Basics

IPTables Basics

Default Tables

• filter
• nat
• mangle

filter Default Chains

• INPUT
• OUTPUT
• FORWARD

mangle Default Chains

• INPUT
• OUTPUT
• FORWARD
• PREROUTING
• POSTROUTING

nat Default Chains

• INPUT
• OUTPUT
• PREROUTING
• POSTROUTING

IPTables Chains Rules

• What exactly should happen to a packet
• Ordering is important
• Specify target using -j ACCEPT, DROP, REJECT, LOG
• Policy is default behavior like as drop everythings
• Default table is filter

IPTables Structure

#iptables -A {CHAIN} [ -i/-o interface ] [ -s/-d addr ] -p [ udp/tcp ] --sport/dport {port num} -j TARGET
---Example---
#iptables -A INPUT -i ens33 -s 192.168.1.0/24 -p tcp --dport 22 -j ACCEPT

Default Policy of Chain

#iptables -P [ ACCEPT | DROP | REJECT ] -t [ filter | nat | mangle ] [ CHAIN ]
---Example---
#iptables -P DROP -t filter INPUT