OPS535 Linux Firewall Review

• Text book: Chapter 13

Concepts

• Netfilter/iptables with iptables(legacy)
• Netfilter/nftables with iptables(nt_tables)
• firewall with firewalld (front end for netfilter/iptables and netfilter/nftables)

Command line tools

• iptables
• ip6tables
• arptables
• ebtables
• nft
• firewall-cmd

iptables

• raw table
  • PREROUTING chain
  • OUTPUT chain
• managle table
  • PREROUTING
  • INPUT
  • FORWARD
  • OUTPUT
  • POSTROUTING
• nat table
  • PREROUTING
  • INPUT
  • OUTPUT
  • POSTROUTING
• filter table
  • INPUT
  • FORWARD
  • OUTPUT
• security table
  • INPUT
  • FORWARD
  • OUTPUT

rules

iptables -t filter -A INPUT -p tcp --dport 22 -j ACCEPT
          |---------------| |---------------| |--------|
           where and when     match spec.       action