of Log Entries ```bash iptables -A INPUT -i eth1 -s 10.0.0.0/8 -m limit --limit 5/m --limit-burst 7 -j LOG --log-prefix "IP_SPOOF A: " iptables -A INPUT -i eth1 -s 10.0.0.0/8 -j DROP ``` #### Drop or Accept Traffic From Mac Address ```bash iptables -A INPUT -m mac --mac-source 00:0F:EA:91:04:08 -j DROP iptables -A INPUT -p tcp --destination-port 22 -m mac --mac-source 00:0F:EA:91:04:07 -j ACCEPT ``` #### Block or Allow ICMP Ping Request ```bash iptables -A INPUT -p icmp --icmp-type echo-request -j DROP iptables -A INPUT -i eth1 -p icmp --icmp-type echo-request -j DROP ``` #### Specifying Multiple Ports with `multiport` ```bash iptables -A INPUT -i eth0 -p tcp -m state --state NEW -m multiport --dports ssh,smtp,http,https -j ACCEPT ``` #### Load Balancing with `random*` or `nth*` ```bash _ips=("172.31.250.10" "172.31.250.11" "172.31.250.12" "172.31.250.13") for ip in "${_ips[@]}" ; do iptables -A PREROUTING -i eth0 -p tcp --dport 80 -m state --state NEW -m nth --counter 0 --every 4 --packet 0 \ -j DNAT --to-destination ${ip}:80 done ``` or ```bash _ips=("172.31.250.10" "172.31.250.11" "172.31.250.12" "172.31.250.13") for ip in "${_ips[@]}" ; do iptables -A PREROUTING -i eth0 -p tcp --dport 80 -m state --state NEW -m random --average 25 \ -j DNAT --to-destination ${ip}:80 done ``` #### Restricting the Number of Connections with `limit` and `iplimit*` ```bash 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 ```bash 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 ```bash 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 ```bash iptables -A FORWARD -m string --string '.com' -j DROP iptables -A FORWARD -m string --string '.exe' -j DROP ``` #### Time-based Rules with `time*` ```bash 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 ```bash iptables -A INPUT -s 1.2.3.4 -m ttl --ttl-lt 40 -j REJECT ``` #### Protection against port scanning ```bash 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 ```bash 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 ```bash iptables -N syn_flood iptables -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 DROP iptables -A INPUT -p icmp -m limit --limit 1/s --limit-burst 1 -j ACCEPT iptables -A INPUT -p icmp -m limit --limit 1/s --limit-burst 1 -j LOG --log-prefix PING-DROP: iptables -A INPUT -p icmp -j DROP iptables -A OUTPUT -p icmp -j ACCEPT ``` ##### Mitigating SYN Floods With SYNPROXY ```bash 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 ```bash iptables -A INPUT -p tcp ! --syn -m state --state NEW -j DROP ``` or ```bash iptables -t mangle -A PREROUTING -p tcp ! --syn -m conntrack --ctstate NEW -j DROP ``` #### Force Fragments packets check ```bash iptables -A INPUT -f -j DROP ``` #### XMAS packets ```bash iptables -A INPUT -p tcp --tcp-flags ALL ALL -j DROP ``` #### Drop all NULL packets ```bash iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP ``` #### Block Uncommon MSS Values ```bash iptables -t mangle -A PREROUTING -p tcp -m conntrack --ctstate NEW -m tcpmss ! --mss 536:65535 -j DROP ``` #### Block Packets With Bogus TCP Flags ```bash 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 (Spoofing) ```bash _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 ```